Automotive mechanics (volume II)(Part 2, chapter13) electronic fuel injection and engine management

217-250_May 2chap 13

13/9/06

3:48 PM

Page 217

217

Chapter 13

Electronic fuel injection
and engine management

Basic principles of EFI

Testing equipment

Types of EFI systems

Technical terms

Block diagrams of an EFI system

Review questions

Operation of a multipoint EFI system
Components of an EFI system
Engine management
Electronic concentrated control system

Sequential multipoint fuel injection system
Other features of engine control systems
Throttle-body injection (TBI)
Servicing engine control systems
Locating basic faults
Fault diagnosis


217-250_May 2chap 13

13/9/06

3:48 PM

Page 218

218 part two fuel and engine management
Electronic fuel injection (EFI) is a fuel system for
petrol engines which uses electronically controlled
injectors to spray fuel into the engine’s intake manifold. The system has an electronic control unit (ECU),
or computer, to control injection. The ECU receives
input signals from various sensors, which it processes.
It then sends output signals which adjust the quantity
of fuel being injected and, in some cases, when the fuel
is injected.
The computer can be arranged to monitor almost all
engine controls. This monitoring and controlling
process is usually referred to as engine management.
The control units of different manufacturers are called
by many different names but the generic term ECU

(electronic control unit) will be used in this chapter.
Engine management systems use electronics to
not only control fuel injection, but they also control
ignition and emissions for improved engine
performance.

Basic principles of EFI
The basic operation of an EFI system hinges around
two main components:
1. Electrically operated injectors, which spray fuel
into the intake manifold (Figure 13.1).
2. An ECU (Figure 13.2), which collects information
from various parts of the engine and controls the
fuel delivered by the injectors.

figure 13.2

ECU and wiring harness

HOLDEN LTD

EFI compared with a carburettor system
Apart from the petrol tank, almost all the components
of an EFI fuel system are different from those of a
carburettor fuel system. EFI performs the same overall
functions as a carburettor, but there are a number of
reasons why EFI is used.
One of the main reasons is that the air–fuel ratio
can be closely controlled throughout the operating
range of the engine. This is much harder to do with a

carburettor, where various methods of mixture
correction have to be used.

Types of EFI systems
There are two main types of EFI. The difference
between the systems is the location of the injectors and
their mode of injection (Figure 13.3). These two
systems are as follows:
1. Multipoint injection. A separate injector is used for
each cylinder, and the fuel is sprayed into the intake
ports. This is also called port injection.
figure 13.1

Fuel injector located in the manifold at the
intake valve port FORD

The quantity of fuel delivered by the injectors is
quickly adjusted by the ECU to meet changes in
engine conditions. Almost instantaneous changes can
be made to the quantity of fuel being delivered to the
engine.

2. Throttle-body injection. One or two injectors are
used in a throttle body which is mounted on the
intake manifold in a similar manner to a carburettor. This is also called single-point injection.
Very simply, the throttle body and injector form an
electronically operated carburettor.
Both EFI systems use a similar type of electronic
control and their injectors operate in a similar way.
As well as these two systems, there are mechanical

injection systems and also systems that are both


217-250_May 2chap 13

13/9/06

3:48 PM

Page 219

chapter thirteen electronic fuel injection and engine management
air

219

Multipoint EFI system
plenum
chamber

special length
tubes

Figure 13.4 shows a basic multipoint EFI system. The
parts are:
1. Air cleaner and ducts to provide clean air.
2. Airflow meter to measure the flow of air.

injectors

injectors

3. Throttle valve, which controls the flow of air into
the engine.
4. Plenum chamber (surge tank or swirl chamber) to
dampen the flow of air.
5. Fuel tank to store fuel.

(a) Multipoint injection
injector
air

air

intake manifold

6. Electric fuel pump to provide pressure in the
system.
7. Fuel filter to protect the injectors.
8. Fuel rail to supply the injectors with fuel.
9. Injectors that spray fuel into the intake ports.
10. Pressure regulator to control the pressure in the
system.

(b) Throttle-body injection

figure 13.3

Diagrams show the difference between
multipoint and throttle-body injection

11. ECU to control injection and other engine
requirements.
Throttle-body injection

mechanical and electronic. EFI systems are the most
commonly used; other systems will not be covered here.
■ Throttle body injection is sometimes called centrepoint or central injection.

Figure 13.5 is a basic throttle-body, or single-point,
EFI system. This has the same type of supply system
as a multipoint system, but it has a throttle body with
an injector. In both systems, the ECU is used to control
the quantity of fuel delivered by the injectors.
electronic
control unit (ECU)

figure 13.4

Basic multipoint EFI system


217-250_May 2chap 13

13/9/06

3:48 PM

Page 220

220 part two fuel and engine management

electronic
control unit (ECU)

figure 13.5

Basic throttle-body injection (TBI) system

EFI subsystems
An EFI system has three subsystems:
1. an air-intake system
2. a fuel system
3. a control system.
These provide the mixture of air and fuel, and control a
number of other functions. The basic EFI systems
(Figures 13.4 and 13.5) have these three subsystems,
and the parts of each can be identified on the simple
diagrams.
All EFI systems, whether simple or complex, will
have the three subsystems. This is the way in which a
system should be looked at, as it is easier to understand
if the subsystems are examined separately.

Block diagrams of an EFI system
An easy way to identify the components of an EFI
system is by using block diagrams. Figures 13.6 to
13.9 show block diagrams for the air, fuel and control
subsystems of a multipoint system.

2. Airflow sensor. This measures the quantity of air
flowing into the system so that the correct amount
of fuel can be provided for the optimum air–fuel
ratio.
3. Throttle body. The throttle body has a throttle valve
that is operated by the accelerator pedal. This
controls the amount of air that enters the engine.
4. Plenum chamber. This acts as a surge tank and
distributes the air to the branches of the intake
manifold.
5. Intake manifold. The branches or pipes of the
manifold carry air to the cylinders and also provide
a mounting for the injectors.
air

air
cleaner

airflow
sensor

throttle
body

engine

intake
manifold

plenum

chamber

figure 13.6

Air-intake system
In the block diagram of an air system shown in Figure
13.6, the air enters at the air cleaner and flows through
the system to the engine.
The parts and their functions are as follows:
1. Air cleaner. This has a cellulose fibre element
which provides clean air for the system.

Block diagram of the air system for
multipoint EFI

Fuel system
The main parts of a return-to-tank fuel system are
shown in the block diagram in Figure 13.7.
1. Fuel tank. This performs the normal function of
holding fuel. It has a fuel supply line and a return


217-250_May 2chap 13

13/9/06

3:48 PM

Page 221

chapter thirteen electronic fuel injection and engine management

221

fuel tank
assembly

fuel filter

fuel
pump

figure 13.7

pressure
regulator

Block diagram of a fuel system for multipoint
EFI (return-to-tank system)
engine

line. In some installations, a submerged fuel pump
is fitted.
2. Fuel pump. An electric pump is used. This has the
electric motor and pump in a common housing and
operates whenever the engine is running. If the fuel
pump is fitted above the level of the fuel tank, an
additional low-pressure pump is sometimes located
inside the fuel tank to prime the main pump.
3. Fuel filter. A paper filter is fitted in the fuel line so

that all the fuel is filtered before it reaches the
injectors.
4. Fuel rail. The fuel rail, or distributor pipe, receives
fuel from the filter and supplies it to the injectors.
All the injectors are connected in parallel with the
common fuel rail.
5. Injectors. These spray atomised fuel into the intake
ports of the engine. For each rotation of the crankshaft, each injector valve opens once, regardless of
whether the inlet valve is open or not.
If the valve is closed, the fuel is stored in and
around the inlet port until the next time the valve
opens. The fuel will then be drawn into the combustion chamber. With this arrangement, only half
the fuel requirements are injected each time
injection occurs.
6. Pressure regulator. The pressure regulator is fitted
at the end of the fuel rail. It maintains the pressure
in the system high enough for injection. The pressure regulator also maintains a constant pressure
differential across the injector.
■ This arrangement is referred to as a return-to-tank
system because it has a return fuel line from the
pressure regulator in the engine compartment.
Returnless fuel system
The main parts of a returnless fuel system are shown
in the block diagram in Figure 13.8. This system has

figure 13.8

injectors

fuel rail

Block diagram of a returnless fuel system for
multipoint EFI

been developed in order to overcome the evaporative
emission problems associated with returning hot fuel
from the fuel rail back to the fuel tank. The main
features that are different from a return-to-tank system
are:
1. Fuel tank. In this system the fuel tank also houses
the fuel pump, fuel filter, and pressure regulator
assembly. There is no return line from the fuel rail.
2. Fuel pump. The pump assembly contains the
fuel filter, the pressure regulator valve and the fuel
gauge sender unit (see Figure 13.33).
3. Fuel filter. The filter, as part of the pump assembly,
is mounted in the fuel tank.
4. Pressure regulator. The pressure regulator is part
of the pump assembly fitted inside the fuel tank as
shown in the diagram. It maintains the pressure in
the system high enough for injection.
Control system
The electronic control system consists of a central
ECU and a number of sensors and other electronic
controls. The sensors are shown in the block diagram
in Figure 13.9. By various means, these sense or
measure the conditions at their locations and this
information is transmitted to the ECU.
1. ECU. This is an electronic device that processes the
information provided by the sensors. It then allows

the injectors to pulse to earth, which determines
their opening period, and therefore the quantity of
fuel injected.
2. Timing sensor. An engine-driven sensor provides a
signal which, after being processed by the ECU, is
used to time the injectors. Each injector could be


217-250_May 2chap 13

13/9/06

3:48 PM

Page 222

222 part two fuel and engine management
timing

airflow

air
temperature
coolant
temperature
throttle
position

electronic
control unit

(ECU)

■ Some engines have a cylinder-head temperature
sensor instead of, or in addition to, the coolanttemperature sensor.

injectors

other

figure 13.9

7. Other sensors. Other sensing devices are used for
particular conditions, such as for cold starting.
The voltage of the electrical system is also taken
into account because the state of the vehicle’s
electrical system affects the operation of the
injector solenoids. Adjustment is made to
compensate for changes in voltage.

Block diagram of a control system for EFI

opened once per engine revolution, or once each
second engine revolution.
3. Airflow sensor. Already referred to as part of the air
system, the airflow sensor provides a continuous
measurement of all the air being taken into the
system. The ECU directs the injector to provide
the right amount of fuel to suit the air.
■ The relationship of the following should be noted:
the throttle valve, which is controlled by the driver

through the accelerator, determines the amount of
air flow; the airflow sensor measures the air flow;
and the injector provides an appropriate amount
of fuel.
4. Air-temperature sensor. This is installed in the
airflow meter or the intake air stream to measure
the temperature of the air being drawn into the
system. The density of air (and the amount of
oxygen the air contains) is related to its temperature. The ECU adjusts the quantity of fuel to
suit the air density.
5. Coolant-temperature sensor. This is a sensor in the
cylinder head that measures the coolant temperature. It enables a slightly richer mixture to be
provided when the engine is cold.
6. Throttle-valve switch. This is operated by the
throttle-valve shaft and is used to tell the ECU
when the engine is idling so that the mixture
strength can be slightly adjusted. The throttle
sensor is also used to indicate various positions of
throttle opening.

Operation of a multipoint
EFI system
Figure 13.10 shows the arrangement of a Bosch
L-Jetronic fuel system. This contains the three
subsystems (air-intake, fuel and control) which have
been previously described. The principles of the
L-Jetronic system have been applied to many other EFI
systems and it has been developed further to include
engine-management functions.
Bosch components, or components of similar

design, are used in many other systems. The operation
of the system will be described, and then the components will be considered in greater detail.
Air-intake system
The air system provides clean air to the engine and
also measures air flow. It operates as follows:
1. Filtered air from the air cleaner (not shown) passes
into the airflow sensor (12).
2. The airflow sensor measures the quantity of air as
it flows through. This information is sent to the
ECU (6).
3. The throttle valve (11) is used by the driver to
control the flow of air into the engine and so
control the engine’s speed and power. The position
of the throttle valve is relayed to the ECU by the
throttle-valve switch (10).
4. Air passes through the plenum chamber and then
into the intake manifold before entering the engine.
5. Air enters the engine through the intake valve and
is mixed with fuel sprayed from the injector (7) to
form a fuel charge.
6. The auxiliary-air device (18) allows extra air past
the throttle valve when the engine is cold to speed
up the engine. This has a similar effect to opening
the throttle slightly.


217-250_May 2chap 13

13/9/06

3:48 PM

Page 223

chapter thirteen electronic fuel injection and engine management

223

figure 13.10

Schematic arrangement of the L-Jetronic system
1 fuel tank, 2 electric fuel pump, 3 fuel filter, 4 fuel rail or distributor pipe, 5 pressure regulator, 6 ECU,
7 injector, 8 start valve, 9 idle-speed adjusting screw, 10 throttle-valve switch, 11 throttle valve, 12 airflow sensor, 13 relay,
14 lambda or oxygen sensor, 15 coolant-temperature sensor, 16 thermo time switch, 17 distributor, 18 auxiliary-air device,
19 idle-mixture adjusting screw, 20 battery, 21 ignition starter switch BOSCH

Fuel system
The fuel system pumps fuel from the fuel tank and
sprays it into the intake manifold through the injectors:
1. The fuel is pumped from the fuel tank by an electric
pump (2) which maintains a pressure in the system.
2. Fuel is filtered as it passes through the filter (3) into
the fuel rail or distributor pipe (4).
3. Fuel pressure is held in the fuel rail by the pressure
regulator (5).
4. The injectors are connected to the fuel rail. They
spray fuel into the intake manifold when directed
by the ECU.
5. A start valve (8) is used for cold conditions. This
supplies additional fuel for starting.

Control system
The control system receives input signals (information)
from a number of sources, processes them, and sends
out signals to the injectors.

When the ignition switch (21) is turned on, the
relay (13) is energised and the ECU (6) is activated.
The ECU can then adjust injection to suit the
information that it receives. This information comes
from a number of sensors:
1. the distributor (17) for engine speed and ignition
timing
2. the airflow sensor (12) for the quantity of air (for
which the right amount of fuel must be injected)
3. the throttle switch (10) for the throttle-valve
opening
4. the temperature sensor (15) for coolant temperature
5. the oxygen sensor (14) in the exhaust manifold, for
correct air–fuel mixture
6. the thermo time switch (16) for the length of time
that the cold-start valve remains operative.


217-250_May 2chap 13

13/9/06

3:48 PM

Page 224

224 part two fuel and engine management

Components of an EFI system
The above covers the general operation of a multipoint
EFI system. The components will now be considered
in more detail.
Airflow sensor
The airflow sensor in Figure 13.11 consists of a flap or
vane that is deflected by the flow of air through the
sensor. The flap is connected to the moving contact of a
potentiometer (variable resistance) so that the resistance
of the potentiometer is varied according to the position
of the flap. This provides a voltage signal that is related
to air flow. The ECU then adjusts the fuel from the
injectors to suit the amount of air entering the engine.
The flap is V-shaped. One part of the flap is used as
an airflow valve; the other part is a compensating flap.
This operates in a damping chamber to dampen flap
movement.

■ This is a basic method of sensing air flow. Other
sensors are covered later.
Air-temperature sensor
An air-temperature sensor is fitted in the intake side of
the airflow sensor. This measures the density of the
incoming air and signals this information to the ECU.
The ECU adjusts the fuel to suit air density.
Fuel pump
The fuel pump is a roller-cell electric pump (Figure

13.12). It consists of a pumping element and an
electric motor in a common housing. An electric pump
is used because the system must be full and pressurised
before the engine can be started. The injectors need
pressure to spray starting fuel into the intake manifold.
The pump has an inlet at one end and an outlet
at the other. Fuel flows straight through the pump,
and this both lubricates and cools the pump motor.
A permanent-magnet-type motor is used and this
drives the roller-cell pump element.
The roller-cell pump consists of a rotor in a housing
(Figure 13.13). Slots in the rotor carry the rollers. The
rotor is offset in its housing to form a pumping
chamber so that fuel is carried around between the
rollers as the pump rotates.
■ The fuel system must be pressurised before the
engine can be started.
Fuel filter
The filter is an in-line filter between the pump and the
regulator. It has a paper filter element as well as a
screen to trap larger particles (Figure 13.14).
Fuel pressure regulator

figure 13.11

Airflow sensor of the flap or vane type

FORD

The pressure regulator (Figure 13.15) is used to

maintain a regulated pressure in the system, at a
nominal 250 kPa. The regulator has a metal housing
with a spring-loaded diaphragm. When pressure builds
up, the diaphragm lifts the valve to return surplus fuel
back to the tank. The pressure is set during manufacture and is determined by the strength of the spring.
The chamber above the diaphragm is connected to
the intake manifold, and so subject to manifold
vacuum. Changes in manifold pressure will therefore
vary the pressure in the fuel system. However, with
this arrangement, the pressure difference across the
injector valves is held constant. With the pressure


217-250_May 2chap 13

13/9/06

3:48 PM

Page 225

chapter thirteen electronic fuel injection and engine management

figure 13.12

Roller-cell electric fuel pump assembly

figure 13.13

Roller-cell pump element

figure 13.14

Fuel filter for an EFI system

225

FORD

FORD

figure 13.15
BOSCH

constant, the quantity of fuel injected is related only to
the time that the injector is open.
■ This is a return-to-tank fuel system with the
pressure regulator at the end of the fuel rail.
Fuel injector
The location of the injector of a multipoint system was
shown in Figure 13.1. It is fitted in the intake manifold
so that the fuel is sprayed directly into the intake port

Fuel-pressure regulator for an EFI system
FORD

in the cylinder head. The fuel is directed in a finely
atomised form with a spray angle of about 25°.
The atomised fuel is maintained in suspension in
the air. Wetting the surfaces of the manifold and valve

port is avoided because this would leave unmixed fuel.
This fuel would not be fully burnt in the combustion
chamber and would contribute to hydrocarbon
emissions in the engine’s exhaust.
The injector is fitted into the manifold in special
rubber mouldings which protect it from heat and


217-250_May 2chap 13

13/9/06

3:48 PM

Page 226

226 part two fuel and engine management
vibration. It has an electrical connection and a fuel
connection.
A section through an injector is shown in Figure
13.16. Fuel is supplied through the top of the injector
and retained in the injector by the needle valve, which
is held on its seat by the spring. At appropriate times,
electrical pulses from the ECU energise the solenoid
windings and attract the plunger and needle away from
its seat. As a result, a spray of fuel is directed into the
intake port of the engine.
■ The needle has a very small lift. When fully open,
this is only about 0.1 mm.

As well as these, there are a number of compensating signals, such as engine temperature and air
temperature, for which the air–fuel mixture is modified
from that used for normal operation. The ECU
provides for a basic amount of fuel to be delivered by
the injectors, and this is then varied to suit the different
operating conditions.
The distributor is used to signal engine speed and
also the crank-angle position for injection timing. The
pulse signal is passed through a pulse-shaping circuit
in the ECU, which changes it from peaks into a
rectangular form (Figure 13.17). The pulse is then used
to operate the injectors.

figure 13.17

Pulse signal to the injectors – pulse width
can be varied, as shown by (a) and (b), for
different engine conditions

In the diagram, each rectangular pulse represents
the opening of an injector. The height represents
voltage, and the width represents time. The ECU
widens the pulse for higher loads and increases the
frequency of the pulse for higher engine speeds. At
low engine loads, the pulse is narrow, so only a small
quantity of fuel is delivered by the injectors.
Figure 13.18 shows the main inputs and outputs of
an EFI control system, while the diagram in Figure
13.19 illustrates how the ECU adjusts to suit different
operating conditions.

Engine-temperature sensor

figure 13.16

Section through a fuel injector for multipoint
EFI TOYOTA

Electronic control unit (ECU)
The ECU receives two main signals:
1. engine speed
2. the amount of air taken in by the engine.

A rich air–fuel ratio is needed for cold starting and for
warming up, so the ECU needs to know the engine temperature. This signal is supplied by the engine coolanttemperature sensor (Figure 13.20).
The temperature sensor is screwed into the engine
block or cylinder head with its end extending into the
water-jacket. The end of the sensor is a thermistor with a
negative temperature coefficient. The resistance of the
sensor decreases as its temperature increases. This change
in resistance is used to measure engine temperature.


217-250_May 2chap 13

13/9/06

3:48 PM

Page 227

chapter thirteen electronic fuel injection and engine management

figure 13.18

The main inputs and outputs of an EFI control system

227

BOSCH

down and
deceleration

figure 13.19

The ECU adjusts the basic amount of fuel injected to suit different engine-operating conditions

Cold-starting devices
The cold-start valve injector is operated by a solenoid.
It sprays fuel into the manifold for cold starting and is

operated by the cranking signal via the thermo-time
switch.
The thermo-time switch (Figure 13.21) is mounted


217-250_May 2chap 13

13/9/06

3:48 PM

Page 228

228 part two fuel and engine management
Idle-speed control
Idle-speed control is shown in Figure 13.22. The air
sensor has an adjusting screw which allows air through
the bypass in the air sensor. The air can be adjusted for
idling mixture.

figure 13.20

Engine coolant-temperature sensor
BOSCH

figure 13.22

Idle-speed control and airflow sensor

BOSCH

on the engine where it is affected by both engine
temperature and ambient air temperature. It is a
bimetal switch which has its contacts closed at lower
temperatures so that extra fuel is delivered by the start
valve. When hot, the switch contacts are opened to
switch off the start valve. The bimetal switch is also
electrically heated, so that the contacts automatically
open after a short period of time.

For cold idle, the auxiliary-air device allows some
air to bypass the throttle valve. This air has already
been measured by the air sensor and taken into account
by the ECU in determining the amount of fuel to be
injected. The bypass air therefore has the same effect
as opening the throttle valve.

■ The cold-start injector operates only during
cranking.

The throttle-valve (throttle-position) switch is operated
by the throttle. It has a set of contacts for both idle and
full-throttle positions (Figure 13.23). The switch
signals the throttle opening to the ECU, which provides mixture correction for both idle and full-throttle
conditions.

Throttle-valve switch

full-load
contacts
cam

throttlevalve shaft

idle contact

figure 13.21

Thermo-time switch for a cold-starting

device BOSCH

figure 13.23

Throttle-valve (throttle position) switch
BOSCH


217-250_May 2chap 13

13/9/06

3:48 PM

Page 229

chapter thirteen electronic fuel injection and engine management

229

Oxygen sensor

Engine-management system components

The oxygen sensor (Figure 13.24), also referred to as a
lambda sensor, is used to provide a closed-loop
system.

Figure 13.25 shows the input and output components
of one engine-management system, and their relationship with the ECU. Figure 13.25(a) illustrates the input

devices that generate input signals for the ECU.
Figure 13.25(b) illustrates the output devices that
receive signals from the ECU.
Many of the functions carried out by the ECU could
be performed in other ways, but electronic control has
been extended beyond injection and ignition. Components such as the air conditioner and turbocharger have
been included. For example, the air-conditioner
compressor can be stopped at idle so that the engine
idles better and produces less emission. The
turbocharger can be controlled and warning signals
provided.
Input devices

figure 13.24

Exhaust-oxygen (lambda) sensor

HOLDEN LTD

The oxygen sensor is located in the exhaust
manifold and is used to detect the oxygen content of
the exhaust gases as they pass from the engine. The
amount of oxygen in the exhaust is a measure of
the air–fuel ratio of the mixture entering the engine.
The oxygen sensor feeds information to the ECU,
which then adjusts the fuel from the injectors. This is a
continuous process, so the optimum air–fuel ratio is
always obtained.

Starting from the top of Figure 13.25(a) and moving

clockwise, the input devices and their functions are
described briefly as follows:
1. Air-conditioning switch. Signals that the air
conditioner is switched on.
2. Airflow meter. Measures air flow passing into the
engine.
3. Electrical switches. These include the headlamp
switch, blower switch and electric-fan switch.
They have an effect on engine load.
4. Power-steering pressure switch. Signals that the
power steering is functioning.

■ A closed-loop system provides feedback, whereas
an open-loop system has no feedback.

5. Throttle sensor. Senses throttle opening.

Engine management

7. Oxygen sensor. Measures the amount of oxygen in
the exhaust gases.

Systems with EFI, in which the ECU is used to control
injection, ignition and engine emissions, are referred to
as engine-management systems. Almost all the
functions associated with the engine can be controlled
electronically.
With any engine system, the fuel system and the
ignition system are the two most important items to
be controlled because they affect both engine performance and exhaust emissions. Data stored in the

memory of the ECU is compared with information that
it receives from the various switches and sensors.
Output signals then adjust the fuel and ignition to give
optimum engine performance.

6. Coolant thermosensor. Senses the coolant
temperature.

8. Air-intake sensor. Senses the temperature of the
incoming air.
9. Diagnosis connector. This is a multiterminal
connector to which diagnostic test equipment is
connected. It is used to check inputs to the ECU.
10. Neutral/clutch switch. Signals that the engine has
no load.
11. Stop light switch. Signals braking.
12. Ignition switch. Supplies power to the ECU and
signals starting.
13. Battery. This is the general power supply.


217-250_May 2chap 13

13/9/06

3:48 PM

Page 230

230 part two fuel and engine management

figure 13.25

Components of an engine management system
(a) ECU and input devices (b) ECU and output devices

FORD


217-250_May 2chap 13

13/9/06

3:48 PM

Page 231

chapter thirteen electronic fuel injection and engine management

14. Distributor. Provides engine-speed signals and
crank-angle signals.
15. Knock sensor and knock control unit. Detects
detonation and signals the need for less spark
advance.
Output devices
Figure 13.25(b) shows the output devices to which the
ECU sends signals. The system shown includes turbocharger devices. The functions of the output devices of
the system are briefly as follows:
1. Overboost warning buzzer. This is a warning
signal that the turbocharger pressure is too high.

2. Air-conditioning circuit relay. Opens at idle and
full throttle to stop the air-conditioning compressor and relieve the load on the engine.
3. Fuel injector. Sprays fuel as directed.
4. Diagnosis connector. Checks output signals with
test equipment.
5. Solenoid valve. This is used for fuel-pressure
regulator control.
6. Wastegate solenoid valve. Controls the turbocharger wastegate.
7. Solenoid valve. Used to purge the charcoal
canister (emission control).
8. Fuel pump resistor/relay. Reduces fuel pump
voltage and reduces pump speed when requirements are low.
9. Igniter. Used for ignition-timing control.
10. Air-conditioning relay. Switches the airconditioning compressor on and off.
11. ISC valve. This is the idle-speed control valve.
12. Turbocharge indicator. Lights to show that the
turbocharger is in operation.
■ Output devices are sometimes called actuators.
Different management systems
While engine-management systems generally perform
similar functions, there are many variations in arrangement and design. The L-Jetronic, as described earlier, has
engine-management variations such as the Motronic.
Some other systems have been given names, such as the
electronic concentrated control system (ECCS),
electronic engine control (EEC), electronic concentrated
injection (ECI), and central fuel injection (CFI).

231

The systems that are described in the following

sections are representative of those in use, but
reference will have to be made to the relevant service
manual for information on any particular system.

Electronic concentrated
control system
A diagram of an electronic concentrated control
system (ECCS) is shown in Figure 13.26. This is an
engine-management system. As with all systems, there
are four factors to be considered: air, fuel, ignition, and
control. The following are points relating to
components of the system.
Air system
Air from the air cleaner passes through the airflow
meter and then through ducting to the throttle body and
air chamber before entering the engine. A number of
auxiliary-air devices are used in conjunction with the
air chamber for cold starting and idle.
Airflow sensor
An airflow sensor is illustrated in Figure 13.27. In this
design, a heated wire in the sensor is located in the
path of the air flow and used as a sensing element. Air
passing over the heated element produces a cooling
effect, which reduces its temperature.
Changes in temperature are used as signals to the
ECU. The signals are used to measure the mass of air
flowing through the air sensor and into the engine.
Idle air supply
At engine idle, the throttle valve is closed and allows
very little air to pass, so idle air passages are provided

in the air system. These bypass the throttle valve to
supply air to the air chamber during engine idle.
The fuel for idle is provided by the injectors, the
quantity being determined by the ECU to suit the air
flow through the airflow sensor. The idle control unit
has provision for normal idle and also has a fast-idle
control device (FICD). The idle unit includes solenoidoperated valves.
The ECU sends signals to the solenoid valves to
increase the air supply when needed and also increases
the amount of fuel injected. This maintains idle speed
under varying engine conditions such as increased
electrical and mechanical load.
When the idle speed tends to drop due to an increased
electrical load on the engine (for example, when the


217-250_May 2chap 13

13/9/06

3:48 PM

Page 232

232 part two fuel and engine management

figure 13.26

Schematic arrangement of an electronic concentrated control system (ECCS)

HOLDEN LTD

Air regulator
The air regulator bypasses the throttle valve to control
the quantity of air for increasing the engine idling
speed during cold starting at lower temperatures.
Fuel system
The fuel tank has a low-pressure priming pump that
delivers fuel to the external high-pressure fuel pump.
The system includes a fuel damper and fuel filter.
A fuel-pressure regulator regulates pressure in the
system and returns surplus fuel to the tank through
the fuel return line (return-to-tank system). This
system employs a swirl pot to ensure adequate fuel
feed when the fuel level in the tank is low.
figure 13.27

Section through a hot-wire-type airflow
sensor FORD

headlamps are switched on), the solenoid of the auxiliary
air control (AAC) valve is energised to provide
additional air (and fuel) to maintain engine idle speed.
When the air conditioner is switched on, an increased
mechanical load is placed on the engine. The ECU then
energises the solenoid valve of the fast-idle control
device (FICD) to provide even more air (and fuel) to
maintain engine idle rpm under the additional load.

Fuel pump control

The ECU together with the ignition switch controls the
operation of the electric fuel pump, so that it operates
only when needed and not continuously with the
ignition switch turned on and the engine stopped.
If a ‘start’ signal is not received by the ECU after
the ignition switch is turned on, the fuel pump will
operate for a short period only. Therefore, if the engine
fails to start or the ignition switch is accidentally left
on, the fuel pump will be stopped.


217-250_May 2chap 13

13/9/06

3:49 PM

Page 233

chapter thirteen electronic fuel injection and engine management

The fuel pump will continue to operate as long as
the engine is running, but when the engine stops, the
fuel pump will automatically stop after about one
second.
■ Some systems also use a roll-over switch or air-bag
deployment signal to switch the fuel pump off in an
accident situation.
Carbon canister
A carbon canister is also shown in the system. This has

a connection to the engine’s air intake system.
Evaporative emissions are able to be stored in the
canister and later burnt by the engine.

233

of the light passing through the holes in the disc is
used as a means of sensing speed. It can also be used
to sense the angular position of the disc.
Distributor sensor
A sensor fitted in a distributor is shown in Figure
13.29. This consists of two parts: a disc, or rotor plate,
and a sensor unit which carries the diodes. The rotor
has 360 slits spaced at 1° intervals. These are used to
provide a light signal at each 1° of disc rotation, and
this is used for engine rpm.

Control system
The function of the ECU is to receive and process
signals from a number of sensors, to compare the
signals with data in its memory, and then to send
signals to the fuel and ignition systems and other
components. The electronic components and circuitry
are contained within a metal container (Figure 13.2).
The electrical cables are connected to the ECU by
means of multipin connectors.
Crank-angle sensor
The crank-angle sensor for this system is located in the
distributor. This detects both engine rpm and crank
angle, which is the angular position of the crankshaft.

An optical method of sensing is used. With this
arrangement a perforated disc is used, together with a
light-emitting diode (LED) as a light source and a
photodiode as a light sensor.
A simplified arrangement is shown in Figure 13.28.
The disc is rotated between the diodes, and light from
the LED passes through the holes in the disc onto the
photodiode which acts as a light sensor. The frequency

figure 13.29

Distributor with an optical sensor

HOLDEN LTD

The disc also has four slots at 90° intervals for a
four-cylinder engine, and six slots at 60° for a sixcylinder engine. The signal from these slots is used
for ignition and injection timing. The light signals
from both sets of slots are changed to voltage pulses
by the photodiode and are then directed to the
ECU.
Oxygen sensor
The exhaust system has a catalytic converter and a
muffler. An oxygen sensor is fitted in the exhaust
system ahead of the catalytic converter.
This is a closed-loop system, and the oxygen sensor
provides signals to the ECU to indicate the condition
of the exhaust gases. This enables the ECU to make
corrections to the fuel being injected so that the
optimum air–fuel ratio can be provided.

Coolant-temperature sensor
This is fitted into the water-jackets of the engine. It
senses coolant temperature and signals this to the
ECU, which can adjust the fuel mixture and ignition to
suit a hot or cold engine.
Vehicle-speed sensor

figure 13.28

Simplified optical crank-angle sensor

Signals from a vehicle-speed sensor are supplied to the
ECU so that it can make the necessary adjustments for
vehicle speed.


217-250_May 2chap 13

13/9/06

3:49 PM

Page 234

234 part two fuel and engine management
Neutral switch
The starter neutral switch for automatic transmission is
connected to the ECU.
■ The starter neutral switch is sometimes called the
starter inhibitor switch or gearshift position switch.

Ignition system
A signal is sent from the ECU to the power transistor
each time a spark is required for ignition. The built-in
power transistor amplifies the signal from the ECU. It
then temporarily breaks the primary circuit of the
ignition coil and so induces the high voltage in the
secondary coil that produces the spark at the spark plug.
Distributor
As well as the crank-angle sensor previously mentioned, the distributor consists of a normal rotor,

distributor cap and cables which distribute the hightension voltage to the spark plugs in correct firing
order. The distributor has no advance mechanism, as
all ignition timing is taken care of by the ECU.

Sequential multipoint
fuel injection system
Figure 13.30 shows the location, on a vehicle, of the
components of a sequential multipoint fuel injection
system. The fuel and the ignition are centrally
controlled, as is the variable valve timing mechanism
and a number of other items. This is a total enginemanagement system.
The various parts of the air and fuel systems, and
their location, are shown in the illustration. These are
noted below:

1
engine ECU

2
ignition coil

with igniter
3
airflow meter

18
camshaft timing oil
control valve

19
injector

4
VSV (for EVAP)

17
knock sensor

16
crankshaft position
sensor
15
air–fuel ratio sensor
(bank 1, sensor 1)
14
air–fuel ratio sensor
(bank 2, sensor 1)
5
DLC

13

three-way
catalytic converter
12
heated oxygen sensor
(bank 1, sensor 2)
11
heated oxygen sensor
(bank 2, sensor 2)

10
water temp. sensor

figure 13.30

7
ISC valve

6
throttle position
sensor

9
camshaft position
sensor
8
neutral start switch

The location of the components of a returnless EFI (and the engine management system)

TOYOTA

217-250_May 2chap 13

13/9/06

3:49 PM

Page 235

chapter thirteen electronic fuel injection and engine management

1. Engine ECU. Reads inputs from sensors and
delivers outputs to actuators to control the system.
2. Ignition coil with igniter. Supplies the spark to
ignite the fuel charge. This is a coil-on-plug
arrangement which reduces high voltage loss.
3. Airflow meter. Provides air flow information to
the ECU.
4. VSV (vacuum switching valve). ECU-controlled
evaporative emission control device which
connects the purge canister to the intake manifold.
5. DLC (data link connector). Allows codes to be
downloaded and actuators to be checked by
providing a connection for a scan tool.
6. Throttle position sensor. Tells the ECU the
position of the throttle.
7. ISC (idle speed control) valve. A rotary-solenoid
type valve that is used to control the idle and fastidle speeds.
8. Neutral start switch. Tells the ECU the gear

position selected.
9. Camshaft position sensor. Tells the ECU the
position of the camshaft to enable coordination of
ignition and injection timing.
10. Water temperature sensor. Provides coolant
temperature information to the ECU.
11, 12. Heated oxygen sensors. Provide post-catalyticconverter, exhaust-gas oxygen information to the
ECU.
13. Three-way catalytic converter. Treats carbon
monoxide, hydrocarbons and oxides of nitrogen
exhaust gas emissions.
14, 15. Air–fuel ratio sensors. Provide pre-catalyticconverter exhaust-gas-oxygen information to the
ECU.
16. Crankshaft position sensor. Tells the ECU the
crank-angle of the crankshaft.
17. Knock sensor. Detects fuel detonation (pinging) so
that the ECU can retard ignition timing to prevent
piston damage.
18. Camshaft timing oil control valve. Varies the
intake valve timing to provide optimum engine
performance for various conditions.
19. Injector. Sprays the fuel into the inlet port.

235

Schematic diagram of the system
The complete system is illustrated in schematic form in
Figure 13.31. Features of the system are described in
the following paragraphs.
Air system

This is similar in operation to the air system of the
L-Jetronic electronic fuel injection covered previously
with the exception of the idle-speed control
mechanism. A rotary-solenoid idle-speed control valve
is used instead (Figure 13.32).
This unit is operated by a series of pulses from the
ECU. The ECU can turn the pintle in a forward or
reverse direction by changing the polarity of the
windings. The pintle moves in or out and, in doing so,
regulates the volume of air that bypasses the throttle
valve.
Fuel system
This system is a returnless fuel system. The fuel pump,
fuel filter, and pressure regulator are designed as an
assembly as shown in Figure 13.33. The complete
assembly is mounted inside the fuel tank. The pump
provides fuel to the fuel delivery pipe (fuel rail) via a
pulsation damper unit. There is no return line to the
fuel tank.
An injector for the system is shown in Figure 13.34.
This is designed with twelve holes in the nozzle to
improve the atomisation of the fuel.
Control system
The ECU is programmed to receive inputs from
various sources and then provide outputs. The inputs
and outputs for this system are shown on the chart in
Figure 13.35.
The ECU receives inputs from the sensors shown
on the left of the illustration and sends controlling
signals to the actuators shown on the right. As can be

seen from the chart, the ECU receives signals from
many sources, not all being directly related to the
engine. However, many things have an influence on
the engine, such as preventing it from starting unless
the security system provides the right signals.

Other features of
engine control systems
There are a number of variations of the multipointinjection systems discussed. It is not possible to cover all
these, but some are noted in the following paragraphs.


217-250_May 2chap 13

13/9/06

3:49 PM

Page 236

236 part two fuel and engine management

ignition
switch

combination
meter

power steering
oil pressure

switch

battery

check engine
warning light

circuit opening relay

engine ECU
VSV
(for EVAP)

airbag sensor
assembly

camshaft
position
sensor

throttle
position
sensor

charcoal
canister

DLC3

fuel pump

air conditioner
amplifier

camshaft
timing oil
control
valve

airflow meter

air–fuel ratio
sensors

DIS

ISC valve
injector
air

WT

air cleaner
knock sensor

crankshaft position
sensor

figure 13.31

water temp.
sensor

A schematic diagram of an EFI and the engine management system

Modes of injection
There are four different modes of injection.
1. Continuous. Injector sprays continuously and the
flow rate is controlled to suit the load and speed of
the engine. Usually found only on older model
vehicles.
2. Simultaneous. All injectors operate at the same time
and inject once for each revolution of the engine.
3. Sequential. Injectors are arranged to operate in a
sequence that follows the firing order of the engine.
4. Grouped (banked). Injectors operate in groups that
follow the firing order of the engine. For example,
in a two-bank system for a six-cylinder engine,

heated oxygen
sensors

TOYOTA

injectors 1,5,3 are grouped to operate together
followed by 6,2,4.
Figure 13.36 shows the basic wiring diagrams for
simultaneous, sequential and grouped modes. The
ECU controls the injectors by completing the circuits
to earth. For Figure 13.36(a), all the injectors will

operate at once. For Figure 13.36(b), each injector can
be operated independently, and for Figure 13.36(c), the
injectors can only be operated as groups of three.
Synchronous and asynchronous injection
With synchronous injection, the operation of the
injectors is synchronised to the speed of the engine.


217-250_May 2chap 13

13/9/06

3:49 PM

Page 237

chapter thirteen electronic fuel injection and engine management

237

fuel inlet
to ECU
electrical
connector

winding

armature
rotates

winding

fine thread
(a)
pintle can move
up and down but
can’t rotate

(b)
by-pass air

figure 13.34

A twelve-hole injector
(a) underside of nozzle (b) complete injector
TOYOTA

asynchronous pulses as deemed necessary by the ECU
for particular conditions.

throttle valve

figure 13.32

A rotary-solenoid type of idle-speed control
valve

Intake manifold design

to engine

pressure
regulator

fuel filter

fuel pump
fuel sender
gauge

figure 13.33

■ Asynchronous pulses could be used during acceleration, wide-open throttle and cold starting.

A fuel pump assembly for a returnless fuel
system TOYOTA

The ECU normally uses an ignition pulse, or crankshaft reference signal, to initiate injection.
With asynchronous injection, injection is not tied to
the ignition system, crankshaft speed or position.
Injectors operate on a time basis. The ECU determines
the time between injection pulses.
Most systems are synchronous but will employ

The intake manifold used with multipoint EFI systems
carries air only and not a mixture of air and fuel, so the
manifold can be designed specially to suit air flow.
Because the fuel is injected at the intake ports, the
manifold requires no heating to keep the air–fuel
mixture atomised, and so it is designed with all its

pipes or branches of equal or almost equal length.
Also, the pipes can be made of a particular length to
make most use of the ram effect produced by air-intake
pulsations.
To provide some storage and even distribution of
air, an air or plenum chamber is located between the
throttle body and the air-intake pipes or intake
manifold.
■ Refer to Chapter 16: Induction systems, turbochargers and superchargers for more information on
intake manifolds.
Detonation sensor
A detonation sensor can be fitted to the system. It is
screwed into the side of the cylinder block (Figure
13.37). It detects vibrations that occur as the result of


217-250_May 2chap 13

13/9/06

3:49 PM

Page 238

238 part two fuel and engine management
sensors

actuators

airflow meter

EFI
no. 1 injector
no. 2 injector
no. 3 injector
no. 4 injector

intake air temp. sensor
water temp. sensor
throttle position sensor

ESA

crankshaft position sensor

ignition coil with igniter
camshaft position sensor

spark plugs

air–fuel ratio sensor
(bank 1, sensor 1)

engine
ECU
VVT-i

air–fuel ratio sensor
(bank 2, sensor 1)

camshaft timing oil
control valve

heated oxygen sensor
(bank 1, sensor 2)
heated oxygen sensor
(bank 2, sensor 2)

ISC
control valve

knock sensor
air conditioner amplifier
fuel pump control
neutral start switch

circuit opening relay

air-bag sensor assembly
combination meter

oxygen sensor heater
control
air–fuel ratio sensor
bank 1, sensor 1
bank 2, sensor 1
heated oxygen sensor
bank 1, sensor 2
bank 2, sensor 2

• vehicle speed signal
Ignition switch
• starting signal
• ignition signal

power steering oil
pressure switch

evaporation emission
control

transponder key
amplifier

VSV (for EVAP)

unlock warning switch
air conditioner cut
off control

rear window defogger
relay

air conditioner amplifier

taillight relay
EFI main relay

stop light switch

data link connector

check engine warning light

EFI main relay

figure 13.35

Engine management system input/output logic chart

battery
TOYOTA


217-250_May 2chap 13

13/9/06

3:49 PM

Page 239

chapter thirteen electronic fuel injection and engine management

239

injectors

figure 13.36

+

+

+

ECU

ECU

ECU

(a) Simultaneous

(b) Sequential

(c) Banked

Wiring diagrams for different injector modes

detects detonation it retards the ignition timing at each
PIP signal in steps of between 1° and 2° until the
knocking stops.
When the knocking ceases, the ECU advances the
timing in steps of only 1/4° until it detects knocking
again.
figure 13.37

The detonation or knock sensor picks up
vibrations caused by detonation HOLDEN LTD

combustion pressures in the combustion chambers, and
converts the vibrations into electrical signals.
If detonation occurs, abnormal vibration will result.
This will be detected by the sensor, and a signal will be
sent to the ECU to temporarily retard the ignition
timing.
Figure 13.38 shows how the ECU responds to the
knock sensor in a six-cylinder engine. When the ECU

■ Each PIP signal represents 60° of crankshaft
rotation.
Karman vortex airflow sensor
Vane and hot-wire airflow sensors have already been
discussed, but there is a third type, known as a Karman
vortex sensor. Its operating principle is shown in
Figure 13.39.
All the air entering the system passes through the
sensor, which is shaped so that it creates a vortex or
swirling of the air. A transmitter on one side of the

Degrees of advance

knock identified
timing retarded
in steps
1–2∞ dependent
on speed/load

knock again

identified
timing ramps up in
small steps until
knock again identified

0.25∞

knock stops

Time (PIP signals)

figure 13.38

The response of the ECU to a knock-sensor signal

FORD


217-250_May 2chap 13

13/9/06

3:49 PM

Page 240

240 part two fuel and engine management
As well as being used to determine fuel injection
quantity, this information is used to control ignition
timing and various transmission functions.

MAT sensor
The manifold air temperature (MAT) sensor (Figure
13.41) is a thermistor (a resistor that reduces its
resistance with temperature increase). It is screwed
into the intake manifold to measure the manifold air
temperature and to signal it to the ECU. The intakeair temperature is used by the ECU in calculating the
injector pulse width.
figure 13.39

Karman vortex airflow sensor

FORD

sensor sends ultrasonic waves to a receiver on the other
side. The waves are distorted as they pass through the
swirling air. After reaching the receiver, they are
changed to electric pulses and sent to the ECU.
■ The arrangement detects changes in air movement
and uses it to measure the rate of air flow.

figure 13.41

A MAT sensor is mounted in the intake
manifold to measure temperature
HOLDEN LTD

MAF sensor

MAP sensor

The mass airflow (MAF) sensor (Figure 13.40) directly
measures the mass of air entering the engine. A temperature probe inside a bypass air passage measures
the ambient air temperature. A wire element (hot wire
probe), beside the temperature probe is heated to a
constant temperature above ambient temperature by an
electrical current. The air entering the engine cools the
element thus requiring an increase in current flow to
maintain the same temperature difference. This
information is processed by the ECU to calculate the
mass of air entering the engine.

The manifold absolute pressure (MAP) sensor (Figure
13.42) measures the absolute pressure in the intake
manifold. For practical purposes, this is referred to as
the manifold vacuum. The sensor is responsive to
manifold vacuum and also to barometric pressure. The
air–fuel ratio, the ignition timing and the idle speed
can all be modified by the ECU as a result of the MAP
sensor signal.

mass airflow
sensor
hot wire
probe

connector

temperature
probe

air flow

figure 13.40

A MAF sensor directly measures the mass of
air entering the engine FORD

figure 13.42

A MAP sensor for signalling intake manifold
pressure FORD


217-250_May 2chap 13

13/9/06

3:49 PM

Page 241

chapter thirteen electronic fuel injection and engine management

241

Duty solenoid air-control valve
Both bimetal and rotating solenoid air-control valves
(which are used for idle-air control) have already been
discussed. There is also another type, known as a dutysolenoid air-control valve. Its operating principle is
shown in Figure 13.43.

A spring tries to push the valve towards one end of
the bore (closed) and the solenoid tries to push it
towards the other end (open). The ECU pulses the
solenoid coil on and off. The higher the duty cycle of
the solenoid, the stronger it becomes and the valve
opens further. As the valve opens, more air is allowed
to bypass the throttle valve and the engine speed is
increased.
electrical
connector
diaphragm
seal

figure 13.44
valve body

Simplified arrangement of throttle-body
injection

valve plate

fuel from the injector to provide the correct air–fuel
ratio.
(a)
solenoid
windings

Injector
air flow inlet
air flow outlet

An injector is shown in Figure 13.45. The injector is
similar to that used for multipoint-injection, and
includes a nozzle and a spring-loaded plunger operated
by a solenoid. When the plunger is held against its seat

(b)

figure 13.43

Idle-air control valve assembly (duty solenoid
type)
(a) sectional view (b) valve assembly FORD

Throttle-body injection (TBI)
Throttle-body fuel injection systems (single-point
injection) have a single injector, or in some systems,
two fuel injectors in the throttle-body assembly. The
throttle-body assembly is fitted to the flange of the
engine intake manifold.
A simplified arrangement of a throttle-body injector
is shown in Figure 13.44. In operation, fuel under
pressure is supplied to the injector. When the injector
opens, fuel is sprayed into the intake air passing
through the throttle body.
The air–fuel mixture then passes through the intake
manifold to the engine. The throttle valve controls
the air flow into the manifold, and the ECU controls the

figure 13.45

Injector for throttle-body injection

FORD