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    Gasoline Fuel-Injection
    System K-Jetronic
    Gasoline-engine management
    Technical Instruction
    Published by:
    © Robert Bosch GmbH, 2000
    Postfach 3002 20,
    D-70442 Stuttgart.
    Automotive Equipment Business Sector,
    Department for Automotive Services,
    Technical Publications (KH/PDI2).
    Dipl.-Ing. (FH) Horst Bauer.
    Editorial staff:
    Dipl.-Ing. Karl-Heinz Dietsche,
    Dipl.-Ing. (BA) Jürgen Crepin.
    Dipl.-Ing. (FH) Ulrich Adler,
    Joachim Kaiser,
    Berthold Gauder, Leinfelden-Echterdingen.
    Peter Girling.
    Technical graphics:
    Bauer & Partner, Stuttgart.
    Unless otherwise stated, the above are all
    employees of Robert Bosch GmbH, Stuttgart.
    Reproduction, copying, or translation of this
    publication, including excerpts therefrom, is only to
    ensue with our previous written consent and with
    source credit.
    Illustrations, descriptions, schematic diagrams,
    and other data only serve for explanatory purposes
    and for presentation of the text. They cannot be
    used as the basis for design, installation, or scope
    of delivery. We assume no liability for conformity of
    the contents with national or local legal regulations.
    We are exempt from liability.
    We reserve the right to make changes at any time.
    Printed in Germany.
    Imprimé en Allemagne.
    4th Edition, February 2000.
    English translation of the German edition dated:
    September 1998.
    Combustion in the gasoline engine
    The spark-ignition or
    Otto-cycle engine 2
    Gasoline-engine management
    Technical requirements 4
    Cylinder charge 5
    Mixture formation 7
    Gasoline-injection systems
    Overview 10
    System overview 13
    Fuel supply 14
    Fuel metering 18
    Adapting to operating conditions 24
    Supplementary functions 30
    Exhaust-gas treatment 32
    Electrical circuitry 36
    Workshop testing techniques 38
    Since its introduction, the K-Jetronic
    gasoline-injection system has proved
    itself in millions of vehicles.
    This development was a direct result
    of the advantages which are inherent
    in the injection of gasoline with
    regard to demands for economy of
    operation, high output power, and
    last but not least improvements to
    the quality of the exhaust gases
    emitted by the vehicle. Whereas the
    call for higher engine output was the
    foremost consideration at the start of
    the development work on gasoline
    injection, today the target is to
    achieve higher fuel economy and
    lower toxic emissions.
    Between the years 1973 and 1995,
    the highly reliable, mechanical multipoint
    injection system K-Jetronic
    was installed as Original Equipment
    in series-production vehicles. Today,
    it has been superseded by gasoline
    injection systems which thanks to
    electronics have been vastly improved
    and expanded in their functions.
    Since this point, the K-Jetronic
    has now become particularly important
    with regard to maintenance and
    This manual will describe the
    K-Jetronic’s function and its particular
    The spark-ignition
    or Otto-cycle engine
    Operating concept
    The spark-ignition or Otto-cycle1)
    powerplant is an internal-combustion (IC)
    engine that relies on an externallygenerated
    ignition spark to transform the
    chemical energy contained in fuel into
    kinetic energy.
    Today’s standard spark-ignition engines
    employ manifold injection for mixture
    formation outside the combustion
    chamber. The mixture formation system
    produces an air/fuel mixture (based on
    gasoline or a gaseous fuel), which is
    then drawn into the engine by the suction
    generated as the pistons descend. The
    future will see increasing application of
    systems that inject the fuel directly into the
    combustion chamber as an alternate
    concept. As the piston rises, it compresses
    the mixture in preparation for the timed
    ignition process, in which externallygenerated
    energy initiates combustion via
    the spark plug. The heat released in the
    combustion process pressurizes the
    cylinder, propelling the piston back down,
    exerting force against the crankshaft and
    performing work. After each combustion
    stroke the spent gases are expelled from
    the cylinder in preparation for ingestion of
    a fresh charge of air/fuel mixture. The
    primary design concept used to govern
    this gas transfer in powerplants for
    automotive applications is the four-stroke
    principle, with two crankshaft revolutions
    being required for each complete cycle.
    The four-stroke principle
    The four-stroke engine employs flowcontrol
    valves to govern gas transfer
    (charge control). These valves open and
    close the intake and exhaust tracts
    leading to and from the cylinder:
    1st stroke: Induction,
    2nd stroke: Compression and ignition,
    3rd stroke: Combustion and work,
    4th stroke: Exhaust.
    Induction stroke
    Intake valve: open,
    Exhaust valve: closed,
    Piston travel: downward,
    Combustion: none.
    The piston’s downward motion increases
    the cylinder’s effective volume to draw
    fresh air/fuel mixture through the passage
    exposed by the open intake valve.
    Compression stroke
    Intake valve: closed,
    Exhaust valve: closed,
    Piston travel: upward,
    Combustion: initial ignition phase.
    Combustion in
    the gasoline
    Combustion in
    the gasoline engine
    Reciprocating piston-engine design concept
    OT = TDC (Top Dead Center); UT = BDC (Bottom
    Dead Center), Vh Swept volume, VC Compressed
    volume, s Piston stroke.
    Fig. 1
    1) After Nikolaus August Otto (1832 –1891), who
    unveiled the first four-stroke gas-compression engine
    at the Paris World Exhibition in 1876.
    As the piston travels upward it reduces
    the cylinder’s effective volume to
    compress the air/fuel mixture. Just before
    the piston reaches top dead center (TDC)
    the spark plug ignites the concentrated
    air/fuel mixture to initiate combustion.
    Stroke volume Vh
    and compression volume VC
    provide the basis for calculating the
    compression ratio
    e = (Vh+VC)/VC.
    Compression ratios e range from 7...13,
    depending upon specific engine design.
    Raising an IC engine’s compression ratio
    increases its thermal efficiency, allowing
    more efficient use of the fuel. As an
    example, increasing the compression ratio
    from 6:1 to 8:1 enhances thermal
    efficiency by a factor of 12 %. The latitude
    for increasing compression ratio is
    restricted by knock. This term refers to
    uncontrolled mixture inflammation characterized
    by radical pressure peaks.
    Combustion knock leads to engine
    damage. Suitable fuels and favorable
    combustion-chamber configurations can
    be applied to shift the knock threshold into
    higher compression ranges.
    Power stroke
    Intake valve: closed,
    Exhaust valve: closed,
    Piston travel: upward,
    Combustion: combustion/post-combustion
    The ignition spark at the spark plug
    ignites the compressed air/fuel mixture,
    thus initiating combustion and the
    attendant temperature rise.
    This raises pressure levels within the
    cylinder to propel the piston downward.
    The piston, in turn, exerts force against
    the crankshaft to perform work; this
    process is the source of the engine’s
    Power rises as a function of engine speed
    and torque (P = M×w).
    A transmission incorporating various
    conversion ratios is required to adapt the
    combustion engine’s power and torque
    curves to the demands of automotive
    operation under real-world conditions.
    Exhaust stroke
    Intake valve: closed,
    Exhaust valve: open,
    Piston travel: upward,
    Combustion: none.
    As the piston travels upward it forces the
    spent gases (exhaust) out through the
    passage exposed by the open exhaust
    valve. The entire cycle then recommences
    with a new intake stroke. The intake and
    exhaust valves are open simultaneously
    during part of the cycle. This overlap
    exploits gas-flow and resonance patterns
    to promote cylinder charging and
    Otto cycle
    Operating cycle of the 4-stroke spark-ignition engine
    Fig. 2
    Stroke 1: Induction Stroke 2: Compression Stroke 3: Combustion Stroke 4: Exhaust
    Technical requirements
    Spark-ignition (SI)
    engine torque
    The power P furnished by the sparkignition
    engine is determined by the
    available net flywheel torque and the
    engine speed.
    The net flywheel torque consists of the
    force generated in the combustion
    process minus frictional losses (internal
    friction within the engine), the gasexchange
    losses and the torque required
    to drive the engine ancillaries (Figure 1).
    The combustion force is generated
    during the power stroke and is defined by
    the following factors:
    – The mass of the air available for
    combustion once the intake valves
    have closed,
    – The mass of the simultaneously
    available fuel, and
    – The point at which the ignition spark
    initiates combustion of the air/fuel
    Primary enginemanagement
    The engine-management system’s first
    and foremost task is to regulate the
    engine’s torque generation by controlling
    all of those functions and factors in the
    various engine-management subsystems
    that determine how much torque is
    Cylinder-charge control
    In Bosch engine-management systems
    featuring electronic throttle control (ETC),
    the “cylinder-charge control” subsystem
    determines the required induction-air
    mass and adjusts the throttle-valve
    opening accordingly. The driver exercises
    direct control over throttle-valve opening
    on conventional injection systems via the
    physical link with the accelerator pedal.
    Mixture formation
    The “mixture formation” subsystem calculates
    the instantaneous mass fuel
    requirement as the basis for determining
    the correct injection duration and optimal
    injection timing.
    Driveline torque factors
    1 Ancillary equipment
    a/c compressor, etc.),
    2 Engine,
    3 Clutch,
    4 Transmission.
    Fig. 1
    Air mass (fresh induction charge)
    Fuel mass
    Ignition angle (firing point)
    Gas-transfer and friction
    Clutch/converter losses and conversion ratios
    Transmission losses and conversion ratios
    output torque
    output torque
    – –
    – –
    Clutc–h Tran–smission
    1 1 2 3 4
    Finally, the “ignition” subsystem determines
    the crankshaft angle that
    corresponds to precisely the ideal instant
    for the spark to ignite the mixture.
    The purpose of this closed-loop control
    system is to provide the torque
    demanded by the driver while at the
    same time satisfying strict criteria in the
    areas of
    – Exhaust emissions,
    – Fuel consumption,
    – Power,
    – Comfort and convenience, and
    – Safety.
    Cylinder charge
    The gas mixture found in the cylinder
    once the intake valve closes is referred to
    as the cylinder charge, and consists of
    the inducted fresh air-fuel mixture along
    with residual gases.
    Fresh gas
    The fresh mixture drawn into the cylinder
    is a combination of fresh air and the fuel
    entrained with it. While most of the fresh
    air enters through the throttle valve,
    supplementary fresh gas can also be
    drawn in through the evaporativeemissions
    control system (Figure 2). The
    air entering through the throttle-valve and
    remaining in the cylinder after intakevalve
    closure is the decisive factor
    defining the amount of work transferred
    through the piston during combustion,
    and thus the prime determinant for the
    amount of torque generated by the
    engine. In consequence, modifications to
    enhance maximum engine power and
    torque almost always entail increasing
    the maximum possible cylinder charge.
    The theoretical maximum charge is
    defined by the volumetric capacity.
    Residual gases
    The portion of the charge consisting of
    residual gases is composed of
    – The exhaust-gas mass that is not
    discharged while the exhaust valve is
    open and thus remains in the cylinder,
    – The mass of recirculated exhaust gas
    (on systems with exhaust-gas recirculation,
    Figure 2).
    The proportion of residual gas is determined
    by the gas-exchange process.
    Although the residual gas does not
    participate directly in combustion, it does
    influence ignition patterns and the actual
    combustion sequence. The effects of this
    residual-gas component may be thoroughly
    desirable under part-throttle operation.
    Larger throttle-valve openings to compensate
    for reductions in fresh-gas filling
    Cylinder charge in the spark-ignition engine
    1 Air and fuel vapor,
    2 Purge valve
    with variable aperture,
    3 Link to evaporative-emissions
    control system,
    4 Exhaust gas,
    5 EGR valve with
    variable aperture,
    6 Mass airflow (barometric pressure pU),
    7 Mass airflow
    (intake-manifold pressure ps),
    8 Fresh air charge
    (combustion-chamber pressure pB),
    9 Residual gas charge
    (combustion-chamber pressure pB),
    10 Exhaust gas (back-pressure pA),
    11 Intake valve,
    12 Exhaust valve,
    a Throttle-valve angle.
    Fig. 2
    6 7 10
    2 3
    4 5
    11 12
    are needed to meet higher torque
    demand. These higher angles reduce the
    engine’s pumping losses, leading to
    lower fuel consumption. Precisely regulated
    injection of residual gases can
    also modify the combustion process to
    reduce emissions of nitrous oxides (NOx)
    and unburned hydrocarbons (HC).
    Control elements
    Throttle valve
    The power produced by the sparkignition
    engine is directly proportional to
    the mass airflow entering it. Control of
    engine output and the corresponding
    torque at each engine speed is regulated
    by governing the amount of air being
    inducted via the throttle valve. Leaving
    the throttle valve partially closed restricts
    the amount of air being drawn into the
    engine and reduces torque generation.
    The extent of this throttling effect
    depends on the throttle valve’s position
    and the size of the resulting aperture.
    The engine produces maximum power
    when the throttle valve is fully open
    (WOT, or wide open throttle).
    Figure 3 illustrates the conceptual
    correlation between fresh-air charge
    density and engine speed as a function
    of throttle-valve aperture.
    Gas exchange
    The intake and exhaust valves open and
    close at specific points to control the
    transfer of fresh and residual gases. The
    ramps on the camshaft lobes determine
    both the points and the rates at which the
    valves open and close (valve timing) to
    define the gas-exchange process, and
    with it the amount of fresh gas available
    for combustion.
    Valve overlap defines the phase in which
    the intake and exhaust valves are open
    simultaneously, and is the prime factor in
    determining the amount of residual gas
    remaining in the cylinder. This process is
    known as "internal" exhaust-gas
    recirculation. The mass of residual gas
    can also be increased using "external"
    exhaust-gas recirculation, which relies
    on a supplementary EGR valve linking
    the intake and exhaust manifolds. The
    engine ingests a mixture of fresh air and
    exhaust gas when this valve is open.
    Pressure charging
    Because maximum possible torque is
    proportional to fresh-air charge density, it
    is possible to raise power output by
    compressing the air before it enters the
    Dynamic pressure charging
    A supercharging (or boost) effect can be
    obtained by exploiting dynamics within
    the intake manifold. The actual degree of
    boost will depend upon the manifold’s
    configuration as well as the engine’s
    instantaneous operating point
    (essentially a function of the engine’s
    speed, but also affected by load factor).
    The option of varying intake-manifold
    geometry while the vehicle is actually
    being driven, makes it possible to employ
    dynamic precharging to increase the
    maximum available charge mass through
    a wide operational range.
    Mechanical supercharging
    Further increases in air mass are
    available through the agency of
    Throttle-valve map for spark-ignition engine
    Throttle valve at intermediate aperture
    Fig. 3Fresh gas charge
    min. max.
    Throttle valve
    completely open
    Throttle valve
    completely closed
    mechanically driven compressors powered
    by the engine’s crankshaft, with the
    two elements usually rotating at an invariable
    relative ratio. Clutches are often
    used to control compressor activation.
    Exhaust-gas turbochargers
    Here the energy employed to power the
    compressor is extracted from the exhaust
    gas. This process uses the energy that
    naturally-aspirated engines cannot
    exploit directly owing to the inherent
    restrictions imposed by the gas expansion
    characteristics resulting from the
    crankshaft concept. One disadvantage is
    the higher back-pressure in the exhaust
    gas exiting the engine. This backpressure
    stems from the force needed to
    maintain compressor output.
    The exhaust turbine converts the
    exhaust-gas energy into mechanical
    energy, making it possible to employ an
    impeller to precompress the incoming
    fresh air. The turbocharger is thus a
    combination of the turbine in the exhaustfas
    flow and the impeller that compresses
    the intake air.
    Figure 4 illustrates the differences in the
    torque curves of a naturally-aspirated
    engine and a turbocharged engine.
    Mixture formation
    Air-fuel mixture
    Operation of the spark-ignition engine is
    contingent upon availability of a mixture
    with a specific air/fuel (A/F) ratio. The
    theoretical ideal for complete combustion
    is a mass ratio of 14.7:1, referred to as
    the stoichiometric ratio. In concrete terms
    this translates into a mass relationship of
    14.7 kg of air to burn 1 kg of fuel, while
    the corresponding volumetric ratio is
    roughly 9,500 litres of air for complete
    combustion of 1 litre of fuel.
    The air-fuel mixture is a major factor in
    determining the spark-ignition engine’s
    rate of specific fuel consumption.
    Genuine complete combustion and
    absolutely minimal fuel consumption
    would be possible only with excess air,
    but here limits are imposed by such
    considerations as mixture flammability
    and the time available for combustion.
    The air-fuel mixture is also vital in
    determining the efficiency of exhaust-gas
    treatment system. The current state-ofthe-
    art features a 3-way catalytic
    converter, a device which relies on a
    stoichiometric A/F ratio to operate at
    maximum efficiency and reduce undesirable
    exhaust-gas components by
    more than 98%.
    Current engines therefore operate with a
    stoichiometric A/F ratio as soon as the
    engine’s operating status permits
    Certain engine operating conditions
    make mixture adjustments to nonstoichiometric
    ratios essential. With a
    cold engine for instance, where specific
    adjustments to the A/F ratio are required.
    As this implies, the mixture-formation
    system must be capable of responding to
    a range of variable requirements.
    Torque curves for turbocharged
    and atmospheric-induction engines
    with equal power outputs
    1 Engine with turbocharger,
    2 Atmospheric-induction engine.
    Fig. 4
    Engine torque Md Engine rpm nn
    Excess-air factor
    The designation l (lambda) has been
    selected to identify the excess-air factor
    (or air ratio) used to quantify the spread
    between the actual current mass A/F ratio
    and the theoretical optimum (14.7:1):
    l = Ratio of induction air mass to air
    requirement for stoichiometric combustion.
    l = 1: The inducted air mass corresponds
    to the theoretical requirement.
    l < 1: Indicates an air deficiency,
    producing a corresponding rich mixture.
    Maximum power is derived from l =
    l > 1: This range is characterized by
    excess air and lean mixture, leading to
    lower fuel consumption and reduced
    power. The potential maximum value for l
    – called the “lean-burn limit (LML)” – is
    essentially defined by the design of the
    engine and of its mixture formation/
    induction system. Beyond the
    lean-burn limit the mixture ceases to be
    ignitable and combustion miss sets in,
    accompanied by substantial degeneration
    of operating smoothness.
    In engines featuring systems to inject fuel
    directly into the chamber, these operate
    with substantially higher excess-air
    factors (extending to l = 4) since combustion
    proceeds according to different
    Spark-ignition engines with manifold
    injection produce maximum power at air
    deficiencies of 5...15 % (l = 0.95...0.85),
    but maximum fuel economy comes in at
    10...20% excess air (l = 1.1...1.2).
    Figures 1 and 2 illustrate the effect of the
    excess-air factor on power, specific fuel
    consumption and generation of toxic
    emissions. As can be seen, there is no
    single excess-air factor which can
    simultaneously generate the most
    favorable levels for all three factors. Air
    factors of l = 0.9...1.1 produce
    “conditionally optimal” fuel economy with
    “conditionally optimal” power generation
    in actual practice.
    Once the engine warms to its normal
    operating temperature, precise and
    consistent maintenance of l = 1 is vital
    for the 3-way catalytic treatment of
    exhaust gases. Satisfying this requirement
    entails exact monitoring of
    induction-air mass and precise metering
    of fuel mass.
    Optimal combustion from current engines
    equipped with manifold injection
    relies on formation of a homogenous
    mixture as well as precise metering of the
    injected fuel quantity. This makes
    effective atomization essential. Failure to
    satisfy this requirement will foster the
    formation of large droplets of condensed
    fuel on the walls of the intake tract and in
    the combustion chamber. These droplets
    will fail to combust completely and the
    ultimate result will be higher HC
    Effects of excess-air factor l on power P and
    specific fuel consumption be.
    a Rich mixture (air deficiency),
    b Lean mixture (excess air).
    Fig. 1
    Effect of excess-air factor l on untreated
    exhaust emissions
    Fig. 2
    0.8 1.0 1.2
    a b
    Power P,
    Specific fuel consumption be
    Excess-air factor l
    0.6 1.0 1.4
    Relative quantities of
    CO; HC; NOX
    Excess-air factor l
    0.8 1.2
    HC NOX
    Adapting to specific
    operating conditions
    Certain operating states cause fuel
    requirements to deviate substantially from
    the steady-state requirements of an engine
    warmed to its normal temperature, thus
    necessitating corrective adaptations in the
    mixture-formation apparatus. The following
    descriptions apply to the conditions
    found in engines with manifold injection.
    Cold starting
    During cold starts the relative quantity of
    fuel in the inducted mixture decreases: the
    mixture “goes lean.” This lean-mixture
    phenomenon stems from inadequate
    blending of air and fuel, low rates of fuel
    vaporization, and condensation on the
    walls of the inlet tract, all of which are
    promoted by low temperatures. To compensate
    for these negative factors, and to
    facilitate cold starting, supplementary fuel
    must be injected into the engine.
    Post-start phase
    Following low-temperature starts,
    supplementary fuel is required for a brief
    period, until the combustion chamber
    heats up and improves the internal
    mixture formation. This richer mixture
    also increases torque to furnish a
    smoother transition to the desired idle
    Warm-up phase
    The warm-up phase follows on the heels
    of the starting and immediate post-start
    phases. At this point the engine still
    requires an enriched mixture to offset the
    fuel condensation on the intake-manifold
    walls. Lower temperatures are synonymous
    with less efficient fuel processing
    (owing to factors such as poor mixing
    of air and fuel and reduced fuel vaporization).
    This promotes fuel precipitation
    within the intake manifold, with
    the formation of condensate fuel that will
    only vaporize later, once temperatures
    have increased. These factors make it
    necessary to provide progressive mixture
    enrichment in response to decreasing
    Idle and part-load
    Idle is defined as the operating status in
    which the torque generated by the engine
    is just sufficient to compensate for friction
    losses. The engine does not provide
    power to the flywheel at idle. Part-load (or
    part-throttle) operation refers to the
    range of running conditions between idle
    and generation of maximum possible
    torque. Today’s standard concepts rely
    exclusively on stoichiometric mixtures for
    the operation of engines running at idle
    and part-throttle once they have warmed
    to their normal operating temperatures.
    Full load (WOT)
    At WOT (wide-open throttle) supplementary
    enrichment may be required. As
    Figure 1 indicates, this enrichment
    furnishes maximum torque and/or power.
    Acceleration and deceleration
    The fuel’s vaporization potential is strongly
    affected by pressure levels inside the
    intake manifold. Sudden variations in
    manifold pressure of the kind encountered
    in response to rapid changes in throttlevalve
    aperture cause fluctuations in the
    fuel layer on the walls of the intake tract.
    Spirited acceleration leads to higher
    manifold pressures. The fuel responds
    with lower vaporization rates and the fuel
    layer within the manifold runners expands.
    A portion of the injected fuel is thus lost in
    wall condensation, and the engine goes
    lean for a brief period, until the fuel layer
    restabilizes. In an analogous, but inverted,
    response pattern, sudden deceleration
    leads to rich mixtures. A temperaturesensitive
    correction function (transition
    compensation) adapts the mixture to
    maintain optimal operational response
    and ensure that the engine receives the
    consistent air/fuel mixture needed for
    efficient catalytic-converter performance.
    Trailing throttle (overrun)
    Fuel metering is interrupted during trailing
    throttle. Although this expedient saves
    fuel on downhill stretches, its primary
    purpose is to guard the catalytic converter
    against overheating stemming from poor
    and incomplete combustion (misfiring).
    Carburetors and gasoline-injection systems
    are designed for a single purpose:
    To supply the engine with the optimal airfuel
    mixture for any given operating
    conditions. Gasoline injection systems,
    and electronic systems in particular, are
    better at maintaining air-fuel mixtures
    within precisely defined limits, which
    translates into superior performance in
    the areas of fuel economy, comfort and
    convenience, and power. Increasingly
    stringent mandates governing exhaust
    emissions have led to a total eclipse of the
    carburetor in favor of fuel injection.
    Although current systems rely almost
    exclusively on mixture formation outside
    the combustion chamber, concepts based
    on internal mixture formation – with fuel
    being injected directly into the combustion
    chamber – were actually the foundation
    for the first gasoline-injection systems. As
    these systems are superb instruments for
    achieving further reductions in fuel
    consumption, they are now becoming an
    increasingly significant factor.
    Systems with
    external mixture formation
    The salient characteristic of this type of
    system is the fact that it forms the air-fuel
    mixture outside the combustion chamber,
    inside the intake manifold.
    Multipoint fuel injection
    Multipoint fuel injection forms the ideal
    basis for complying with the mixtureformation
    criteria described above. In this
    type of system each cylinder has its own
    injector discharging fuel into the area
    directly in front of the intake valve.
    Representative examples are the various
    versions of the KE and L-Jetronic systems
    (Figure 1).
    Mechanical injection systems
    The K-Jetronic system operates by
    injecting continually, without an external
    drive being necessary. Instead of
    being determined by the injection valve,
    fuel mass is regulated by the fuel
    Combined mechanical-electronic
    fuel injection
    Although the K-Jetronic layout served as
    the mechanical basis for the KE-Jetronic
    system, the latter employs expanded
    data-monitoring functions for more
    precise adaptation of injected fuel
    quantity to specific engine operating
    Electronic injection systems
    Injection systems featuring electronic
    control rely on solenoid-operated injection
    Multipoint fuel injection (MPI)
    1 Fuel,
    2 Air,
    3 Throttle valve,
    4 Intake manifold,
    5 Injectors,
    6 Engine.
    Gasoline-injection systems
    Fig. 1
    valves for intermittent fuel discharge. The
    actual injected fuel quantity is regulated
    by controlling the injector's opening time
    (with the pressure-loss gradient through
    the valve being taken into account in
    calculations as a known quantity).
    Examples: L-Jetronic, LH-Jetronic, and
    Motronic as an integrated engine-management
    Single-point fuel injection
    Single-point (throttle-body injection (TBI))
    fuel injection is the concept behind this
    electronically-controlled injection system
    in which a centrally located solenoidoperated
    injection valve mounted
    upstream from the throttle valve sprays
    fuel intermittently into the manifold. Mono-
    Jetronic and Mono-Motronic are the
    Bosch systems in this category (Figure 2).
    Systems for internal
    mixture formation
    Direct-injection (DI) systems rely on
    solenoid-operated injection valves to spray
    fuel directly into the combustion chamber;
    the actual mixture-formation process takes
    place within the cylinders, each of which
    has its own injector (Figure 3). Perfect
    atomization of the fuel emerging from the
    injectors is vital for efficient combustion.
    Under normal operating conditions, DI
    engines draw in only air instead of the
    combination of air and fuel common to
    conventional injection systems. This is one
    of the new system's prime advantages: It
    banishes all potential for fuel condensation
    within the runners of the intake manifold.
    External mixture formation usually
    provides a homogenous, stoichiometric airfuel
    mixture throughout the entire
    combustion chamber. In contrast, shifting
    the mixture-preparation process into the
    combustion chamber provides for two
    distinctive operating modes:
    With stratified-charge operation, only the
    mixture directly adjacent to the spark plug
    needs to be ignitable. The remainder of the
    air-fuel charge in the combustion chamber
    can consist solely of fresh and residual
    gases, without unburned fuel. This strategy
    furnishes an extremely lean overall mixture
    for idling and part-throttle operation, with
    commensurate reductions in fuel
    Homogenous operation reflects the
    conditions encountered in external mixture
    formation by employing uniform
    consistency for the entire air-fuel charge
    throughout the combustion chamber.
    Under these conditions all of the fresh air
    within the chamber participates in the
    combustion process. This operational
    mode is employed for WOT operation.
    MED-Motronic is used for closed-loop
    control of DI gasoline engines.
    Throttle-body fuel injection (TBI)
    1 Fuel,
    2 Air,
    3 Throttle valve,
    4 Intake manifold,
    5 Injector,
    6 Engine.
    Fig. 2
    Direct fuel injection (DI)
    1 Fuel,
    2 Air,
    3 Throttle valve
    4 Intake manifold,
    5 Injectors,
    6 Engine.
    Fig. 3
    The story of
    fuel injection
    The story of fuel injection
    The story of fuel injection extends
    back to cover a period of almost one
    hundred years.
    The Gasmotorenfabik Deutz was
    manufacturing plunger pumps for injecting
    fuel in a limited production
    series as early as 1898.
    A short time later the uses of the venturi-
    effect for carburetor design were
    discovered, and fuel-injection systems
    based on the technology of the time
    ceased to be competitive.
    Bosch started research on gasolineinjection
    pumps in 1912. The first
    aircraft engine featuring Bosch fuel injection,
    a 1,200-hp unit, entered series
    production in 1937; problems with carburetor
    icing and fire hazards had lent
    special impetus to fuel-injection development
    work for the aeronautics field.
    This development marks the beginning
    of the era of fuel injection at
    Bosch, but there was still a long path
    to travel on the way to fuel injection for
    passenger cars.
    1951 saw a Bosch direct-injection unit
    being featured as standard equipment
    on a small car for the first time. Several
    years later a unit was installed in
    the 300 SL, the legendary production
    sports car from Daimler-Benz.
    In the years that followed, development
    on mechanical injection pumps
    continued, and ...
    In 1967 fuel injection took another
    giant step forward: The first electronic
    injection system: the intake-pressurecontrolled
    In 1973 the air-flow-controlled L-Jetronic
    appeared on the market, at the
    same time as the K-Jetronic, which featured
    mechanical-hydraulic control and
    was also an air-flow-controlled system.
    In 1976, the K-Jetronic was the first
    automotive system to incorporate a
    Lambda closed-loop control.
    1979 marked the introduction of a new
    system: Motronic, featuring digital processing
    for numerous engine functions.
    This system combined L-Jetronic
    with electronic program-map control
    for the ignition. The first automotive
    In 1982, the K-Jetronic model became
    available in an expanded configuration,
    the KE-Jetronic, including an
    electronic closed-loop control circuit
    and a Lambda oxygen sensor.
    These were joined by Bosch Mono-
    Jetronic in 1987: This particularly costefficient
    single-point injection unit
    made it feasible to equip small vehicles
    with Jetronic, and once and for all made
    the carburetor absolutely superfluous.
    By the end of 1997, around 64 million
    Bosch engine-management systems
    had been installed in countless types of
    vehicles since the introduction of the
    D-Jetronic in 1967. In 1997 alone, the
    figure was 4.2 million, comprised of
    1 million throttle-body injection (TBI)
    systems and 3.2 million multipoint fuelinjection
    (MPI) systems.
    Bosch gasoline fuel injection
    from the year 1954
    System overview
    The K-Jetronic is a mechanically and
    hydraulically controlled fuel-injection system
    which needs no form of drive and
    which meters the fuel as a function of the
    intake air quantity and injects it continuously
    onto the engine intake valves.
    Specific operating conditions of the
    engine require corrective intervention in
    mixture formation and this is carried out
    by the K-Jetronic in order to optimize
    starting and driving performance, power
    output and exhaust composition. Owing
    to the direct air-flow sensing, the K-Jetronic
    system also allows for engine
    variations and permits the use of facilities
    for exhaust-gas aftertreatment for which
    precise metering of the intake air quantity
    is a prerequisite.
    The K-Jetronic was originally designed
    as a purely mechanical injection system.
    Today, using auxiliary electronic equipment,
    the system also permits the use of
    lambda closed-loop control.
    The K-Jetronic fuel-injection system
    covers the following functional areas:
    – Fuel supply,
    – Air-flow measurement and
    – Fuel metering.
    Fuel supply
    An electrically driven fuel pump delivers
    the fuel to the fuel distributor via a fuel
    accumulator and a filter. The fuel distributor
    allocates this fuel to the injection
    valves of the individual cylinders.
    Air-flow measurement
    The amount of air drawn in by the engine
    is controlled by a throttle valve and
    measured by an air-flow sensor.
    Fuel metering
    The amount of air, corresponding to the
    position of the throttle plate, drawn in by
    the engine serves as the criterion for
    metering of the fuel to the individual
    cylinders. The amount of air drawn in by
    the engine is measured by the air-flow
    sensor which, in turn, controls the fuel
    distributor. The air-flow sensor and the
    fuel distributor are assemblies which
    form part of the mixture control unit.
    Injection occurs continuously, i.e. without
    regard to the position of the intake valve.
    During the intake-valve closed phase, the
    fuel is “stored”. Mixture enrichment is
    controlled in order to adapt to various
    operating conditions such as start, warmup,
    idle and full load. In addition, supplementary
    functions such as overrun fuel
    cutoff, engine-speed limiting and closedloop
    lambda control are possible.
    Functional schematic of the K-Jetronic
    Fig. 1
    fuel pump
    Fuel filter
    Air filter
    Throttle valve
    Intake ports
    Injection valves
    control unit
    Fuel supply
    The fuel supply system comprises
    – Electric fuel pump,
    – Fuel accumulator,
    – Fine filter,
    – Primary-pressure regulator and
    – Injection valves.
    An electrically driven roller-cell pump
    pumps the fuel from the fuel tank at a
    pressure of over 5 bar to a fuel accumulator
    and through a filter to the fuel
    distributor. From the fuel distributor the
    fuel flows to the injection valves. The
    injection valves inject the fuel continuously
    into the intake ports of the
    engine. Thus the system designation K
    (taken from the German for continuous).
    When the intake valves open, the mixture
    is drawn into the cylinder.
    The fuel primary-pressure regulator
    maintains the supply pressure in the
    system constant and reroutes the excess
    fuel back to the fuel tank.
    Owing to continual scavenging of the fuel
    supply system, there is always cool fuel
    available. This avoids the formation of
    fuel-vapor bubbles and achieves good
    hot starting behavior.
    Electric fuel pump
    The electric fuel pump is a roller-cell
    pump driven by a permanent-magnet
    electric motor.
    The rotor plate which is eccentrically
    mounted in the pump housing is fitted
    with metal rollers in notches around its
    circumference which are pressed against
    the pump housing by centrifugal force
    and act as rolling seals. The fuel is carried
    in the cavities which form between
    the rollers. The pumping action takes
    place when the rollers, after having
    closed the inlet bore, force the trapped
    fuel in front of them until it can escape
    from the pump through the outlet bore
    (Figure 4). The fuel flows directly around
    the electric motor. There is no danger of
    explosion, however, because there is
    never an ignitable mixture in the pump
    Fig. 2
    Schematic diagram of the K-Jetronic system with closed-loop lambda control
    1 Fuel tank, 2 Electric fuel pump, 3 Fuel accumulator, 4 Fuel filter, 5 Warm-up regulator, 6 Injection valve,
    7 Intake manifold, 8 Cold-start valve, 9 Fuel distributor, 10 Air-flow sensor, 11 Timing valve, 12 Lambda
    sensor, 13 Thermo-time switch, 14 Ignition distributor, 15 Auxiliary-air device, 16 Throttle-valve switch,
    17 ECU, 18 Ignition and starting switch, 19 Battery.
    6 8
    The electric fuel pump delivers more fuel
    than the maximum requirement of the
    engine so that compression in the fuel
    system can be maintained under all operating
    conditions. A check valve in the
    pump decouples the fuel system from
    the fuel tank by preventing reverse flow of
    fuel to the fuel tank.
    The electric fuel pump starts to operate
    immediately when the ignition and starting
    switches are operated and remains
    switched on continuously after the engine
    has started. A safety circuit is incorporated
    to stop the pump running and, thus,
    to prevent fuel being delivered if the ignition
    is switched on but the engine has
    stopped turning (for instance in the case
    of an accident).
    The fuel pump is located in the immediate
    vicinity of the fuel tank and requires
    no maintenance.
    Fuel accumulator
    The fuel accumulator maintains the
    pressure in the fuel system for a certain
    time after the engine has been switched
    off in order to facilitate restarting, particularly
    when the engine is hot. The special
    design of the accumulator housing
    (Figure 5) deadens the sound of the fuel
    pump when the engine is running.
    The interior of the fuel accumulator is
    divided into two chambers by means of a
    diaphragm. One chamber serves as the
    accumulator for the fuel whilst the other
    represents the compensation volume
    and is connected to the atmosphere or to
    the fuel tank by means of a vent fitting.
    During operation, the accumulator
    chamber is filled with fuel and the diaphragm
    is caused to bend back against
    the force of the spring until it is halted by
    the stops in the spring chamber. The
    diaphragm remains in this position, which
    corresponds to the maximum accumulator
    volume, as long as the engine is
    Fuel accumulator
    a Empty, b Full.
    1 Spring chamber, 2 Spring, 3 Stop, 4 Diaphragm,
    5 Accumulator volume, 6 Fuel inlet or outlet,
    7 Connection to the atmosphere.
    Operation of roller-cell pump
    1 Suction side, 2 Rotor plate, 3 Roller,
    4 Roller race plate, 5 Pressure side.
    Electric fuel pump
    1 Suction side, 2 Pressure limiter, 3 Roller-cell
    pump, 4 Motor armature, 5 Check valve,
    6 Pressure side.
    3 4 5
    1 6
    1 5
    2 3 4
    1 2 3 4 5
    7 6
    Fig. 3
    Fig. 4
    Fig. 5
    UMK1653Y UMK0120-2Y UMK0121-2Y
    Fuel filter
    The fuel filter retains particles of dirt
    which are present in the fuel and which
    would otherwise have an adverse effect
    on the functioning of the injection system.
    The fuel filter contains a paper element
    with a mean pore size of 10 μm backed
    up by a fluff trap. This combination
    ensures a high degree of cleaning.
    The filter is held in place in the housing
    by means of a support plate. It is fitted in
    the fuel line downstream from the fuel
    accumulator and its service life depends
    upon the amount of dirt in the fuel. It is
    imperative that the arrow on the filter
    housing showing the direction of fuel flow
    through the filter is observed when the
    filter is replaced.
    Primary-pressure regulator
    The primary-pressure regulator maintains
    the pressure in the fuel system
    It is incorporated in the fuel distributor
    and holds the delivery pressure (system
    pressure) at about 5 bar. The fuel pump
    always delivers more fuel than is required
    by the vehicle engine, and this causes a
    plunger to shift in the pressure regulator
    and open a port through which excess
    fuel can return to the tank.
    The pressure in the fuel system and the
    force exerted by the spring on the
    pressure-regulator plunger balance each
    other out. If, for instance, fuel-pump
    delivery drops slightly, the plunger is
    shifted by the spring to a corresponding
    new position and in doing so closes off
    the port slightly through which the excess
    fuel returns to the tank. This means that
    less fuel is diverted off at this point and
    the system pressure is controlled to its
    specified level.
    When the engine is switched off, the fuel
    pump also switches off and the primary
    pressure drops below the opening pressure
    of the injection valves. The pressure
    regulator then closes the return-flow port
    and thus prevents the pressure in the fuel
    system from sinking any further (Fig. 8).
    Fuel-injection valves
    The injection valves open at a given pressure
    and atomize the fuel through oscillation
    of the valve needle. The injection
    valves inject the fuel metered to them into
    the intake passages and onto the intake
    valves. They are secured in special
    Primary-pressure regulator fitted to fuel distributor
    a In rest position, b In actuated position.
    1 System-pressure entry, 2 Seal, 3 Return to fuel tank, 4 Plunger, 5 Spring.
    a b
    2 3 4 5
    1 2 3
    Fig. 7
    Fuel filter
    1 Paper element,
    2 Strainer,
    3 Support
    Fig. 6
    holders to insulate them against the heat
    radiated from the engine. The injection
    valves have no metering function themselves,
    and open of their own accord
    when the opening pressure of e.g. 3.5
    bar is exceeded. They are fitted with a
    valve needle (Fig. 9) which oscillates
    (“chatters”) audibly at high frequency
    when fuel is injected. This results in excellent
    atomization of the fuel even with
    the smallest of injection quantities. When
    the engine is switched off, the injection
    valves close tightly when the pressure in
    the fuel-supply system drops below their
    opening pressure. This means that no
    more fuel can enter the intake passages
    once the engine has stopped.
    Air-shrouded fuel-injection valves
    Air-shrouded injection valves improve the
    mixture formation particularly at idle.
    Using the pressure drop across the
    throttle valve, a portion of the air inducted
    by the engine is drawn into the cylinder
    through the injection valve (Fig. 20): The
    result is excellent atomization of the fuel
    at the point of exit (Fig. 10). Air-shrouded
    injection valves reduce fuel consumption
    and toxic emission constituents.
    Pressure curve after engine switchoff
    Firstly pressure falls from the normal system
    pressure (1) to the pressure-regulator closing
    pressure (2). The fuel accumulator then causes
    it to increase to the level (3) which is below the
    opening pressure (4) of the injection valves.
    Fuel-injection valve
    a In rest position,
    b In actuated position.
    1 Valve housing,
    2 Filter,
    3 Valve needle,
    4 Valve seat.
    Pressure p
    Time t
    3 4
    a b
    Fig. 8
    Fig. 9
    UMK0069-2Y UMK0018E
    Fig. 10
    Spray pattern of an injection valve without
    air-shrouding (left) and with air-shrouding (right).
    Fuel metering
    The task of the fuel-management system
    is to meter a quantity of fuel corresponding
    to the intake air quantity.
    Basically, fuel metering is carried out
    by the mixture control unit. This comprises
    the air-flow sensor and the fuel
    In a number of operating modes however,
    the amount of fuel required deviates
    greatly from the “standard” quantity and it
    becomes necessary to intervene in the
    mixture formation system (see section
    “Adaptation to operating conditions”).
    Air-flow sensor
    The quantity of air drawn in by the engine
    is a precise measure of its operating
    load. The air-flow sensor operates according
    to the suspended-body principle,
    and measures the amount of air drawn in
    by the engine.
    The intake air quantity serves as the
    main actuating variable for determining
    the basic injection quantity. It is the
    appropriate physical quantity for deriving
    the fuel requirement, and changes in the
    induction characteristics of the engine
    have no effect upon the formation of the
    air-fuel mixture. Since the air drawn in by
    the engine must pass through the air-flow
    sensor before it reaches the engine, this
    means that it has been measured and
    the control signal generated before it
    actually enters the engine cylinders. The
    result is that, in addition to other
    measures described below, the correct
    mixture adaptation takes place at all
    air-flow sensor
    a Sensor plate in its
    zero position,
    b Sensor plate in its
    operating position.
    1 Air funnel,
    2 Sensor plate,
    3 Relief cross-section,
    4 Idle-mixture
    adjusting screw,
    5 Pivot,
    6 Lever,
    7 Leaf spring.
    Principle of the air-flow sensor
    a Small amount of air drawn in: sensor plate only
    lifted slightly, b Large amount of air drawn in:
    sensor plate is lifted considerably further.
    1 2 3 4 5
    7 6
    Fig. 11
    Fig. 12
    UMK1654Y UMK0072Y
    The air-flow sensor is located upstream
    of the throttle valve so that it measures all
    the air which enters the engine cylinders.
    It comprises an air funnel in which the
    sensor plate (suspended body) is free to
    pivot. The air flowing through the funnel
    deflects the sensor plate by a given
    amount out of its zero position, and this
    movement is transmitted by a lever system
    to a control plunger which determines
    the basic injection quantity required
    for the basic functions. Considerable
    pressure shocks can occur in the
    intake system if backfiring takes place in
    the intake manifold. For this reason, the
    air-flow sensor is so designed that the
    sensor plate can swing back in the
    opposite direction in the event of misfire,
    and past its zero position to open a relief
    cross-section in the funnel. A rubber
    buffer limits the downward stroke (the
    upwards stroke on the downdraft air-flow
    sensor). A counterweight compensates
    for the weight of the sensor plate and
    lever system (this is carried out by an
    extension spring on the downdraft airflow
    sensor). A leaf spring ensures the
    correct zero position in the switched-off
    Fuel distributor
    Depending upon the position of the plate
    in the air-flow sensor, the fuel distributor
    meters the basic injection quantity to the
    individual engine cylinders. The position
    of the sensor plate is a measure of the
    amount of air drawn in by the engine. The
    position of the plate is transmitted to the
    control plunger by a lever.
    Barrel with metering slits and control plunger
    a Zero (inoperated position), b Part load, c Full load.
    1 Control pressure, 2 Control plunger, 3 Metering slit in the barrel, 4 Control edge, 5 Fuel inlet,
    6 Barrel with metering slits.
    Barrel with metering slits
    1 Intake air, 2 Control pressure, 3 Fuel inlet,
    4 Metered quantity of fuel, 5 Control plunger,
    6 Barrel with metering slits, 7 Fuel distributor.


    a 1 b c

    Fig. 13
    Fig. 14
    UMK1497Y UMK1496Y
    Depending upon its position in the barrel
    with metering slits, the control plunger
    opens or closes the slits to a greater or
    lesser extent. The fuel flows through the
    open section of the slits to the differential
    pressure valves and then to the fuel
    injection valves. If sensor-plate travel is
    only small, then the control plunger is
    lifted only slightly and, as a result, only a
    small section of the slit is opened for the
    passage of fuel. With larger plunger
    travel, the plunger opens a larger section
    of the slits and more fuel can flow. There
    is a linear relationship between sensorplate
    travel and the slit section in the
    barrel which is opened for fuel flow.
    A hydraulic force generated by the socalled
    control pressure is applied to the
    control plunger. It opposes the movement
    resulting from sensor-plate deflection.
    One of its functions is to ensure that the
    control plunger follows the sensor-plate
    movement immediately and does not, for
    instance, stick in the upper end position
    when the sensor plate moves down again.
    Further functions of the control pressure
    are discussed in the sections “Warm-up
    enrichment” and “Full-load enrichment”.
    Control pressure
    The control pressure is tapped from the
    primary pressure through a restriction
    bore (Figure 16). This restriction bore
    serves to decouple the control-pressure
    circuit and the primary-pressure circuit
    from one another. A connection line joins
    the fuel distributor and the warm-up
    regulator (control-pressure regulator).
    When starting the cold engine, the
    control pressure is about 0.5 bar. As the
    engine warms up, the warm-up regulator
    increases the control pressure to about
    3.7 bar (Figure 26).
    The control pressure acts through a
    damping restriction on the control
    plunger and thereby develops the force
    which opposes the force of the air in the
    air-flow sensor. In doing so, the restriction
    dampens a possible oscillation of the
    sensor plate which could result due to
    pulsating air-intake flow.
    The control pressure influences the fuel
    distribution. If the control pressure is low,
    the air drawn in by the engine can deflect
    the sensor plate further. This results in
    the control plunger opening the metering
    slits further and the engine being allocated
    more fuel. On the other hand, if the
    control pressure is high, the air drawn in
    by the engine cannot deflect the sensor
    plate so far and, as a result, the engine
    receives less fuel. In order to fully seal off
    the control-pressure circuit with absolute
    certainty when the engine has been
    switched off, and at the same time to
    maintain the pressure in the fuel circuit,
    the return line of the warm-up regulator is
    fitted with a check valve. This (push-up)
    valve is attached to the primary-pressure
    regulator and is held open during operation
    by the pressure-regulator plunger.
    When the engine is switched off and the
    plunger of the primary-pressure regulator
    returns to its zero position, the check
    valve is closed by a spring (Figure 17).
    Differential-pressure valves
    The differential-pressure valves in the
    fuel distributor result in a specific pressure
    drop at the metering slits.
    The air-flow sensor has a linear characteristic.
    This means that if double the
    quantity of air is drawn in, the sensor-
    Barrel with metering slits
    The slits are shown enlarged (the actual slit is
    about 0.2 mm wide).
    Fig. 15
    plate travel is also doubled. If this travel is
    to result in a change of delivered fuel in
    the same relationship, in this case double
    the travel equals double the quantity,
    then a constant drop in pressure must
    be guaranteed at the metering slits
    (Figure 14), regardless of the amount of
    fuel flowing through them.
    The differential-pressure valves maintain
    the differential pressure between the
    upper and lower chamber constant regardless
    of fuel throughflow. The differential
    pressure is 0.1 bar.
    The differential-pressure valves achieve
    a high metering accuracy and are of the
    flat-seat type. They are fitted in the fuel
    Primary pressure
    and control pressure
    1 Control-pressure
    effect (hydraulic
    2 Damping restriction,
    3 Line to warm-up regulator,
    4 Decoupling restriction
    5 Primary pressure
    (delivery pressure),
    6 Effect of air pressure.
    regulator with pushup
    valve in the
    a In zero (inoperated)
    b In operating position.
    1 Primary pressure
    2 Return (to fuel tank),
    3 Plunger of the
    4 Push-up valve,
    5 Control-pressure
    intake (from warmup

    6 5

    2 3 4
    Fig. 17
    Fig. 16
    UMK1499Y UMK1498Y
    distributor and one such valve is allocated
    to each metering slit. A diaphragm
    separates the upper and lower chambers
    of the valve (Figures 18 and 19). The
    lower chambers of all the valves are connected
    with one another by a ring main
    and are subjected to the primary pressure
    (delivery pressure). The valve seat
    is located in the upper chamber. Each
    upper chamber is connected to a
    metering slit and its corresponding connection
    to the fuel-injection line. The
    upper chambers are completely sealed
    off from each other. The diaphragms are
    spring-loaded and it is this helical spring
    that produces the pressure differential.
    Differential-pressure valve
    a Diaphragm
    position with a
    low injected
    fuel quantity
    b Diaphragm
    position with a
    large injected
    fuel quantity

    Fig. 18
    If a large basic fuel quantity flows into the
    upper chamber through the metering slit,
    the diaphragm is bent downwards and
    enlarges the valve cross-section at the
    outlet leading to the injection valve until
    the set differential pressure once again
    If the fuel quantity drops, the valve crosssection
    is reduced owing to the equilibrium
    of forces at the diaphragm until the
    differential pressure of 0.1 bar is again
    This causes an equilibrium of forces to
    prevail at the diaphragm which can be
    maintained for every basic fuel quantity
    by controlling the valve cross-section.
    Mixture formation
    The formation of the air-fuel mixture
    takes place in the intake ports and
    cylinders of the engine.
    The continually injected fuel coming from
    the injection valves is “stored” in front of
    the intake valves. When the intake valve
    is opened, the air drawn in by the engine
    carries the waiting “cloud” of fuel with it
    into the cylinder. An ignitable air-fuel
    mixture is formed during the induction
    stroke due to the swirl effect.
    Air-shrouded fuel-injection valves favor
    mixture formation since they atomize
    the fuel very well at the outlet point
    (Figures 10, 20).
    Fuel distributor with differential-pressure valves
    1 Fuel intake
    2 Upper chamber of
    the differentialpressure
    3 Line to the fuelinjection
    4 Control plunger,
    5 Control edge and
    metering slit,
    6 Valve spring,
    7 Valve diaphragm,
    8 Lower chamber of
    the differentialpressure
    Mixture formation with air-shrouded fuelinjection
    1 Fuel-injection valve, 2 Air-supply line,
    3 Intake manifold, 4 Throttle valve.

    2 3 4 5 6
    8 7
    1 2 3 4


    Fig. 19
    Fig. 20
    UMK0068Y UMK1602Y
    Adaptation to operating
    In addition to the basic functions described
    up to now, the mixture has to be
    adapted during particular operating
    conditions. These adaptations (corrections)
    are necessary in order to optimize
    the power delivered, to improve the
    exhaust-gas composition and to improve
    the starting behavior and driveability.
    Basic mixture adaptation
    The basic adaptation of the air-fuel mixture
    to the operating modes of idle, part
    load and full load is by appropriately
    shaping the air funnel in the air-flow
    sensor (Figures 21 and 22).
    If the funnel had a purely conical shape,
    the result would be a mixture with a constant
    air-fuel ratio throughout the whole
    of the sensor plate range of travel (metering
    range). However, it is necessary to
    meter to the engine an air-fuel mixture
    which is optimal for particular operating
    modes such as idle, part load and full
    load. In practice, this means a richer
    mixture at idle and full load, and a leaner
    mixture in the part-load range. This
    adaptation is achieved by designing the
    air funnel so that it becomes wider in
    If the cone shape of the funnel is flatter
    than the basic cone shape (which was
    specified for a particular mixture, e.g. for
    ì = 1), this results in a leaner mixture. If
    the funnel walls are steeper than in the
    basic model, the sensor plate is lifted
    further for the same air throughput, more
    fuel is therefore metered by the control
    plunger and the mixture is richer. Consequently,
    this means that the air funnel can
    be shaped so that it is poss-ible to meter
    mixtures to the engine which have different
    air-fuel ratios depending upon the
    sensor-plate position in the funnel (which
    in turn corresponds to the particular
    engine operating mode i.e. idle, part load
    and full load). This results in a richer
    mixture for idle and full load (idle and fullload
    enrichment) and, by contrast, a
    leaner mixture for part load.
    Cold-start enrichment
    Depending upon the engine temperature,
    the cold-start valve injects extra fuel into
    the intake manifold for a limited period
    during the starting process.
    In order to compensate for the condensation
    losses due to condensation on the
    cold cylinder walls, and in order to facilitate
    starting the cold engine during cold
    starting, extra fuel must be injected at the
    instant of start-up. This extra fuel is injected
    by the cold-start valve into the
    intake manifold. The injection period of
    the cold-start valve is limited by a
    thermo-time switch depending upon the
    engine temperature.
    This process is known as cold-start enrichment
    and results in a “richer” air-fuel
    Influence of funnel-wall angle upon
    the sensor-plate deflection for identical air
    a The basic funnel
    shape results
    in stroke “h”,
    b Steep funnel
    walls result in
    stroke “h” for
    identical air
    c Flatter funnel
    shape results
    in reduced
    deflection “h”
    for identical air
    A Annular area
    opened by the
    sensor plate
    (identical in
    a, b and c).
    Adaptation of the air-funnel shape
    1 For maximum power, 2 For part load,
    3 For idle.
    Fig. 21
    Fig. 22
    UMK0155Y UMK0071Y
    mixture, i.e. the excess-air factor ì is
    temporarily less than 1.
    Cold-start valve
    The cold-start valve (Figure 23) is a
    solenoid-operated valve. An electromagnetic
    winding is fitted inside the
    valve. When unoperated, the movable
    electromagnet armature is forced against
    a seal by means of a spring and thus
    closes the valve. When the electromagnet
    is energized, the armature which
    consequently has lifted from the valve
    seat opens the passage for the flow of
    fuel through the valve. From here, the fuel
    enters a special nozzle at a tangent and
    is caused to rotate or swirl.
    The result is that the fuel is atomized very
    finely and enriches the mixture in the
    manifold downstream of the throttle
    valve. The cold-start valve is so positioned
    in the intake manifold that good
    distribution of the mixture to all cylinders
    is ensured.
    Thermo-time switch
    The thermo-time switch limits the duration
    of cold-start valve operation, depending
    upon temperature.
    The thermo-time switch (Figure 24)
    consists of an electrically heated bimetal
    strip which, depending upon its temperature
    opens or closes a contact. It is
    brought into operation by the ignition/
    starter switch, and is mounted at a
    position which is representative of engine
    temperature. During a cold start, it limits
    the “on” period of the cold-start valve. In
    case of repeated start attempts, or when
    starting takes too long, the cold-start
    valve ceases to inject.
    Its “on” period is determined by the
    thermo-time switch which is heated by
    engine heat as well as by its own built-in
    heater. Both these heating effects are
    necessary in order to ensure that the
    “on” period of the cold-start valve is
    limited under all conditions, and engine
    flooding prevented. During an actual cold
    start, the heat generated by the built-in
    heater is mainly responsible for the
    “on” period (switch off, for instance,
    at –20 °C after 7.5 seconds). With a
    warm engine, the thermo-time switch has
    already been heated up so far by engine
    heat that it remains open and prevents
    the cold-start valve from going into
    Cold-start valve in operated state
    1 Electrical connection, 2 Fuel supply with
    strainer, 3 Valve (electromagnet armature),
    4 Solenoid winding, 5 Swirl nozzle, 6 Valve seat.
    Thermo-time switch
    1 Electrical connection, 2 Housing, 3 Bimetal,
    4 Heating filament, 5 Electrical contact.
    Fig. 23 Fig. 24
    Warm-up enrichment
    Warm-up enrichment is controlled by
    the warm-up regulator. When the engine
    is cold, the warm-up regulator reduces
    the control pressure to a degree dependent
    upon engine temperature and thus
    causes the metering slits to open further
    (Figure 25).
    At the beginning of the warm-up period
    which directly follows the cold start, some
    of the injected fuel still condenses on the
    cylinder walls and in the intake ports.
    This can cause combustion misses to
    occur. For this reason, the air-fuel mixture
    must be enriched during the warmup
    (ì < 1.0). This enrichment must be
    continuously reduced along with the rise
    in engine temperature in order to prevent
    the mixture being over-rich when higher
    engine temperatures have been reached.
    The warm-up regulator (control-pressure
    regulator) is the component which carries
    out this type of mixture control for the
    warm-up period by changing the control
    Warm-up regulator
    The change of the control pressure is
    effected by the warm-up regulator which
    is fitted to the engine in such a way that it
    ultimately adopts the engine temperature.
    An additional electrical heating system
    enables the regulator to be matched
    precisely to the engine characteristic.
    Warm-up regulator
    a With the engine
    b With the engine at
    1 Valve diaphragm,
    2 Return,
    3 Control pressure
    (from the mixturecontrol
    4 Valve spring,
    5 Bimetal spring,
    6 Electrical heating.

    6 5 4
    2 3

    Fig. 25
    The warm-up regulator comprises a
    spring-controlled flat seat (diaphragmtype)
    valve and an electrically heated
    bimetal spring (Figure 25).
    In cold condition, the bimetal spring
    exerts an opposing force to that of the
    valve spring and, as a result, reduces the
    effective pressure applied to the underside
    of the valve diaphragm. This means
    that the valve outlet cross-section is
    slightly increased at this point and more
    fuel is diverted out of the control-pressure
    circuit in order to achieve a low
    control pressure. Both the electrical
    heating system and the engine heat the
    bimetal spring as soon as the engine is
    cranked. The spring bends, and in doing
    so reduces the force opposing the valve
    spring which, as a result, pushes up the
    diaphragm of the flat-seat valve. The
    valve outlet cross-section is reduced and
    the pressure in the control-pressure
    circuit rises.
    Warm-up enrichment is completed when
    the bimetal spring has lifted fully from the
    valve spring. The control pressure is now
    solely controlled by the valve spring and
    maintained at its normal level. The control
    pressure is about 0.5 bar at cold start
    and about 3.7 bar with the engine at
    operating temperature (Figure 26).
    Idle stabilization
    In order to overcome the increased
    friction in cold condition and to guarantee
    smooth idling, the engine receives more
    air-fuel mixture during the warm-up
    phase due to the action of the auxiliary
    air device.
    When the engine is cold, the frictional
    resistances are higher than when it is at
    operating temperature and this friction
    must be overcome by the engine during
    idling. For this reason, the engine is
    allowed to draw in more air by means of
    the auxiliary-air device which bypasses
    the throttle valve. Due to the fact that this
    auxiliary air is measured by the air-flow
    sensor and taken into account for fuel
    metering, the engine is provided with
    more air-fuel mixture. This results in idle
    stabilization when the engine is cold.
    Auxiliary-air device
    In the auxiliary-air device, a perforated
    plate is pivoted by means of a bimetal
    spring and changes the open crosssection
    of a bypass line. This perforated
    plate thus opens a correspondingly large
    cross-section of the bypass line, as a
    function of the temperature, and this
    cross-section is reduced with increasing
    engine temperature and is ultimately
    closed. The bimetal spring also has an
    electrical heating system which permits
    the opening time to be restricted dependent
    upon the engine type. The in-
    Warm-up regulator characteristics at various operating temperatures
    Enrichment factor 1.0 corresponds to fuel metering with the engine at operating temperature.
    0 30 60 90 120 150 s
    Enrichment factor
    Time after starting
    0 30 60 90 120 150 s
    Control pressure
    Time after starting
    Fig. 26
    stallation location of the auxiliary-air device
    is selected such that it assumes the
    engine temperature. This guarantees
    that the auxiliary-air device only functions
    when the engine is cold (Figure 27).
    Full-load enrichment
    Engines operated in the part-load range
    with a very lean mixture require an enrichment
    during full-load operation, in
    addition to the mixture adaptation resulting
    from the shape of the air funnel.
    This extra enrichment is carried out by a
    specially designed warm-up regulator.
    This regulates the control pressure depending
    upon the manifold pressure
    (Figures 28 and 30).
    This model of the warm-up regulator
    uses two valve springs instead of one.
    The outer of the two springs is supported
    on the housing as in the case with the
    normal-model warm-up regulator. The
    inner spring however is supported on a
    diaphragm which divides the regulator
    into an upper and a lower chamber. The
    manifold pressure which is tapped via a
    hose connection from the intake manifold
    downstream of the throttle valve acts in
    the upper chamber. Depending upon the
    model, the lower chamber is subjected to
    atmospheric pressure either directly or
    by means of a second hose leading to the
    air filter.
    Due to the low manifold pressure in the
    idle and part-load ranges, which is also
    present in the upper chamber, the diaphragm
    lifts to its upper stop. The inner
    spring is then at maximum pretension.
    The pretension of both springs, as a
    result, determines the particular control
    pressure for these two ranges. When the
    throttle valve is opened further at full
    load, the pressure in the intake manifold
    increases, the diaphragm leaves the
    upper stops and is pressed against the
    lower stops.
    The inner spring is relieved of tension
    and the control pressure reduced by the
    specified amount as a result. This results
    in mixture enrichment.
    Auxiliary-air device
    1 Electrical connection, 2 Electrical heating,
    3 Bimetal spring, 4 Perforated plate.
    Dependence of the control pressure
    on engine load
    Acceleration response
    Behavior of the K-Jetronic when the throttle valve
    is suddenly opened.
    1 2 3 4
    Control pressure
    Engine load
    Full load
    Idle and part load
    Engine speed Sensor-plate travel
    0 0.1 0.2 0.3 0.4 s
    Time t
    Fig. 28
    Fig. 29
    Fig. 29
    UMK1659E UMK0019E UMK0127Y
    Acceleration response
    The good acceleration response is a result
    of “overswing” of the air-flow sensor
    plate (Figure 29).
    Transitions from one operating condition
    to another produce changes in the mixture
    ratio which are utilized to improve
    If, at constant engine speed, the throttle
    valve is suddenly opened, the amount
    of air which enters the combustion
    chamber, plus the amount of air which is
    needed to bring the manifold pressure
    up to the new level, flow through the
    airflow sensor. This causes the sensor
    plate to briefly “overswing” past the fully
    opened throttle point. This “overswing”
    results in more fuel being metered to the
    engine (acceleration enrichment) and
    ensures good acceleration response.
    Warm-up regulator
    with full-load
    a During idle and part
    b During full load.
    1 Electrical heating,
    2 Bimetal spring,
    3 Vacuum connection
    (from intake manifold),
    4 Valve diaphragm,
    5 Return to fuel tank,
    6 Control pressure
    (from fuel distributor),
    7 Valve springs,
    8 Upper stop,
    9 To atmospheric pressure,
    10 Diaphragm,
    11 Lower stop.

    1 2 3 4 5 6

    11 10


    Fig. 30
    Supplementary functions
    Overrun fuel cutoff
    Smooth fuel cutoff effective during overrun
    responds as a function of the engine
    speed. The engine-speed information is
    provided by the ignition system. Intervention
    is via an air bypass around the
    sensor plate. A solenoid valve controlled
    by an electronic speed switch opens the
    bypass at a specific engine speed. The
    sensor plate then reverts to zero position
    and interrupts fuel metering. Cutoff of the
    fuel supply during overrun operation
    permits the fuel consumption to be
    reduced considerably not only when
    driving downhill but also in town traffic.
    Engine speed limiting
    The fuel supply can be cut off to limit the
    maximum permissible engine speed.
    Lambda closed-loop control
    Open-loop control of the air-fuel ratio is
    not adequate for observing extremely
    low exhaust-gas limit values. The lambda
    closed-loop control system required for
    operation of a three-way catalytic converter
    necessitates the use of an electronic
    control unit on the K-Jetronic. The
    important input variable for this control
    unit is the signal supplied by the lambda
    In order to adapt the injected fuel quantity
    to the required air-fuel ratio with ì = 1, the
    Additional components for lambda closed-loop control
    1 Lambda sensor,
    2 Lambda closed-loop controller,
    3 Frequency valve (variable restrictor),
    4 Fuel distributor,
    5 Lower chambers of the differentialpressure
    6 Metering slits,
    7 Decoupling restrictor
    (fixed restrictor),
    8 Fuel inlet,
    9 Fuel return line.
    Fig. 31

    5 7
    10 6 7 10
    8 9
    pressure in the lower chambers of the
    fuel distributor is varied. If, for instance,
    the pressure in the lower chambers is
    reduced, the differential pressure at the
    metering slits increases, whereby the
    injected fuel quantity is increased. In
    order to permit the pressure in the lower
    chambers to be varied, these chambers
    are decoupled from the primary pressure
    via a fixed restrictor, by comparison with
    the standard K-Jetronic fuel distributor.
    A further restrictor connects the lower
    chambers and the fuel return line.
    This restrictor is variable: if it is open, the
    pressure in the lower chambers can drop.
    If it is closed, the primary pressure builds
    up in the lower chambers. If this restrictor
    is opened and closed in a fast rhythmic
    succession, the pressure in the lower
    chambers can be varied dependent upon
    the ratio of closing time to opening time.
    An electromagnetic valve, the frequency
    valve, is used as the variable restrictor. It
    is controlled by electrical pulses from the
    lambda closed-loop controller.
    1 Fuel accumulator, 2 Electric fuel pump, 3 Fuel filter, 4 Warm-up regulator, 5 Mixture-control unit with
    air-flow sensor and fuel distributor, 6 Cold-start valve, 7 Thermo-time switch, 8 Injection valves,
    9 Auxiliary-air device, 10 Electronic control relay.
    Components of the K-Jetronic system
    4 5
    1 2
    Fig. 32
    Exhaust-gas treatment
    Lambda sensor
    The Lambda sensor inputs a voltage
    signal to the ECU which represents
    theinstantaneous composition of the airfuel
    The Lambda sensor is installed in the
    engine exhaust manifold at a point which
    maintains the necessary temperature for
    the correct functioning of the sensor over
    the complete operating range of the
    The sensor protrudes into the exhaustgas
    stream and is designed so that the
    outer electrode is surrounded by exhaust
    gas, and the inner electrode is connected
    to the atmospheric air.
    Basically, the sensor is constructed from
    an element of special ceramic, the surface
    of which is coated with microporous
    platinum electrodes. The operation of the
    sensor is based upon the fact that
    ceramic material is porous and permits
    diffusion of the oxygen present in the air
    (solid electrolyte). At higher temperatures,
    it becomes conductive, and if the
    oxygen concentration on one side of the
    electrode is different to that on the other,
    then a voltage is generated between the
    electrodes. In the area of stoichiometric
    airfuel mixture (ì = 1.00), a jump takes
    place in the sensor voltage output curve.
    This voltage represents the measured
    The ceramic sensor body is held in a
    threaded mounting and provided with a
    protective tube and electrical connections.
    The surface of the sensor ceramic
    body has a microporous platinum layer
    which on the one side decisively influences
    the sensor characteristic while on
    the other serving as an electrical contact.
    A highly adhesive and highly porous
    ceramic coating has been applied over
    the platinum layer at the end of the
    ceramic body that is exposed to the exhaust
    gas. This protective layer prevents
    the solid particles in the exhaust gas from
    eroding the platinum layer. A protective
    metal sleeve is fitted over the sensor
    on the electrical connection end and
    crimped to the sensor housing. This
    sleeve is provided with a bore to ensure
    pressure compensation in the sensor interior,
    and also serves as the support for
    the disc spring. The connection lead is
    crimped to the contact element and is led
    through an insulating sleeve to the outside
    of the sensor. In order to keep
    combustin deposits in the exhaust gas
    away from the ceramic body, the end of
    the exhaust sensor which protrudes into
    the exhaust-gas flow is protected by a
    special tube having slots so designed
    that the exhaust gas and the solid particles
    entrained in it do not come into
    direct contact with the ceramic body.
    In addition to the mechanical protection
    thus provided, the changes in sensor
    temperature during transition from one
    operating mode to the other are effectively
    The voltage output of the ì sensor, and
    its internal resistance, are dependent
    upon temperature. Reliable functioning
    of the sensor is only possible with
    exhaust-gas temperatures above 360°C
    (unheated version), and above 200°C
    (heated version).
    Control range of the lambda sensor and
    reduction of pollutant concentrations in
    Without catalytic aftertreatment
    With catalytic aftertreatment
    0.9 0.95 1.0 1.05 1.1
    Excess-air factor l
    Exhaust emissions, sensor voltage
    l-control range
    Voltage curve
    of l sensor
    Fig. 33
    Heated Lambda oxygen sensor
    To a large extent, the design principle of
    the heated Lambda sensor is identical to
    that of the unheated sensor.
    The active sensor ceramic is heated internally
    by a ceramic heating element
    with the result that the temperature of the
    ceramic body always remains above the
    function limit of 350°C.
    The heated sensor is equipped with a
    protective tube having a smaller opening.
    Amongst other things, this prevents the
    sensor ceramic from cooling down when
    the exhaust gas is cold. Among the advantages
    of the heated Lambda sensor
    are the reliable and efficient control at low
    exhaust-gas temperatures (e.g. at idle),
    the minimum effect of exhaust-gas temperature
    variations, the rapid coming into
    effect of the Lambda control following
    engine start, short sensor-reaction time
    which avoids extreme deviations from the
    ideal exhaust-gas composition, versatility
    regarding installation because the sensor
    is now independent of heating from its
    Lambda closed-loop control circuit
    By means of the Lambda closed-loop
    control, the air-fuel ratio can be maintained
    precisely at ì= 1.00.
    The Lambda closed-loop control is an
    add-on function which, in principle, can
    supplement every controllable fuelmanagement
    system. It is particularly
    suitable for use with Jetronic gasolineinjection
    systems or Motronic. Using the
    closed-loop control circuit formed with
    the aid of the Lambda sensor, deviations
    from a specified air-fuel ratio can be
    detected and corrected. This control
    principle is based upon the measurement
    of the exhaust-gas oxygen by the
    Lambda sensor. The exhaust-gas oxygen
    is a measure for the composition of
    the air-fuel mixture supplied to the engine.
    The Lambda sensor acts as a probe
    in the exhaust pipe and delivers the
    information as to whether the mixture is
    richer or leaner than ì = 1.00.
    In case of a deviation from this ì = 1.00
    figure, the voltage of the sensor output
    signal changes abruptly. This pronounced
    change is evaluated by the ECU which is
    provided with a closed-loop control circuit
    for this purpose. The injection of fuel to
    the engine is controlled by the fuelmanagement
    system in accordance with
    the information on the composition of the
    air-fuel mixture received from the Lambda
    sensor. This control is such that an airfuel
    ratio of ì = 1 is achieved. The sensor
    voltage is a measure for the correction of
    the fuel quantity in the air-fuel mixture.
    Location of the lambda sensor in the exhaust
    pipe (schematic)
    1 Sensor ceramic, 2 Electrodes, 3 Contact,
    4 Electrical contacting to the housing,
    5 Exhaust pipe, 6 Protective ceramic coating
    (porous), 7 Exhaust gas, 8 Air. U voltage.
    Positioning of the lambda sensor
    in a dual exhaust system

    Fig. 34 Fig. 35
    The signal which is processed in the
    closed-loop control circuit is used to
    control the actuators of the Jetronic installation.
    In the fuel-management system
    of the K-Jetronic (or carburetor system),
    the closed-loop control of the mixture
    takes place by means of an additional
    control unit and an electromechanical
    actuator (frequency valve). In this manner,
    the fuel can be metered so precisely that
    depending upon load and engine speed,
    the air-fuel ratio is an optimum in all
    operating modes. Tolerances and the
    ageing of the engine have no effect whatsoever.
    At values above ì = 1.00, more
    fuel is metered to the engine, and at
    values below ì = 1.00, less. This continuous,
    almost lag-free adjustment of the
    air-fuel mixture to ì = 1.00, is one of the
    prerequisites for the efficient aftertreatment
    of the exhaust gases by the
    downstream catalytic converter.
    Control functions at various
    operating modes
    The Lambda sensor must have reached
    a temperature of above 350 °C before it
    outputs a reliable signal. Until this temperature
    has been reached, the closedloop
    mode is suppressed and the air-fuel
    mixture is maintained at a mean level by
    means of an open-loop control. Starting
    enrichment is by means of appropriate
    components similar to the Jetronic
    installations not equipped with Lambda
    Acceleration and full load (WOT)
    The enrichment during acceleration can
    take place by way of the closed-loop
    control unit. At full load, it may be necessary
    for temperature and power reasons
    to operate the engine with an air-fuel ratio
    which deviates from the ì = 1 figure.
    Similar to the acceleration range, a sensor
    signals the full-load operating mode
    to the closed-loop control unit which then
    switches the fuel-injection to the openloop
    mode and injects the corresponding
    amount of fuel.
    Deviations in air-fuel mixture
    The Lambda closed-loop control operates
    in a range between ì = 0.8…1.2 in
    which normal disturbances (such as the
    effects of altitude) are compensated for
    by controlling ì to 1.00 with an accuracy
    of ±1 %. The control unit incorporates a
    circuit which monitors the Lambda
    sensor and prevents prolonged marginal
    operation of the closed-loop control. In
    such cases, open-loop control is selected
    and the engine is operated at a mean
    Heated lambda sensor
    1 Sensor housing, 2 Protective ceramic tube, 3 Connection cable, 4 Protective tube with slots, 5 Active
    sensor ceramic, 6 Contact element, 7 Protective sleeve, 8 Heater, 9 Clamp terminals for heater.
    1 2 3
    4 5 6 7 8 9 10
    Fig. 36
    Lambda closed control-loop
    The Lambda closed control-loop is superimposed upon the air-fuel mixture control. The fuel quantity to
    be injected, as determined by the air-fuel mixture control, is modified by the Lambda closed-loop control
    in order to provide optimum combustion.
    Ul Lambda-sensor signal
    View of the unheated (front) and heated lambda sensors
    Differential pressure
    (manipulated variable)
    Engine (controlled system)
    Lambda closed-loop control
    in the Motronic ECU
    Exhaust-gas oxygen
    Frequency valve
    (final controlling
    Fig. 38
    Fig. 37
    UMK0282Y UMK0307E
    Electrical circuitry
    If the engine stops but the ignition remains
    switched on, the electric fuel
    pump is switched off.
    The K-Jetronic system is equipped with
    a number of electrical components, such
    as electric fuel pump, warm-up regulator,
    auxiliary-air device, cold-start valve and
    thermo-time switch. The electrical supply
    to all of these components is controlled by
    the control relay which, itself, is switched
    by the ignition and starting switch.
    Apart from its switching functions, the
    control relay also has a safety function.
    A commonly used circuit is described
    When cold-starting the engine, voltage is
    applied to the cold-start valve and the
    thermo-time switch through terminal 50
    of the ignition and starting switch. If the
    cranking process takes longer than
    between 8 and 15 seconds, the thermotime
    switch switches off the cold-start
    valve in order that the engine does not
    “flood”. In this case, the thermo-time
    switch performs a time-switch function.
    If the temperature of the engine is above
    approximately +35 °C when the starting
    process is commenced, the thermo-time
    switch will have already open-circuited
    the connection to the start valve which,
    Circuit without
    voltage applied
    1 Ignition and starting
    2 Cold-start valve,
    3 Thermo-time switch,
    4 Control relay,
    5 Electric fuel pump,
    6 Warm-up regulator,
    7 Auxiliary-air device.
    Starting (with the
    engine cold)
    Cold-start valve and
    thermo-time switch are
    switched on. The engine
    turns (pulses are
    taken from terminal 1 of
    the ignition coil). The
    control relay, electric
    fuel pump, auxiliary-air
    device and warm-up
    regulator are switched
    2 3 4 5 6 7
    15 15 87
    1 31
    2 3 4 5 6 7
    15 15 87
    1 31
    Fig. 39
    Fig. 40
    UMK0197Y UMK0196Y
    consequently, does not inject extra fuel.
    In this case, the thermo-time switch
    functions as a temperature switch.
    Voltage from the ignition and starting
    switch is still present at the control relay
    which switches on as soon as the engine
    runs. The engine speed reached when
    the starting motor cranks the engine is
    high enough to generate the “engine
    running” signal which is taken from the
    ignition pulses coming from terminal 1 of
    the ignition coil. An electronic circuit in
    the control relay evaluates these pulses.
    After the first pulse, the control relay is
    switched on and applies voltage to the
    electric fuel pump, the auxiliary-air
    device and the warm-up regulator. The
    control relay remains switched on as long
    as the ignition is switched on and the
    ignition is running. If the pulses from
    terminal 1 of the ignition coil stop because
    the engine has stopped turning,
    for instance in the case of an accident,
    the control relay switches off approximately
    1 second after the last pulse is
    This safety circuit prevents the fuel pump
    from pumping fuel when the ignition is
    switched on but the engine is not turning.
    Ignition on and engine
    Control relay, electric
    fuel pump, auxiliary-air
    device and warm-up
    regulator are switched
    Ignition on
    but engine stopped
    No pulses can be taken
    from terminal 1 of the
    ignition coil. The control
    relay, electric fuel
    pump, auxiliary-air
    device and warm-up
    regulator are switched
    2 3 4 5 6 7
    15 15 87
    1 31
    2 3 4 5 6 7
    15 15 87
    1 31
    Fig. 41
    Fig. 42
    UMK0199Y UMK0198Y
    Workshop testing techniques
    Bosch customer service
    Customer service quality is also a measure
    for product quality. The car driver has
    more than 10,000 Bosch Service Agents
    at his disposal in 125 countries all over the
    world. These workshops are neutral and
    not tied to any particular make of vehicle.
    Even in sparsely populated and remote
    areas of Africa and South America the
    driver can rely on getting help very quickly.
    Help which is based upon the same
    quality standards as in Germany, and
    which is backed of course by the identical
    guarantees which apply to customer-service
    work all over the world. The data and
    performance specs for the Bosch systems
    and assemblies of equipment are precisely
    matched to the engine and the vehicle.
    In order that these can be checked in the
    workshop, Bosch developed the appropriate
    measurement techniques, test equipment,
    and special tools and equipped all
    its Service Agents accordingly.
    Testing techniques for K-Jetronic
    Apart from the regular replacement of the
    fuel filter as stipulated by the particular
    vehicle’s manufacturer, the K-Jetronic
    gasoline-injection system requires no
    special maintenance work.
    In case of malfunctions, the workshop
    expert has the following test equipment,
    together with the appropriate test specs,
    at his disposal:
    – Injector tester
    – Injected-quantity comparison tester
    – Pressure-measuring device, and
    – Lambda closed-loop control tester (only
    needed if Lambda control is fitted).
    Together with the relevant Test Instructions
    and Test Specifications in a variety of
    different languages, this uniform testing
    technology is available throughout the
    world at the Bosch Service Agent workshops
    and at the majority of the workshops
    belonging to the vehicle manufacturers.
    Purposeful trouble-shooting and
    technically correct repairs cannot be performed
    at a reasonabe price without this
    equipment. It is therefore inadvisable for
    the vehicle owner to attempt to carry out
    his own repairs.
    Injector tester
    The injector tester (Fig. 43) was developed
    specifically for testing the K- and
    KE-Jetronic injectors when removed
    from the engine. The tester checks all the
    functions of the injector which are essential
    for correct engine running:
    – Opening pressure,
    – Leakage integrity,
    – Spray shape,
    – Chatter.
    Those injectors whose opening pressure
    is outside tolerance are replaced. For the
    leak test, the pressure is slowly increased
    up to 0.5 bar below the opening
    pressure and held at this point. Within
    60 secs, no droplet of fuel is to form at the
    injector. During the chatter test, the
    injector must generate a “chattering”
    noise without a fuel droplet being formed.
    Serviceable injectors generate a fully
    atomized spray pattern. “Pencil” jets and
    “bundled” jets are not to form.
    Injected-quantity comparison tester
    Without removing the fuel distributor from
    the vehicle, a comparitive measurement is
    made to determine the differences in the
    delivered quantities from the various fueldistributor
    outlets (this applies to all engines
    of up to maximum eight cylinders.
    Injector tester
    Fig. 43 UMK1494Y
    Fig. 44). And since the test is performed
    using the original injectors it is possible to
    ascertain at the same time whether any
    scatter in the figures results from the fuel
    distributor itself or from the injectors.
    The tester’s small measuring tubes serve
    for idle measurement and its larger
    measuring tubes for part-load or fullload
    Connection to the fuel distributor is by
    means of eight hoses. The injectors are
    pulled out of their mountings on the
    engine and inserted in the automatic
    couplings at the ends of the hoses. Each
    automatic coupling incorporates a pushup
    valve which prevents fuel escaping on
    hoses which are not connected (e.g. on
    6-cylinder systems. Fig. 44). A further
    hose returns the fuel to the tank.
    Pressure-measuring device
    This is used to measure all the pressures
    which are important for correct K-Jetronic
    – Primary (system) pressure: Provides
    information on the performance of the
    fuel-supply pump, on fuel-filter flow
    resistance, and on the condition of the
    primary-pressure regulator.
    – Control pressure: Important for assessment
    of all operating conditions
    (for instance: Cold/warm engine; part
    load/full load; fuel-enrichment functions,
    occasionally pressure at high
    – Leakage integrity of the complete
    system. This is particularly important
    with regard to the cold-start and hotstart
    behavior. Automatic couplings in
    the hoses prevent the escape of fuel.
    Lambda closed-loop-control tester
    On K-Jetronic systems with Lambda
    closed-loop control, this tester serves to
    check the duty factor of the Lambda-sensor
    signal (using simulation of the “rich”/
    “lean” signal), and the “open-loop/closedloop
    control function”. Special adapter
    lines are available for connection to the
    Lambda-sensor cable of the various vehicle
    models. Measured values are shown
    on an analog display.
    Injected-quantity comparison tester (connected to a 6-cylinder installation)
    1 Fuel-distributor injection lines,
    2 Injectors,
    3 Automatic couplings,
    4 Comparison-tester hoses,
    5 Small measuring tube,
    6 Large measuring tube,
    7 Return line to fuel tank.
    1 2 3 4 5 6 7 8
    2 3 4
    5 6
    Fig. 44
    1 987 722 159
    The Program Order Number
    Gasoline-engine management
    Emission Control (for Gasoline Engines) 1 987 722 102
    Gasoline Fuel-Injection System K-Jetronic 1 987 722 159
    Gasoline Fuel-Injection System KE-Jetronic 1 987 722 101
    Gasoline Fuel-Injection System L-Jetronic 1 987 722 160
    Gasoline Fuel-Injection System Mono-Jetronic 1 987 722 105
    Ignition 1 987 722 154
    Spark Plugs 1 987 722 155
    M-Motronic Engine Management 1 987 722 161
    ME-Motronic Engine Management 1 987 722 178
    Diesel-engine management
    Diesel Fuel-Injection: An Overview 1 987 722 104
    Diesel Accumulator Fuel-Injection System
    Common Rail CR 1 987 722 175
    Diesel Fuel-Injection Systems
    Unit Injector System / Unit Pump System 1 987 722 179
    Radial-Piston Distributor Fuel-Injection
    Pumps Type VR 1 987 722 174
    Diesel Distributor Fuel-Injection Pumps VE 1 987 722 164
    Diesel In-Line Fuel-Injection Pumps PE 1 987 722 162
    Governors for Diesel In-Line Fuel-Injection Pumps 1 987 722 163
    Automotive electrics/Automotive electronics
    Alternators 1 987 722 156
    Batteries 1 987 722 153
    Starting Systems 1 987 722 170
    Electrical Symbols and Circuit Diagrams 1 987 722 169
    Lighting Technology 1 987 722 176
    Safety, Comfort and Convenience Systems 1 987 722 150
    Driving and road-safety systems
    Compressed-Air Systems for Commercial
    Vehicles (1): Systems and Schematic Diagrams 1 987 722 165
    Compressed-Air Systems for Commercial
    Vehicles (2): Equipment 1 987 722 166
    Brake Systems for Passenger Cars 1 987 722 103
    ESP Electronic Stability Program 1 987 722 177
    Automotive electric/electronic systems
    Safety, Comfort and
    Convenience Systems
    Technical Instruction
    ¾ ®
    Automotive Electric/Electronic Systems
    Lighting Technology
    Technical Instruction
    ¾ ®
    Vehicle safety systems for passenger cars
    ESP Electronic Stability Program
    Technical Instruction
    ¾ ®
    Engine management for diesel engines
    Radial-Piston Distributor
    Fuel-injection Pumps Type VR
    Technical Instruction
    ¾ ®
    Electronic engine management for diesel engines
    Diesel Acumulator Fuel-Injection
    System Common Rail
    Technical Instruction
    ¾ ®
    Engine management for spark-ignition engines
    Emission Control
    Technical Instruction
    ¾ ®
    Gasoline-engine management
    Engine Management
    Technical Instruction
    ¾ ®
    Engine management for spark-ignition engines
    Spark Plugs
    Technical Instruction
    ¾ ®
    Brake systems for passenger cars
    Brake Systems
    Technical Instruction
    ¾ ®

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