444 The Motor Vehicle
of 0.1 bar– with 4.6 bar in the upper chamber – is still maintained since a higher
pressure would open the port wider, allowing the fuel to flow through at an
even higher rate, and a lower one would close it. The deflection of the
diaphragm is in fact only a few hundredths of a millimetre.
From this it can be seen that the injection valve has no metering function.
It is closed by a spring and opens automatically when the pressure in the
delivery pipe rises above 3.3 bar. At this pressure the fuel is finely atomised
as it passes through the discharge nozzle into the engine inlet valve port.
The only adjustments that can be made to this system in service are those
of the engine idling speed and mixture. For adjustment of idling speed, there
is a screw that restricts the flow of air through a passage that by-passes the
throttle valve when it is closed. The greater the degree of restriction of
course, the slower is the idling speed. To increase idling speed, therefore, the
screw should be turned anti-clockwise.
The idling mixture strength is adjusted by another screw, which acts on
the arm by means of which the motion of the air sensor plate is transmitted
to the control plunger. Access can be gained for this adjustment, using a
screwdriver, without any dismantling of the mixture-control unit. As can be
seen from Fig. 12.11, the idling mixture screw is on the end of a lever
swinging about the same pivot as, and approximately parallel to, the arm that
carries the air sensor plate. The end of the screw seats on that arm so, when
it is screwed clockwise, it increases the angle subtended between the smaller
lever and the arm. This raises the control plunger slightly, thus supplying
more fuel to the injectors and therefore enriching the mixture.
12.14 Bosch KE-Jetronic system
The KE-Jetronic system, Fig. 12.20, is similar to the K-Jetronic except that
it has a simple diaphragm-type fuel pressure regulator, in place of the warm-
up regulator, to maintain a constant primary pressure above the control plunger
in the fuel distributor of Fig. 12.17. Another change is the flange-mounting of
an electro-hydraulic pressure actuator on the fuel distributor, to regulate the

pressure in the supply to the lower chambers of the differential pressure
valves. Thus, whereas in the K-Jetronic the mixture enrichment is effected
(a) (b)
Fig. 12.19 Metering slit and diaphragm. (a) At high rate of fuel flow, (b) at low rate
of fuel flow. The control plunger is that on the right in each diaphragm
445Petrol injection systems
1
2
3
4
5
6
9
8
12
11
15
14
13
10
7
1 Injector 9 Electric fuel pump
2 Cold start injector 10 Electronic control unit
3 Fuel distributor 11 Idle by-pass valve actuator
4 Electro-hydraulic pressure actuator 12 Throttle position switch
5 Fuel pressure regulator 13 Lambda sensor
6 Air-flow meter 14 Engine temperature sensor
7 Filter 15 Thermo time switch
8 Fuel accumulator
Fig. 12.20 Bosch KE-Jetronic system

by regulating the pressure above the control plunger, this function is performed
in the KE by regulating the pressure input to the lower chambers and, moreover,
not only for cold starting and warm-up but also for all other situations.
Yet another addition is a potentiometer on the air-flow sensor lever. Its function
is to signal to the electronic control the rate of air flow into the engine.
Additional input signals to the electronic control include engine temperature,
engine speed (from the ignition system), idle, overrun and full-throttle
signals (from the throttle position switch), exhaust content (from the lambda
sensor), atmospheric pressure, and an engine starting signal from the ignition
switch. The output from the electronic control goes to the electro-hydraulic
pressure actuator.
Fuel is drawn from the tank by the pump and delivered through the hydraulic
accumulator to the filter and thence to the electro-hydraulic pressure actuator,
in which it is directed through a nozzle on to a plate. The clearance between
the mouth of the nozzle and the plate is varied by an axial force exerted by
an electro-magnet on a pole-piece on the plate. This clearance is therefore
determined by the magnitude of the electric current passing through the
windings of the electro-magnet, which in turn is regulated by the electronic
control. During overrun, it can totally cut off the supply of fuel.
446 The Motor Vehicle
12.15 Bosch L-Jetronic system
In the L-Jetronic system, Fig. 12.21, the electronic control unit performs the
same function as the mixture control unit of the K system. It does this,
however, by controlling the duration of opening of the solenoid-actuated
valves in the injectors. The advantage of electronic control is that there are
fewer mechanical components liable to wear or to stick and thus to malfunction.
Moreover, ultimately, more accurate control is possible because the system
can be made more easily to respond to a wider range of variables than when
a mechanical system is used.
Because the injectors are solenoid actuated, Fig. 12.22, lower delivery

pressures are possible than those needed to open the pressure-actuated delivery
valves of the K system. Another advantage is that delivery can be made
through all the valves simultaneously, which means that the injection system
can be simpler than if each had to be opened individually. Actually, to ensure
that the distribution of fuel is uniform, to all cylinders, half the required
amount of fuel is injected into each port twice, over two separate intervals,
during each four-stroke cycle – that is, for each 360° rotation of the camshaft,
Fig. 12.23.
The start of each injection pulse is signalled to the electronic control unit
by the contacts in the ignition distributor. However, the control unit has to
2
6
9
1
10
11
5
4
7
8
3
Pressure in intake Atmospheric Fuel Coolant
manifold (
p
1
) pressure (
p
0
)
1 Electronic control unit 5 Thermo-time switch 9 Pressure regulator valve

2 Injection valve 6 Start valve 10 Auxiliary-air device
3 Air-flow sensor 7 Electric pump 11 Throttle-valve switch
4 Temperature sensor 8 Fuel filter 12 Relay set
Fig. 12.21 Bosch L-Jetronic system
12
447Petrol injection systems
respond to only every second signal from the contact breaker in a four-
cylinder engine and every third in a six-cylinder unit – since they have four
and six sparks per cycle whereas only two injections per cylinder are required
in each case.
1
2
3
4
5
1 Nozzle valve
2 Solenoid armature
3 Solenoid winding
4 Electrical connection
5 Filter
Fig. 12.22 Cross-section of the injection valve
Suction stroke Instant of ignition
1
3
4
2
Cylinder
Operating cycle
1
Distributor

contact
points
Engine speed
2
Pulse shaper
Engine speed
Frequency
divider
Injection cycle
3
4
Charging
operation
1
2
n
5
Discharging
operation
Influence of compen-
sation factors
1 Basic quantity
(Air-flow sensor)
2 Temperature
3 Operating condition
6
Injection pulse
duration of
injection
Amount of fuel

injected
1 2 3
t
i
0° 180° 360° 540° 720° CS
Fig. 12.23 Pulse diagram
448 The Motor Vehicle
Although the basic signal determining the duration of injection is that
from the swinging gate type air flow sensor, Section 12.9, it has to be modified
by a number of other signals received by the electronic control. One is
engine speed, which is signalled by the frequency of operation of the ignition
contact breaker. A throttle valve-actuated switch indicates whether enrichment
is needed, for either full load or idling. As in the K system, there is a
temperature sensor, but it influences the duration of injection instead of the
pressure. It is necessary because the density and therefore mass of air drawn
into the cylinders is greater in cold than in hot conditions. An enrichment
device for acceleration is unnecessary in either system since the air flow
sensor gives its signal in advance of acceleration.
A solenoid-actuated start valve comes into operation for cold starting.
This is the same as in the K system, as also is the auxiliary air device for by-
passing the throttle valve to compensate for the high friction losses. Here,
however, there is a relay set. When the ignition is switched on, this relay set
switches the battery voltage to the electric fuel pump, start valve, thermo-
time switch for switching off the start valve, and auxiliary air device. When
the engine starts, the power supply for the pump and auxiliary air device is
maintained through a contact actuated by the air sensor. If, on the other hand,
the engine fails to start, a thermo-time switch interrupts the circuit to the
solenoid-actuated start valve, to avoid flooding the cylinders.
With no control-valve unit, the fuel supply is simpler than before: it
passes from the pump through a filter to a pressure-regulating valve and

thence directly to the injector and start valve. With such a simple and direct
supply a fuel accumulator is unnecessary.
As can be seen from Fig. 12.25, the fuel pressure regulator valve is of
conventional design. The fuel flows radially in one side and out the other,
while fuel in excess of requirements passes out through the connection at the
top of the unit and thence back to the tank. With the L-Jetronic system, the
fuel delivery pressure is either 2.5 or 3 bar, according to the type of engine.
It is maintained at its set value by a spring-loaded diaphragm, which causes
a valve to tend to seat on the port for the return line to the tank. Any increase
in pressure pushes the diaphragm down and opens this port. To avoid variations
in the back-pressure on the nozzles due to changing induction manifold
1
2
3
4
57
1 Mixture adjustment screw for
the idle range
2 Air-flow sensor flap
3 Non-return valve
4 Air-temperature sensor
5 Electrical connections
6 Damping chamber
7 Compensation flap
6
Fig. 12.24 Cross-section of the air-flow sensor
449Petrol injection systems
pressure, a pipeline connection is taken from the manifold to the chamber
below the diaphragm.
Bosch also produce a petrol injection system in which the engine load

signal is obtained by sensing the depression in the inlet manifold. This is the
D-Jetronic system. It will not be described here, however, since the L system
is the more advanced one and therefore of greater importance. In any case,
wear of the engine causes manifold depression characteristics to change.
12.16 Bosch LH-Jetronic system
All components of the LH are virtually identical to those of the L-Jetronic
system, except for the electronic control unit and the substitution of a hot-
wire, air-mass-flow meter (Section 12.10) for the volume-flow meter. A
major advance made more easily feasible by the use of the hot-wire system
is the use of a digital instead of analogue electronic control system, the
former being potentially much more flexible. Other advantages of the LH
system are negligible resistance to air flow and absence of moving parts.
The incoming air flows past an electrically heated platinum wire, the
temperature of which is maintained constant by using the wire as one arm of
a Wheatstone bridge circuit and varying a resistance to balance the bridge.
Since the quantity of heat removed from the wire is a function of not only the
velocity but also the density of the air flowing past it, the increase in current
needed to maintain a constant temperature is a measure of the mass flow of
the air. A voltage signal taken from across a resistance through which this
current is passed is transmitted to the control unit. Among the other advantages
is that the hot wire compensates automatically for changes in altitude.
Other signals required include engine speed, throttle position, and ambient
air temperature. An engine load–speed map is stored in the memory of the
electronic control system which, taking into account all the other input signals,
can in all circumstances accurately regulate the air : fuel ratio for optimum
power output, fuel consumption, and exhaust emissions.
During idling the air mass flow is small so, in this condition, the air : fuel
ratio is set by a potentiometer. Another factor is that the surface of the wire
2
1

7
3
4
5
6
1 Fuel through-flow
2 Return line to fuel tank
3 Valve support
4 Diaphragm
5 Pressure spring
6 Connection to intake manifold
7 Valve
1
Fig. 12.25 Cross-section of the fuel-pressure regulator
450 The Motor Vehicle
can become contaminated when it is cold and when the engine is idling.
Therefore, to cleanse it and avoid subsequent inaccuracy of the signals output,
the wire is automatically heated to a high temperature for one minute every
time the engine is switched off.
12.17 Bosch Motronic system
Given that a microcomputer is used for regulating fuel injection, it can be
even more cost-effective to employ it for other control functions too. Primarily
the Bosch Mono-Jetronic system integrates injection and ignition controls,
but it can also be adapted for controlling other parameters such as exhaust
gas recirculation and evaporative emission canister purging, which are explained
in Sections 14.16 and 14.17. Comprehensive information on the electronic
components of the Motronic and other injection systems is given in the
Bosch publication Automotive Electric/Electronic Systems, and in their yellow
book entitled Motronic Engine Management.
Its intermittent injection system is basically identical to that of the L-

Jetronic, but all its signal-processing functions are done digitally. Among the
advantages of digital systems is that all the data processing can be done
directly by the computer, and much of the electronics can be common to a
wide range of applications. Also, operating data can be stored on maps,
which can be updated automatically by the computer to take into account
changes such as might occur as a result of, for example, wear of the engine
in service.
12.18 The electronic ignition control
Control of the ignition system is based on a spark advance characteristic map
stored in the memory of the Motronic control unit. The spark advance is
continuously changed to correspond to the setting on the map, taking into
account throttle position, and engine-coolant and air-intake temperatures.
When a spark is required, the electronic controller momentarily opens the
circuit to earth, whereupon the collapse of the field around the primary
generates the spark voltage in the secondary coil. The resultant high-voltage
current is passed through the distributor to the sparking plug. Generally,
there is neither a mechanical contact breaker nor a centrifugal and pneumatic
advance and retard system, though some high-speed six-cylinder engines
retain the centrifugal mechanism.
Obviously, a conventional mechanically actuated system could not vary
the ignition advance to satisfy the complex requirements that are registered
on the map, Fig. 12.26, and stored in the memory of the ECU. To obtain the
data points on the map, the engine is run on a dynamometer, the ignition
advance being optimised in respect of fuel consumption, emissions and
driveability. The data thus obtained are recorded electronically and transferred
into the memory of the ECU. By virtue of digital recording, the ignition
point for each condition of operation can be set independently of all the
others.
In operation, the microcomputer first reads from the map the point at
which, on the basis of the instantaneous engine speed and load, the next

spark should be triggered and then modifies it in relation to throttle position
and coolant and air temperatures. An inductive engine speed sensor signals
451Petrol injection systems
directly from the crankshaft. This is more precise than using a Hall-effect
sender in the distributor. Consequently, the spark advance can be optimised
while avoiding all risk of detonation, and both fuel utilisation and torque are
therefore improved.
Actually, there are two inductive pulse senders on the flywheel. One
senses the passage of teeth past its permanent magnet core, for translation
into engine speed. The other, for indicating crank angle, senses the passage
of either a pin or hole in the flywheel. These two signals are processed in the
control unit to make them compatible with the computer.
The parameters on the basis of which the ignition points are set include
fuel consumption, torque, exhaust emissions, tendency to knock and driveability,
the weighting given to each differing according to the type of operation. For
example, for idling, the priorities are low emissions, smoothness and fuel
economy; for part-load operation, they are driveability and economy; and for
full-load they are maximum torque and absence of detonation.
Ignition
advance
Rev/min
(a)
Load
Ignition
advance
Load
Rev/min
(b)
Fig. 12.26 At (a) is a three-dimensional map showing the degree of accuracy with
which the ignition timing can be controlled electronically as compared with, at (b), the

best that can be obtained with a mechanical and vacuum advance and retard
mechanism
452 The Motor Vehicle
For all types of operation other than part-throttle light load, correction
factors are applied to the map values. Also included in the control unit is a
switch which is actuated automatically during operation in the high-load
range, to cater for different fuels and grades of fuels. For starting, there is
even a correction routine for adjusting spark timing in relation to cranking
speed.
After the generation of each spark, a finite time is required for the re-
establishment of the current in the coil to its nominal value, ready for the
next firing. The higher the engine speed, and therefore frequency of sparking,
the longer is the dwell time needed to allow the current to build up in the
coil. Consequently, the relationship between current flow time in the coil and
supply voltage has to be regulated, by reference to a dwell angle characteristic
map similar to that in Fig. 12.27. As soon as the current has risen to the
appropriate level ready for the next ignition point, it is held there by the
output stage so that, as the dwell time shortens during acceleration from low
engine speeds, the appropriate current can be maintained throughout.
An indication of how the electronic control unit regulates injection and
ignition simultaneously can be gleaned from Fig. 12.28. To keep the break-
away and release times of the injection valves as short as possible without
using current-limiting resistors, the current to them is limited by a special
integrated circuit in the electronic control unit. For a six-cylinder engine, for
instance, the valve opening current is 7.5 amp and, at the end of the injection
period reduced to a holding current of 3.5 amp.
12.19 Fuel supply
As can be seen from Fig. 12.29, a roller-cell type pump delivers fuel, at a
pressure of 2.5 to 3 bar, through a filter removing particles down to 10
µ

m,
directly to one end of a fuel rail. At the other end is the pressure regulator,
Fig. 12.30, from which the return flow to the tank passes through a pulsation
damper, Fig. 12.31, to the tank. This, by reducing fluctuations in the pressure
in the return line, suppresses noises arising from both the operation of the
pressure regulator and the injector valves.
Dwell
angle
Rev/min
Battery voltage
Fig. 12.27 Three-dimensional plot showing how the dwell angle has to be varied
relative to the supply voltage and engine speed, to allow the current enough time to
build up in the primary winding
453Petrol injection systems
By virture of its large volume relative to the quantities of fuel injected per
cycle, the fuel rail acts as a hydraulic accumulator and ensures that all the injectors
connected to it are equally supplied with fuel. Injection occurs once per
revolution (twice per cycle) and is directed into the ports.
12.20 Overall principle of operation
A swinging-gate-type air flow sensor, described in Section 12.9, is employed
in the Motronic system, Figs 12.12 and 12.29. The duration of injection
required for maintaining the
λ
value at 0.85 to 0.95, as needed for engines
equipped with three-way catalytic converters, is assessed per piston stroke
and in relation to engine speed, instead of per unit of time. Corrections are
applied, as required, in response to signals received from detonation,
temperature, time and other sensors, and in accordance with plotted values
on engine performance maps. The sensors are as previously described for the
(a)

(b)
(c)
(d)
(e)
(f)
(g)
0° 120° 240° 360°
Fig. 12.28 Stages in the production of ignition sparks for a six-cylinder engine, by
means of an electronic control such as that in the Bosch Motronic system. (a) The
reference signal for the crankshaft angle; (b) an indication of the degrees of rotation
following the occurrence of the pulse signal; (c) the saw-tooth-shaped signal of the
angle counter; (d) characteristic of the instantaneous operating condition, as calculated
from the ignition and dwell angle signals and entered in the intermediate memory;
(e) when the values of the signals from the counter and the intermediate memory are
identical, signals are sent to the ignition output stage to switch the ignition coil on or
off; (f) low-tension signal for ignition; (g) current through the coil
454 The Motor Vehicle
Electric fuel pump
Fuel filter
Pressure
regulator
Ignition coil
High-tension
distributor
Injector
+
Air flow meter
λ
-sensor
Temp.

sensor
Throttle
position
switch
Idle speed
actuator
Inductive sensor
Sensor
wheel
Electronic
control unit
Fig. 12.29 Diagram issued by Bosch to represent their Motronic system for a four-
cylinder engine, which has a swinging-gate-type air flow sensor
Fuel inlet
Fuel outlet
Manifold
pressure
L- and LH-Jetronic systems, as also are the principles of operation of the
ancillary devices such as those for regulating air flow through the throttle by-
pass. Consequently, it is unnecessary now to present the features other than
in the form of a table and footnotes, Table 12.1.
12.21 Other variables
Intake air temperature. A sensor positioned in the air intake, Fig. 12.12,
Fig. 12.30 A Bosch diagrammatic
representation of the pressure regulator
for their Motronic injection and ignition
control system
455Petrol injection systems
Table 12.1—ADJUSTMENTS FOR VARIOUS OPERATING CONDITIONS
The following symbols are used to indicate the various sensors: TTS, thermal time switch; TVS,

throttle valve switch; ET, AT and K, engine and air temperature and knock sensors respectively.
Since all control functions call for signals from the air flow, intake temperature and engine speed
sensors (reflecting load), these are omitted to avoid repetition.
Operational Fuel Additional Ignition Additional Relevant
variables supply sensors timing sensors notes
Cold start Enriched TTS, TVS Retarded TTS, ET 1, 2, 3
Post start Enriched TTS, ET Advanced TTS 4
Warm-up Enriched ET Advanced ET 5, 6
Hot idling Normal ET Normal ET 7, 8
Full load Enriched TVS, ET Controlled ET, AT, K 9
Acceleration Enriched TVS, ET Controlled TVS, ET, K 10
Overrun Cut-off TVS Retarded TVS 11
(1) Cold start. Extra fuel delivered either by increasing the duration of opening of the injection valves, or
through the cold start valve (not shown in Fig. 12.29) which is in the manifold upstream of the injectors, or
both. For most engines, there is no need for a cold start valve; instead, the number of injections per revolution
may be increased and, since at very low speeds the quantity of air inducted is constant, the duration of the
injections is regulated on the basis of cranking speed, starting temperature and number of revolutions since
starting began. At higher cranking speeds throttling occurs, so the duration of injection is reduced.
(2) Rapid variations in speed during starting would lead to inaccurate air flow signals, so a fixed load
signal, weighted by engine temperature, is utilised by the control unit.
(3) The lower the cranking speeds and the higher the engine temperature the further must the timing be
retarded. In a cold engine, timing earlier than 10° BTDC can induce reverse torques, damaging the starter. On
the other hand, if the spark is retarded too much with high compression engines, knocking can occur at high
intake temperatures. At high cranking speeds, starting is improved if the ignition is advanced.
(4) Engine firing. At low temperatures and fast idle speeds, the ignition is advanced to improve both
performance and fuel economy. After a short time, it is progressively reduced to normal as the engine
temperature rises.
(5) Warm-up. Both enrichment and spark advance are progressively reduced as engine temperature rises
but, if a cold start valve is incorporated, its cut-off point must be compensated for, by increasing the flow
through the injectors. To improve driveability, the spark is further advanced during part load operation. In

general, after start-up, the ignition timing is adjusted (on the basis of engine temperature) for idling, overrun,
part and full load.
(6) To overcome oil drag, either an auxiliary air device or a thermostatically controlled rotary actuator,
Fig. 12.32, by-passes the throttle, and the electronic control supplies the extra fuel needed to maintain the
appropriate air : fuel ratio. This control operates on the basis of not only engine temperature but also speed,
load and an additional map similar to Fig. 12.33. For lean-burn engines, this is especially important since, in
situations in which driveability and good throttle response are critical, extra enrichment can be applied and,
in others, the fuelling reduced.
(7) Hot idling. By virtue of the application of the Motronic ignition control, enrichment is unnecessary
except during overrun when, if no overrun fuel cut-off is incorporated, a slight degree of speed-related
enrichment can improve driveability and reduce emissions.
(8) Ideally, the ignition timings for starting and idling should be different. By virtue of electronic control,
the spark can be advanced as speed is reduced, to increase torque during idling: consequently, the idling speed
does not have to be set to cater for the highest loads from the ancillaries, so both fuel consumption and
emissions are reduced.
(9) Full load. With Motronic, the degree of enrichment is related to the engine speed, but modified by the
map in the memory to cater for pulsations in flow and avoidance of knock. Maximum torque is obtained with
λ
= 0.9 to 0.95. The ignition point is set on the basis of the map but, to obtain maximum torque without knock,
modified in response to signals from the knock sensor. Thus high power output is obtained with good fuel
economy.
(10) Acceleration. The degree of initial enrichment is based on the signal from the throttle valve switch
and lambda sensor, the electronic control calling for a mixture at
λ
= 0.9, for maximum torque and avoidance
of a flat spot. For acceleration during warm-up, further enrichment is applied in response to engine temperature
signals. Ignition timing is adjusted in response to engine load and speed signals and, if a preset rate of change
of load is exceeded, the ignition timing is slightly retarded, to avoid knocking and generation of NO
x
.

(11) Overrun. After an initial lag, the ignition is first retarded (for a smooth transition) and then, a few
cycles later, the fuel is cut off completely. It cuts in again, over a few cycles, at an engine speed slightly higher
than idling and, once more, the ignition is first retarded and then, as the fuel begins to flow again, progressively
advanced back to normal. All this happens during stop–start situations in city traffic and normal braking and
down-hill operation, thus saving fuel and reducing emissions.
456 The Motor Vehicle
Mounting
Fuel
Fuel
Adjustment
screw
Diaphragm
Fig. 12.31 Bosch pulsation damper
for the Motronic system
signals to the electronic control unit which, at low temperatures, reduces the
fuelling to compensate for the low density, or mass, of charge and, at high
temperatures, reduces ignition advance to avoid detonation, especially for
turbo-charged engines, in which the higher temperature may not be offset by
a lower density of charge.
High altitude. A sensor signalling the reduction in pressure with altitude
can be incorporated in the electronic control unit, for reduction of the rate of
fuelling with increasing altitude.
Battery voltage. Battery voltage falls off with not only rapidly increasing
load but also decreasing temperature and age. Self-induction causes a lag in
both the opening and closing of the electro-magnetic injection valves.
Breakaway time depends to a significant degree on battery voltage, though
little on release time. Therefore, a fall in battery voltage causes a decrease in
injection time.
Fuel quality. To cater for premium and low grade fuel, some Motronic
electronic control units contain two maps for ignition advance relative to

load and speed, and the driver can switch from one to the other. Generally,
the program retards the ignition only at high loads.
Speed limiting. As in the L-Jetronic system, if required, injection can be
inhibited to limit maximum engine speed, the device cuts in and out respectively
at speeds of 80 rev/min above and below the required limiting value.
Engine stopped. To obviate danger of fire after an accident, a power
transistor in the control unit controls an external relay in a manner such that
the pump can operate only if the circuit between the starter and the battery
is closed or the engine speed is higher than a preset minimum relative to the
throttle position. Furthermore, to prevent the coil from overheating if the
engine is left switched on after it has been stopped or stalled, the microcomputer
turns off the ignition if the speed is less than, say, 30 rev/min.
Stop–start. To save fuel in heavy traffic, an additional controller can be
installed to signal either stop or start to the electronic control unit. To stop
the engine, the driver depresses the clutch pedal, and to start it again, he
depresses both the clutch and accelerator pedals simultaneously. However,
the engine will stop only if the speed is less than 2 km/h and start only when
the throttle is less than one-third open. A function of the additional controller
is to assess whether, in the light of the fact that each start uses extra fuel,
economy is in fact obtainable: if it is not, the engine will not stop.
457Petrol injection systems
Fig. 12.32 When the engine is idling, the Bosch Motronic control system sends
signals for this actuator to open a rotary valve to allow extra air to by-pass the throttle
and, at the same time, it increases the rate of fuel supply to maintain the appropriate
air : fuel ratio needed to cater for low temperature or the switching on of air
conditioning or other ancillary loads
Adjustable stop
Rotary valve
Electrical
connection

Return spring
Winding
Rotary armature
Warm-up
correction
factors
Rev/min
Load
Fig. 12.33 This map is an approximate representation of the correction factors needed
for increasing the rate of fuel supply needed, as indicated by the engine temperature,
when the engine is cold
Computer-aided transmission control. Fuel economy, gear shift quality,
and transmission torque capacity and life expectancy can be improved by
adapting the Motronic electronic control unit for use also in automatic
transmission control. Additional signals are needed by the unit, for controlling
the transmission’s hydraulic pressure regulator, its solenoid valves and
malfunction warning, include transmission output speed, kick-down switch,
and program (economy or sporting performance, and manual shift). Gear
shift performance curves in an electronic memory are much more effective
than their hydraulic counterparts for controlling gear changing. Furthermore,
458 The Motor Vehicle
the torque of the engine can be regulated during shifts, by momentarily
retarding the ignition during a shift, to obtain a part-load feel with a full-load
shift.
Exhaust gas recirculation. Exhaust gas recirculation can adversely affect
driveability, especially at low speeds and light loads. By employing the
electronic control unit for regulation of exhaust gas recirculation (EGR) in
relation to the engine performance map, these difficulties can be overcome.
The electronic control unit, through the medium of a pneumatic valve, regulates
the quantity of exhaust gas recirculated so that NO

x
is reduced at high loads,
and good driveability retained at light loads and low speeds. Further information
on EGR is given in Section 14.20.
Evaporative emissions. Canister purge, as described in Section 14.17, can
also be controlled by the ECU.
Boost pressure control. With turbocharged engines, the onset of knock
can be delayed by either reduction of boost or retardation of the ignition.
However, reduction of boost reduces performance, and retardation of the
ignition can cause overheating of the turbocharge. On the other hand if, as
soon as knock is detected, both are effected simultaneously in an interrelated
manner by the electronic control unit, these drawbacks can be largely avoided.
This is done by first retarding the ignition and then, during the lag before the
boost falls, advancing it progressively to its optimum value.
Cylinder cut-out. Where, in the interests of economy, there is a requirement
for one or more cylinders to be cut out of operation, the Motronic electronic
control unit can do so by cutting the fuel supply to the cylinder or cylinders
and, as more power is required, restoring it either to one at a time or to
groups of cylinders. Moreover, it can control a valve to direct hot exhaust gas
through the inactive cylinders, to keep them at normal operating temperature,
and therefore with normal values of friction between their moving parts.
Another significant advantage is that the working cylinders operate with the
throttle opened wider, and there is no throttling of the idle cylinders.
12.22 The Weber electronic control system
The Weber multi-point injection system is in many respects similar to the
Bosch systems already described, but its electronic control is totally different
and also exercises control over the ignition timing. Injection timing is calculated
on the basis of the throttle position, absolute temperature and pressure of the
air in the induction manifold, the instantaneous speed of the engine and
rotational position of the crankshaft. All these inputs are taken into account

together with other data in the memory of the electronic control unit, including
an engine performance map and the variation of volumetric efficiency with
speed. Compensation is effected for variations in the voltage of the battery
output. A more detailed description can be found in Automotive Fuels and
Fuel Systems, Vol. 1, by T.K. Garrett, Wiley.
12.23 Bosch Mono-Jetronic system
The single injector of the Mono-Jetronic system, Fig. 12.34, like that of the
GM Rochester TBI system, Fig. 12.36, injects intermittently into the air
intake, just above the throttle valve. A rotary, virtually pulse-free, electric
pump in the fuel tank delivers at a pressure of 1 kN/m
2
through a fine filter
459Petrol injection systems
to the injector. By virtue of its low output pressure, this pump is both
light and very economical to manufacture, many of its components being of
plastics.
The spray pattern is such that two jets are delivered, Fig. 12.35, one into
each of the crescent-shaped gaps between the edges of the throttle valve and
its cylindrical housing. Fine atomisation ensures that, even with the throttle
wide open, the mixture distribution is homogeneous. Fuel in excess of
requirements is returned to the tank, the continuity of supply preventing
formation of vapour locks. Each injection is triggered synchronously by the
ignition system and is timed to continue for periods of from 1 ms upwards,
according to the quantity of fuel needed.
The input to the electronic controller includes signals of engine speed
(from the ignition distributor), throttle valve position, and engine air intake
temperatures. Stored in its memory is the information it needs for use, in
association with the input signals, for calculating the time the injector is
required to remain open for supplying the quantity of fuel appropriate for
efficient operation of the engine.

The controller is programmed to enrich the mixture for cold starting,
warm-up and acceleration. In response to signals from the various electric
circuits, the engine temperature and speed sensors, an electric motor adjusts
1 Electric fuel pump 8 Throttle valve actuator
2 Tank 9 Throttle valve potentiometer
3 Filter 10 Lambda sensor
4 Air temperature sensor 11 Engine temperature sensor
5 Single point injector 12 Ignition distributor
6 Pressure regulator 13 Battery
7 Electronic control unit 14 ignition and starter switch
Fig. 12.34 The diagram issued by Bosch to illustrate their Mono-Jetronic single-point
injection system
2
3
6
4
5
7
8
1
11
10
13
14
9
12
460 The Motor Vehicle
the position of the throttle stop to set the idle speed at an appropriately low
level, regardless of what loads are switched in or out. As a contribution to
fuel economy and reduction of emissions a fuel cut-off operates the idling

system in the overrun condition and, if required in any particular application,
at maximum engine speed. Compensation is effected for variations in the
voltage of the output from the battery.
12.24 The GM Multec single-point system
Many features of the GM Multec single- (or throttle body) and multi-point
injection systems are similar to those of the Bosch Mono-Motronic and
Motronic systems respectively. A single-barrel, single-point, or TBI, system
is illustrated in Fig. 12.36, though twin-barrel versions are also available if
required.
From the submerged twin-turbine-type pump, fuel is delivered at a pressure
of 0.83 bar and rates from 19 to 26 g/sec, through a 15 µm filter to the
Fuel return
Fuel supply
Coil
Electric
connection
Fig. 12.35 Bosch low-pressure injector with twin jets for injecting the spray into the
two crescent-shaped openings on each side of the throttle valve as it opens
461Petrol injection systems
throttle body unit. A water separator/fuel strainer is attached to the fuel pick-
up beneath the base of the pump.
Fuel injection rates are regulated by an electronic control module (ECM),
and a separate electronic ignition module (EIM) controls the spark timing.
Air flow is metered by a conventional throttle valve. Sensors signal to the
ECM the throttle position, and temperature and absolute pressure in the
manifold. These and the other sensors are shown in Fig. 12.36.
Illustrated diagrammatically in Fig. 12.37 is the throttle body unit. This is
mounted on a riser, which is water jacketed to help to vaporise the fuel and
prevent icing in cold and damp ambient conditions. A coolant-temperature
sensor is screwed into the base of this jacket.

The fuel passes from the inlet lower than the chamber housing the injector,
through a fine mesh screen and up to the pressure regulator at the top, so any
bubbles of vapour developing will rise and be returned, together with the fuel
in excess of engine requirements, to the tank. Metering the fuel injected is a
solenoid-actuated ball valve. This valve is closed by a coil spring. When it is
open, the constant pressure maintained by the regulator projects a conical
spray into the bore upstream of the throttle valve. Regulation of the total rate
of delivery of fuel through the valve can be effected by varying either the
period open or the frequency of fixed-duration pulses.
The diaphragm-type pressure regulator valve is opened, against the resistance
of a calibrated spring, by the pump delivery pressure. It reduces the injection
pressure to 0.76 bar. As previously indicated, its primary function is to
maintain a constant pressure across the metering jet. The maximum recirculation
rate is 27 g/s.
Enrichment for cold starting, warm-up, acceleration and maximum power
are effected by the ECM, as also is idling speed. When the throttle is closed
on to its stop, extra air by-passes it through a duct in which is a tapered pintle
Lambda
sensor
ECM
a
Diagnostic
socket
Ign.
switch
Battery
Catalytic
converter
Ignition
distrib.

Oil pres.
switch
g
h
Ignition coil
d
e
f
Pump
relay
Filter
Throttle
body unit
Manifold
pressure
sensor
Vehicle
speed
sensor
Warning lamp
(check engine)
Fuel pump
in tank
a Plug-in calibration software EPROM d Idle air control valve
b Fuel pressure regulator e Coolant temperature sensor
c Injector f Throttle position sensor
Fig. 12.36 The GM Rochester Multec single-point injection system
cb
462 The Motor Vehicle
type idle air control valve. This valve is actuated by a stepper motor controlled

by the ECM in response to signals from the engine-speed sensor.
12.25 The Multec multi-point system
In principle, the GM Multec multi-point system resembles the Bosch Motronic,
Sections 12.17 to 12.21. To avoid repetition, therefore, only a few brief
comments will be made here. It is a complete engine-management system,
Fig. 12.38, regulating EGR, ignition, fuelling, overrun cut-off, air flow control,
including during idling, and open, or closed-loop control over emissions.
However, the ECM, is served by signals from the throttle position indicator
and manifold pressure and temperature sensors, and meters the air flow on
the speed–density principle, so the rate of fuelling is regulated in relation to
the computed mass flow. On the other hand, mass flow air metering with a
hot wire anemometer is an optional alternative. Among the features of the
system are on-board diagnostics, back-up fuel and ignition circuits, and an
assembly line diagnostics link. Another option is either direct or distributor
ignition timing.
Direct ignition of course obviates the need for a distributor and separate
coil. It can provide 35 kV, though typically it produces a 1700
µ
s spark at 18
kV. For a four-cylinder engine, a dual tower, twin-spark, epoxy-filled coil is
used, the current of which is closed-loop controlled, and there is back-up
control over ignition timing.
The injectors are of GM design, with alternative ratings of 12 or 2 ohm at
3 bar, and flow rates ranging up to 15 g/s. They are a push fit in bosses on
an extruded aluminium fuel rail, where they are retained by spring clips and
sealed by O-rings. The fuel pump impeller is of the two-stage vane and roller
type: the vanes remove centrifugally any vapour bubbles present and prime
Diaphragm and
self seating valve
assembly

Injector
electrical
terminals
‘O’ ring
(large)
Back-up
washer
Fuel
injector
Injector
fuel
filter
‘O’ ring
(small)
Nozzle
Regulator screw
(Factory adjusted)
Dust seal
Fuel inlet
(from fuel
pump)
Fuel
return
(to fuel
tank)
Regulator
spring
Fuel pressure
regulator
assembly

Fig. 12.37 The GM Rochester Multec single-point injector is similar to that of the
Bosch Mono-Jetronic
463Petrol injection systems
the roller-type pump of the second stage. A pulsation damper is mounted on
top and a fuel strainer/water separator sleeve is fitted to the inlet in the base
of the pump. At 3.5 bar, a delivery rate of 19 g/s is typical.
The oil pressures switch that can be seen in Fig. 12.38 controls a parallel
circuit to drive the fuel pump in the event of failure of either the pump relay
or the electronic control. Rated at 1000°C exhaust temperature, the oxygen
sensor has a zirconium element. Signals from the vehicle speed sensor indicate
to the ECM when overrun cut-off and idle-speed control should be brought
into operation.
Incorporated in the ECM are an 8-bit microprocessor, a co-processor, AC/
DC converters to enable the digital microprocessor to read the analogue
signals from the sensors, and the drivers for the actuators and back-up hardware.
Software and calibration are programmed into a 16-kbyte EPROM customised
to meet the requirements for specific applications. The co-processor relieves
the microprocessor of interruption by the engine timing functions.
Software alogarithms continuously check the status of the ECM outputs
and the validity of its inputs. If a fault is detected, a code is stored in the
memory and a warning lamp on the instrument panel illuminated. Service
technicians can then read the code indicating the nature of the problem and,
if necessary, connect to the system a diagnostic facility to obtain further
details.
12.26 Rover throttle body injection and ignition control
As previously indicated, single-point throttle body injection offers significant
cost economies as compared with multi-point injection. For this reason,
Rover retained it in the early 1990s for the models in the lower end of its
Manifold air temperature sensor
Pulsator

Fuel rail
Plug-in software and calibration EPROM
Throttle
position
sensor
Idle air
control
valve
Pump
relay
Warning
lamp
(check
engine)
Fuel
pump in
swirl pot
Vehicle
speed
sensor
Injector
Direct
ignition
unit
Oil pres.
switch
Crankshaft
sensor
Filter
Diagnostic

socket
ECM
Battery
Lambda
sensor
Manifold
pressure
sensor
Fig. 12.38 GM Rochester Multec multi-point injection system
~
Catalytic
converter
Ign.
switch
464 The Motor Vehicle
Fig. 12.39 The single-point version of the Rover modular engine-management system
(MEMS) that has been applied for injection on, among other vehicles in their range,
the Mini Cooper
General Description: The Single Point Injection system consists of a number of
components accurately maintaining the precise fuelling and ignition requirements.
Elecronic sensors monitor operation of the engine ensuring optimum performance
and economy under all running conditions.
Throttle Switch: Initiates the ECU to
provide idle speed and fuel cut off
when decelerating.
Ambient Air Sensor:
Monitors air temperature to
provide extra fuel enrichment
for cold starting.
Inlet Air Sensor: Detects

inlet manifold air
temperature enabling
accurate air/fuel ratio
during running
conditions.
Coolant Temperature
Sensor: Monitors engine
temperature, enabling ECU
to control engine speed
and fuel enrichment during
the warm-up period.
Knock Sensor: Provides
signals to theECU indicating
when detonation occurs and
in which cylinder.
Serial Diagnostic Connector:
Provides a communication link
using dedicated equipment to
enable system status to be
monitored and diagnosed.
Manifold Heater
Sensor: Switches
PTC manifold heater
during warm-up
conditions.
Inlet Manifold Absolute Pressure Sensor:
Situated in ECU and is connected by a pipe to
the inlet manifold. Detects engine load enabling
acccurate air/fuel ratio and ignition timing.
BH1431/Motor vehicle/ × 65%

Stepper Motor:
Maintains stable idle
under varying load
conditions regardless of
engine temperature
Crankshaft Sensor: Provides
engine speed and position
signals, enabling the ECU to
calculate injection and ignition
timing pulses.
465Petrol injection systems
Injector: Provides accurately
timed ‘pulses’ of fuel ensuring
correct mixture under all
running conditions.
Throttle Angle Potentiometer:
Senses throttle position and
speed of throttle movement.
PTC Manifold Heater:
Assists vaporisation of fuel
during warm-up conditions.
Electronic Control Unit
(ECU): Is a combined fuel management and
programmed ignition module. Computes signals
from sensors to provide: fuel injection pulse
timing and duration, ignition pulse timing and
engine idle speed.
Main Relay: Controls
electrical supply to the
ECU.

Fuel Pump Relay:
Controls electrical supply
to the fuel pump.
PTC Heater Relay:
Controls electrical supply
to the manifold heater.
Inertia Switch: Isolates
electrical supply to the
fuel pump and injector
under sudden vehicle
impact.
Fuel Pump: Delivers
fuel under pressure to
the injector.
Oil Pressure Switch:
Ensures fuel pump
does not operate when
there is a lack of oil
pressure.
System diagnosis is accessed initially via a serial diagnostic connector, which is also used
for electronically setting CO levels.
466 The Motor Vehicle
range, to satisfy the US Federal regulations until at least 1996. At the same
time, the old A-Series engine in the Mini Cooper was similarly equipped,
mainly for satisfying the Japanese emissions regulations. Interestingly, because
of the reduced breathing capacity of the manifold when TBI is substituted
for either twin-barrel or twin carburettors, there is almost invariably a slight
loss of power.
For their TBI system for the 1.4-litre engine, Rover use a Bosch injector
with solenoid actuated valve, Fig. 12.39. It is installed in a throttle body unit

designed by Rover and produced by Hobourn-SU Automotive, and the whole
assembly is mounted on the riser of a manifold that is also designed by
Rover. Bosch offer injectors with either ball- or pintle-type nozzles, but
Rover use the pintle type because experience has shown it to be more durable.
Rover design their own electronic hardware and software for injection-
control and engine-management systems, specifically to match their engines.
An indication of the success of this policy is that, while the European average
power output per litre for 1.3- to 1.6-litre engines with TBI at that time was
56 bhp/litre, the Rover 1.4 litre developed 68 bhp/litre. Incidentally, the
corresponding average for multi-point injection was 72 bhp/litre.
The single-point Modular Engine Management System (MEMS), Fig.
12.40, is a second-generation system, succeeding Rover’s earlier electronically
regulated ignition and carburation control (ERIC). Manufacture is undertaken
by Motorola AIEG, who have specialist production facilities.
An ignition timing map is programmed into the memory of the electronic
control unit (ECU), which regulates both the ignition and fuel metering.
Short circuit protection is incorporated, and powerful diagnostic facilites store
intermittent fault data. Either the Rover Microcheck or Cobest hand-held
diagnostic units can be plugged into a separate connector, without disturbing
the ECUs main connector. The ECU also controls both an electric heater at
the base of the manifold riser and a stepper motor for regulating idle speed.
12.27 Ignition control
Signals required by the ECU for ignition control include crankshaft angle
and engine speed (both from the crankshaft sensor), engine coolant temperature
and throttle closure, the latter indicated by the throttle switch. Additionally,
the manifold absolute pressure sensor converts the pressure to an electrical
signal to indicate engine load. To prevent fuel from entering the pressure
sensor, a vapour trap is inserted into the pipeline between it and the manifold.
The crankshaft sensor comprises an armature projecting into an annular
slot near the periphery of a reluctor disc bolted and spigoted to the flywheel.

Spaced 10° apart in the slot are 34 poles, which continuously update the
ECU as regards the crankshaft angle and engine speed. The two missing
poles, 180° apart, identify the TDC positions.
Basic ignition timing requirements are stored, as a two-dimensional map,
in the memory of the ECU, and various adjustments are signalled by the
sensors. For example, when the throttle and, with it, the switch contacts are
closed, an idle ignition setting is implemented and is further modified by
signals from the engine-temperature sensor. This system is so sensitive that
the idle ignition timing is continually varying.
The ignition coil has a low primary winding resistance (0.71 to 0.81 ohm
at 20°C), so that the high tension voltage will peak both rapidly and consistently
467Petrol injection systems
throughout the engine-speed range. Since the ignition timing is controlled by
the ECU, a simple distributor rotor and cap is used, the rotor being bolted to
the D-section rear end of the inlet camshaft.
12.28 The air-intake system
As can be seen from Fig. 12.41, the air is drawn first over a resonator, which
reduces noise output, Section 13.20, then through an intake temperature
Fuel
pump
WP
B
Distributor
cap
Inertia
switch
Ign
coil
WB
NX

P.T.C.
heater
KS
NK
NK
NK NU GK GW
N
NN
N
Main
relay
P.T.C.
relay
Fuel
pump
relay
Injector
NK
Throttle
potentiometer
KB
Throttle
body
Stepper
motor
Air-conv.
active
Diagnostic
socket
YG YP

KB
WB WK BG BP NK YN OS OU KUOG UB WY BG
25 4 6 20 28 24 3 27 2 22 19 10 15
11 14 29 13 31 32 30 33 16 35
GW B B KS UPWU KB KG GB UR
8
9
N
GK
Ign
switch
N
Throttle
switch
KB
B
+ –
Battery
Crankshaft
sensor
Manifold
absolute
pressure
Coolant
sensor
KB
Inlet
air
sensor
KB

Air-conv.
sensor
Inputs from (sensors, etc.): Outputs to:
Crankshaft angle Diagnostic unit Injector
Ignition coil Power earth Stepper motor
Manifold absolute pressure Sensor earth Fuel pump relay
Coolant temperature Air-to-converter request Manifold heater relay
Inlet air temperature Ignition supply Main relay
Throttle potentiometer Battery supply Diagnostic output
Throttle pedal position (switch) Air-to-converter clutch
Fig. 12.40 Diagrammatic representation of the Rover electronic control system
468 The Motor Vehicle
control valve, and on past the air intake temperature sensor to the filter
mounted on the combined throttle body and injector housing. The air
temperature control valve is a hinged flap over the end of a duct taking
heated air (from a shroud around the exhaust manifold) to mix with the
incoming cold air. The flap, moved by a diaphragm-type actuator controlled
by a Thermac valve, is closed by a return spring and opened by manifold
depression.
When the engine is started in an ambient temperature below 35°C, the
flap is immediately opened by manifold depression, to allow warm air to
pass into the induction system. As the engine warms up and the temperature
of the incoming air rises above 35°C, the Thermac valve opens, to vent the
depression to the clean side of the air filter. A restrictor in the connection
from the manifold to the Thermac valve serves two purposes: first, it damps
the motion of the valve so that it does not snap closed and open, but hovers
between the two positions, holding the temperature of the air delivered to the
cleaner at around 35°C; secondly, it ensures that opening the Thermac valve
has a negligible effect on the manifold depression.
From Fig. 12.41, it can be seen also that a hose is connected between a

fuel trap incorporated on the left of the air filter and the ECU, and there is a
second hose between the fuel trap and a point downstream of the throttle.
Thus, absolute pressure in the manifold is transmitted to the ECU, in which
is a pressure sensor. Incidentally, there is also a throttle by-pass passage, but
this is not shown in the illustration. At low engine speeds, fine adjustment to
the air flow, and therefore mixture strength, can be made by means of a
screw projecting into this passage.
13
14
1
12
11
6
7
8
3
2
4
10
5
1 ECU pipe 8 Hot air intake
2 Vapour trap 9 Resonator
3 Thermac valve 10 Inlet air sensor
4 Air filter 11 Breather pipe
5 Temperature control diaphragm 12 Breather pipe (restricted)
6 Temperature control flap 13 Thermac valve (manifold)
7 Cold air intake duct 14 Thermac valve (diaphragm)
Fig. 12.41 Schematic representation of the Rover single-point injection system
9