electric BMW 3 SERIES 1990 E30 Owner's Manual

information on removing and refitting the
intake manifold, refer to Chapter 2A.
The throttle valve inside the throttle body or
carburettor is actuated by the accelerator
cable. When you depress the accelerator
pedal, the throttle plate opens and airflow
through the intake system increases.
On fuel injection systems, a flap inside the
airflow meter opens wider as the airflow
increases. A throttle position switch attached
to the pivot shaft of the flap detects the angle
of the flap (how much it’s open) and converts
this to a voltage signal, which it sends to the
computer.
Fuel system
On carburettor models, the fuel pump
supplies fuel under pressure to the
carburettor. A needle valve in the float
chamber maintains the fuel at a constant
level. A fuel return system channels excess
fuel back to the fuel tank.
On fuel injection models, an electric fuel
pump supplies fuel under constant pressure
to the fuel rail, which distributes fuel to the
injectors. The electric fuel pump is located
inside the fuel tank on later models, or beside
the fuel tank on early models. Early models
also have a transfer pump located in the fuel
tank. The transfer pump acts as an aid to the
larger main pump for delivering the necessary
pressure. A fuel pressure regulator controls
the pressure in the fuel system. The fuel
system also has a fuel pulsation damper
located near the fuel filter. The damper
reduces the pressure pulsations caused by
fuel pump operation, and the opening and
closing of the injectors. The amount of fuel
injected into the intake ports is precisely
controlled by an Electronic Control Unit (ECU
or computer). Some later 5-Series models
have a fuel cooler in the return line.
Electronic control system (fuel
injection system)
Besides altering the injector opening
duration as described above, the electronic
control unit performs a number of other tasks
related to fuel and emissions control. It
accomplishes these tasks by using data
relayed to it by a wide array of information
sensors located throughout the enginecompartment, comparing this information to
its stored map, and altering engine operation
by controlling a number of different actuators.
Since special equipment is required, most
fault diagnosis and repair of the electronic
control system is beyond the scope of the
home mechanic. Additional information and
testing procedures for the emissions system
components (oxygen sensor, coolant
temperature sensor, EVAP system, etc.) is
contained in Chapter 6.
2 Fuel injection system-
depressurising
1
Warning: Fuel is extremely
flammable, so take extra
precautions when you work on
any part of the fuel system. Don’t
smoke or allow open flames or bare light
bulbs near the work area. Also, don’t work
in a garage where a natural gas-type
appliance with a pilot light is present.
1Remove the fuel pump fuse from the main
fuse panel (see illustrations). Note:Consult
your owner’s handbook for the exact location
of the fuel pump fuse, if the information is not
stamped onto the fusebox cover.
2Start the engine, and wait for it to stall.
Switch off the ignition.
3Remove the fuel filler cap to relieve the fuel
tank pressure.
4The fuel system is now depressurised.
Note:Place a rag around fuel lines before
disconnecting, to prevent any residual fuel
from spilling onto the engine(see
illustration).
5Disconnect the battery negative cable
before working on any part of the system.
Caution: If the radio in your
vehicle is equipped with an anti-
theft system, make sure you
have the correct activation code
before disconnecting the battery. Refer to
the information on page 0-7 at the front of
this manual before detaching the cable.
Note: If, after connecting the battery, the
wrong language appears on the instrument
panel display, refer to page 0-7 for the
language resetting procedure.
3 Fuel pump/fuel pressure-
check
3
Warning: Fuel is extremely
flammable, so take extra
precautions when you work on
any part of the fuel system. Don’t
smoke, or allow open flames or bare light
bulbs, near the work area. Also, don’t work
in a garage where a natural gas-type
appliance with a pilot light is present.
Carburettor engines
1To test the fuel pump, it will be necessary to
connect a suitable pressure gauge between
the fuel pump outlet, and the carburettor
supply pipe. For this particular test, the fuel
return valve, which is normally connected in
the fuel line from the fuel pump to the
carburettor, mustbe bypassed.
2With the engine running at idle speed, the
pump pressure should be between 0.1 and
0.3 bars.
3Should a pressure gauge not be available, a
simpler (but less accurate) method of testing
the fuel pump is as follows.
4Disconnect the outlet hose from the fuel
pump.
5Disconnect the LT lead from the coil, to
prevent the engine firing, then turn the engine
over on the starter. Well-defined spurts of fuel
should be ejected from the outlet hose.
Fuel injection engines
Note 1:The electric fuel pump is located
inside the fuel tank on later models, or beside
the fuel tank on early models. Early models are
also equipped with a transfer pump located in
the fuel tank. The transfer pump feeds the
main pump, but can’t generate the high
pressure required by the system.
Note 2:The fuel pump relay on Motronic
systems is activated by an earth signal from
the Motronic control unit (ECU). The fuel
pump operates for a few seconds when the
ignition is first switched on, and then
continues to operate only when the engine is
actually running.
Fuel and exhaust systems 4•3
2.4 Be sure to place a rag under and
around any fuel line when disconnecting2.1b Removing the fuel pump fuse on
5-Series models2.1a Removing the fuel pump fuse on
3-Series models
4

19Depressurise the fuel system (see Sec-
tion 2).
20Detach the battery negative cable.
Caution: If the radio in your
vehicle is equipped with an anti-
theft system, make sure you
have the correct activation code
before disconnecting the battery. Refer to
the information on page 0-7 at the front of
this manual before detaching the cable.
Note: If, after connecting the battery, the
wrong language appears on the instrument
panel display, refer to page 0-7 for the
language resetting procedure.
21Detach the fuel feed hose from the fuel
rail, and attach a fuel pressure gauge directly
to the hose. Note:If the tee fitting is still
connected to the gauge, be sure to plug the
open end.
22Reconnect the battery.
23Using a jumper wire, bridge the terminals
of the fuel pump relay.
24Turn the ignition switch on to operate the
fuel pump.
25Note the pressure reading on the gauge,
and compare the reading to the fuel pump
pressure listed in this Chapter’s Specifica-
tions.
26If the indicated pressure is less than
specified, inspect the fuel line for leaks
between the pump and gauge. If no leaks are
found, renew the fuel pump.
27Turn the ignition off and wait five minutes.
Note the reading on the gauge, and compare
it to the fuel pump hold pressure listed in this
Chapter’s Specifications. If the hold pressure
is less than specified, check the fuel lines
between the pump and gauge for leaks. If no
leaks are found, renew the fuel pump.
28Remove the jumper wire. Relieve the fuel
pressure by opening the bleed valve on the
gauge and directing the fuel into a suitable
container. Remove the gauge and reconnect
the fuel line.
Transfer pump pressure check
29Depressurise the fuel system (see Sec-
tion 2).
30Detach the battery negative cable.
Caution: If the radio in your
vehicle is equipped with an anti-
theft system, make sure you
have the correct activation code
before disconnecting the battery. Refer to
the information on page 0-7 at the front of
this manual before detaching the cable.
Note: If, after connecting the battery, the
wrong language appears on the instrument
panel display, refer to page 0-7 for the
language resetting procedure.
31Remove the transfer pump access plate
(on some models, it’s located under the rear
seat cushion - on others, it’s located under
the carpet in the luggage compartment).
Disconnect the output hose from the transfer
pump, and connect a fuel pressure gauge to
the outlet pipe.
32Reconnect the battery.33Using a jumper wire, bridge the terminals
of the fuel pump relay.
34Turn the ignition switch on to operate the
fuel pump.
35Note the pressure reading on the gauge,
and compare to the value listed in this
Chapter’s Specifications.
36If the indicated pressure is less than
specified, renew the transfer pump.
Fuel pump relay check
37Switch on the ignition.
38Using a voltmeter, probe the following
terminals from the back of the relay electrical
connector. Check for battery voltage at
terminal 30 (M20 and M30 engines) or
terminal 15 (M10 and M40 engines). Note:If
there is no voltage on models with luggage
compartment-mounted batteries, check for a
faulty fusible link. The 50-amp link is about
6 inches from the battery, in a black wire.
39Turn the ignition off, and disconnect the
relay from the electrical connector. Using a
voltmeter, probe the connector terminals that
correspond to fuel pump relay pins 85 (-) and
86(+) on M20 and M30 engines, or terminal 50
and earth on M10 and M40 engines. Have an
assistant turn the engine over on the starter,
and observe the voltage reading. Battery
voltage should be indicated.
40If there is no voltage, check the fuse(s)
and the wiring circuit for the fuel pump relay. If
the voltage readings are correct, and the fuel
pump only runs with the jumper wire in place,
then renew the relay.
41If the fuel pump still does not run, check
for the proper voltage at the fuel pump
terminals (see Section 4). If necessary, renew
the fuel pump.
4 Fuel pump, transfer pump
and fuel level sender unit-
removal and refitting
2
Warning: Fuel is extremely
flammable, so take extra
precautions when you work on
any part of the fuel system. Don’t
smoke, or allow open flames or bare light
bulbs, near the work area. Also, don’t work
in a garage where a natural gas-type
appliance with a pilot light is present.
Fuel pump (carburettor engines)
1Disconnect the battery negative cable.
Disconnect both hoses from the pump, and
unscrew and remove the two securing nuts
(see illustration).
2Carefully withdraw the pump from the
cylinder head. If it’s stuck, a slight downward
tap on the thick insulating distance piece with
a piece of wood, should free it.
3Remove the two thin gaskets.
4The fuel pump is a sealed unit, and it is not
possible to renew any of the internal
components. Should an internal fault occur, it
must be renewed complete.5Refitting is a reversal of the removal
procedure, but renew the thin gaskets each
side of the insulating distance piece, and
tighten the fuel pump down evenly to the
torque stated in the Specifications. On no
account alter the thickness of the distance
piece, or the correct operation of the fuel
pump will be upset.
Fuel pump (fuel injection
engines)
Note 1: The electric fuel pump is located
inside the fuel tank on later models with the
Motronic system, or adjacent to the fuel tank
on the L-Jetronic system. The early models
are also equipped with a transfer pump
located in the fuel tank. The transfer pump
feeds the larger main pump, which delivers
the high pressure required for proper fuel
system operation.
Note 2: The fuel level sender unit is located in
the fuel tank with the transfer pump on early
models, or with the main fuel pump on later
models.
6Depressurise the fuel system (see Sec-
tion 2) and remove the fuel tank filler cap to
relieve pressure in the tank.
7Disconnect the battery negative cable.
Caution: If the radio in your
vehicle is equipped with an anti-
theft system, make sure you
have the correct activation code
before disconnecting the battery. Refer to
the information on page 0-7 at the front of
this manual before detaching the cable.
Note: If, after connecting the battery, the
wrong language appears on the instrument
panel display, refer to page 0-7 for the
language resetting procedure.
Externally-mounted fuel pump
8Raise and support the vehicle.
9Remove the two rubber boots that protect
the fuel pump connectors, and disconnect the
wires from the pump (see illustration).
10Using hose clamps, pinch shut the fuel
hoses on each side of the fuel pump. If you
don’t have any hose clamps, wrap the hoses
with rags, and clamp them shut with self-
locking pliers, tightened just enough to
prevent fuel from flowing out.
11Disconnect the hoses from the pump.
12Remove the fuel pump mounting screws
Fuel and exhaust systems 4•5
4.1 Fuel pump on carburettor engines
4

and clamps, and remove the fuel pump from
the under the vehicle.
13Refitting is the reverse of removal.
In-tank fuel pump or transfer pump
14On some models, access to the fuel pump
is gained by removing the rear seat cushion.
On other models, access is gained by
removing the carpet from the luggage
compartment.
15Remove the screws from the fuel pump
access cover (see illustration).
16Remove the cover.
17Locate the fuel pump and sender unit
electrical connectors (see illustrations)andunplug them. Also, disconnect the fuel inlet
and return lines.
18On some models, the assembly must be
rotated anti-clockwise to disengage the
locking lugs from the fuel tank (see
illustration). On other models, the assembly
is secured to the tank with nuts (see
illustration). Carefully lift the assembly from
the fuel tank (see illustrations). It may be
necessary to twist the assembly slightly, to
get the float to clear the opening.
19On early models, remove the transfer
pump mounting screws and clamps, and
separate the transfer pump from the
assembly.
20Refitting is the reverse of removal. If the
gasket between the fuel pump and fuel tank is
dried, cracked or damaged, renew it.
Fuel level sender unit - check
and renewal
21Remove the main fuel pump or transfer
pump (as described previously) along with the
fuel level sender unit.
22Connect an ohmmeter across the
designated terminals, and check for the
4•6 Fuel and exhaust systems
4.18e Exploded view of the fuel pump
assembly on later Motronic systems4.18d . . . then pull the fuel pump straight
up and out of the turret at the bottom of
the fuel tank (keep all the fuel lines intact)4.18c On later Motronic systems, first
remove the fuel level sender unit . . .
4.18b On models with mounting nuts,
remove the nuts (arrowed) to release the
assembly from the fuel tank4.18a On models with locking lugs, use
two screwdrivers to rotate the assembly
out of the notches
4.17b To unplug the connector, prise the
bracket until the notch aligns with the slot
on the retaining clip, and release the
connector from the assembly
4.17a Transfer pump (1) and fuel level
sender unit (2) electrical connectors on an
early Motronic system4.15 Remove the fuel pump cover screws
(arrowed) and lift the cover off the floor of
the vehicle (on some models, the fuel
pump cover is located under the rear seat
- on other models it’s located in the
luggage compartment)4.9 Lift up the rubber boots (arrowed) and
detach the electrical connectors from the
fuel pump

correct resistance. On L-Jetronic and early
Motronic systems, follow the table below. On
later Motronic systems, connect the
ohmmeter probes onto the fuel level sender
unit terminals that correspond to pins 1 and 3
on the electrical connector (see illustrations).
The resistance should decrease as the
plunger rises.
L-Jetronic and early Motronic systems
Terminals Float position Resistance
G and 31 Slowly moving Resistance
fromthe EMPTY slowly
position to the decreases
FULL position
EMPTY 71.7 ± 2.3 ohms
FULL 3.2 ± 0.7 ohms
W and 31 EMPTY (low Continuity
fuel warning)
23If the resistance readings are incorrect,
renew the sender unit.
24Refitting is the reverse of removal.
5 Fuel lines and fittings-
repair and renewal
3
Warning: Fuel is extremely
flammable, so take extra
precautions when you work on
any part of the fuel system. Don’t
smoke, or allow open flames or bare light
bulbs, near the work area. Don’t work in a
garage where a natural gas-type appliance
(such as a water heater or clothes dryer)
with a pilot light is present. If you spill any
fuel on your skin, rinse it off immediately
with soap and water. When you perform
any kind of work on the fuel system, wear
safety glasses, and have a fire
extinguisher on hand.
1Always disconnect the battery negative
cable, and (on fuel injection models)
depressurise the fuel system as described in
Section 2, before servicing fuel lines or
fittings.
2The fuel feed, return and vapour lines
extend from the fuel tank to the engine
compartment. The lines are secured to the
underbody with clip and screw assemblies.These lines must be occasionally inspected
for leaks, kinks and dents (see illustration).
3If evidence of dirt is found in the system or
fuel filter during dismantling, the lines should
be disconnected and blown out. On fuel
injection models, check the fuel strainer on
the in-tank fuel pump for damage and
deterioration.
4Because fuel lines used on fuel injection
vehicles are under high pressure, they require
special consideration. If renewal of a rigid fuel
line or emission line is called for, use welded
steel tubing meeting BMW specification or its
equivalent. Don’t use plastic, copper or
aluminium tubing to renew steel tubing. These
materials cannot withstand normal vehicle
vibration.
5When renewing fuel hoses, be sure to use
only hoses of original-equipment standard.6 Fuel tank-
removal and refitting
3
Warning: Fuel is extremely
flammable, so take extra
precautions when you work on
any part of the fuel system. Don’t
smoke, or allow open flames or bare light
bulbs, near the work area. Also, don’t work
in a garage where a natural gas-type
appliance with a pilot light is present.
When you perform any kind of work on the
fuel system, wear safety glasses, and have
a fire extinguisher on hand. If you spill any
fuel on your skin, clean it off immediately
with soap and water.
Note: To avoid draining large amounts of fuel,
make sure the fuel tank is nearly empty (if
possible) before beginning this procedure.
1Remove the fuel tank filler cap to relieve
fuel tank pressure.2On fuel injection models, depressurise the
fuel system (see Section 2).
3Detach the battery negative cable.
Caution: If the radio in your
vehicle is equipped with an anti-
theft system, make sure you
have the correct activation code
before disconnecting the battery. Refer to
the information on page 0-7 at the front of
this manual before detaching the cable.
Note: If, after connecting the battery, the
wrong language appears on the instrument
panel display, refer to page 0-7 for the
language resetting procedure.
4Remove the tank drain plug (see
illustration)and drain the fuel into an
approved fuel container. If no drain plug is
fitted, it should be possible to syphon the fuel
out (not by mouth), otherwise the fuel will have
to be drained during the removal operation.
5Unplug the fuel pump/sender unit electrical
connector (as applicable) and detach the fuel
feed, return and vapour hoses (see Section 4).
Where applicable, remove the rear seat
cushion for access.
6Remove the fuel tank shield (see
illustration).
7Detach the fuel filler neck and breather
hoses.
8Raise and support the vehicle. On some
models, it will also be necessary to remove
the exhaust system and propeller shaft.
9Support the tank with a trolley jack.
Fuel and exhaust systems 4•7
4.22b Fuel level sender unit terminal
designations on later Motronic systems -
check the sender unit resistance across
terminals 1 and 3 of the connector
1 Fuel level sender unit earth
2 Warning light
3 Sender unit
4 Fuel pump earth
5 Fuel pump4.22a Fuel level sender unit terminal
designations on L-Jetronic and early
Motronic systems
6.4 Remove the tank drain plug (arrowed)
and drain the fuel into a suitable container
5.2 When checking the fuel lines, don’t
overlook these short sections of fuel hose
attached to the main fuel rail - they’re a
common source of fuel leaks
4

6Unscrew the four nuts retaining the air
cleaner to the carburettor, and remove the
metal ring (see illustrations).
7Unscrew the nut from the mounting bracket
(see illustration).
8Lift the air cleaner from the carburettor, and
disconnect the crankcase ventilation hose
(see illustration). If necessary, prise the
sealing ring from the bottom of the air cleaner.
9Refitting is a reversal of removal, but align
the arrow on the cover with the arrow on the
inlet tube (see illustration).
Fuel injection engines
10Detach the air intake duct from the front
side of the air cleaner.11Detach the duct between the air cleaner
and the throttle body.
12Remove the air filter (see Chapter 1).
13Unplug the electrical connector from the
airflow meter (see Section 12).
14Remove the air cleaner mounting bolts
(see illustration)and lift the air cleaner
assembly from the engine compartment.
15Refitting is the reverse of removal. Ensure
that all ducts are securely refitted, or air leaks
will result.
9 Accelerator cable- check,
adjustment and renewal
1
Check
1Separate the air intake duct from the
throttle body (fuel injection models) or remove
the air cleaner (carburettor models).
2Have an assistant depress the accelerator
pedal to the floor while you watch the throttle
valve. It should move to the fully-open
position.
3Release the accelerator pedal, and make
sure the throttle valve returns smoothly to the
fully-closed position. The throttle valve should
not contact the body at any time during its
movement; if it does, the unit must be renewed.
Adjustment
4Warm the engine to normal operating
temperature, then switch it off. Depress theaccelerator pedal to the floor twice, then
check the cable free play at the
carburettor/throttle body. Compare it to the
value listed in this Chapter’s Specifications.
5If the free play isn’t as specified, adjust it by
turning the adjustment nut (see illustration).
6Have an assistant help you verify the
throttle valve is fully open when the
accelerator pedal is depressed to the floor.
Renewal
Note:The following paragraphs describe the
procedure for fuel injection engines - the
procedure is similar on carburettor engines
7Disconnect the battery negative cable.
Fuel and exhaust systems 4•9
8.6b . . . and remove the metal ring8.6a Unscrew the four air cleaner-to-
carburettor nuts . . .8.4 Air cleaner inlet duct (1) and warm-air
hose (2)
9.5 To adjust the accelerator cable free
play, hold nut B stationary and turn nut A
(fuel injection engine shown)8.14 Remove the two nuts (arrowed) from
the air cleaner assembly (Motronic system
shown), and lift it off its mountings
8.8 Disconnecting the crankcase
ventilation hose from the air cleaner8.7 Air cleaner mounting bracket nut
(arrowed)8.9 Align the air cleaner cover arrows
when refitting
4

Caution: If the radio in your
vehicle is equipped with an anti-
theft system, make sure you
have the correct activation code before
disconnecting the battery. Refer to the
information on page 0-7 at the front of this
manual before detaching the cable.
Note: If, after connecting the battery, the
wrong language appears on the instrument
panel display, refer to page 0-7 for the
language resetting procedure.
8Loosen the cable adjuster locknuts, and
detach the cable from its support bracket
located on the intake manifold (see
illustration).
9Pinch the plastic retainer with a pair of
needle-nose pliers, and push it out of the
bracket (see illustration).10Pull the cable down through the slot and
away from the bracket (see illustrations).
11Working from underneath the driver’s side
of the facia, reach up and detach the
accelerator cable from the top of the pedal.
12Pull the cable through the bulkhead, from
the engine compartment side.
13Refitting is the reverse of removal. Adjust
the cable as described earlier.
10 Carburettor-
general information
1Early models are fitted with a Solex 2B4
carburettor, and later models are fitted with a
Solex 2BE carburettor. Both carburettors are
of downdraught, two-stage type. The first
stage is operated mechanically by the
accelerator pedal, and the second stage by
vacuum control.
2Each stage has its own float chamber, float
assembly and needle valve, designed to
reduce the effects of braking and centrifugal
forces.
3On the 2B4 version, the primary stage
choke valve is operated by an automatic
choke (a bi-metal spring which is electrically
heated) during the warm-up period. Warm-up
enrichment is also provided by a coolant-
operated thermal valve and air temperature-
controlled flow valve.
4On the 2BE version, an electronic controlunit is used to automatically adjust the
carburettor settings during warm-up and
normal temperature operation. The control
unit is located beneath the right-hand side of
the facia.
11 Carburettor-
removal and refitting
2
Removal
1Remove the air cleaner as described in
Section 8.
2Disconnect the accelerator cable from the
carburettor with reference to Section 9.
3On automatic transmission models,
disconnect the kickdown cable.
4Disconnect the wiring from the carburettor,
noting the location of each wire.
5Remove the screw, and disconnect the
earth cable from the throttle positioner
bracket (see illustration).
6Disconnect the vacuum hoses, noting that
the hose with the white tracer is located on
the white plastic ‘T’ piece, and the distributor
vacuum hoses are located on the side of the
carburettor (see illustration).
7On the 2B4 carburettor, disconnect and
plug the coolant hoses from the TM (thermal
starter) valve.
8Disconnect the fuel supply hose (see
illustration).
4•10 Fuel and exhaust systems
11.8 Disconnect the fuel supply hose
(arrowed)11.6 Note the locations of the carburettor
vacuum hoses (arrowed) before
disconnecting them11.5 Remove the screw, and disconnect
the carburettor earth cable (arrowed)
9.10b After the cable is off the throttle
valve assembly, remove the plastic
retainer from the cable
9.10a Rotate the throttle valve and remove
the cable end from the slotted portion of
the valve9.9 Pinch the plastic retainer, and push it
through the bracket recess on the throttle
valve9.8 Push the rubber grommet from the
rear, and separate the cable from the
bracket

Throttle positioner (2BE)
24Special tools are required to carry out a
comprehensive adjustment on the 2BE
carburettor. This work should therefore be left
to a BMW dealer.
13 Fuel injection -
general information
The fuel injection system is composed of
three basic sub-systems: fuel system, air
intake system and electronic control system.
Fuel system
An electric fuel pump, located inside the
fuel tank or beside the fuel tank, supplies fuel
under constant pressure to the fuel rail, which
distributes fuel evenly to all injectors. From
the fuel rail, fuel is injected into the intake
ports, just above the intake valves, by the fuel
injectors. The amount of fuel supplied by the
injectors is precisely controlled by an
Electronic Control Unit (ECU). An additional
injector, known as the cold start injector (L-
Jetronic and early Motronic systems only),
supplies extra fuel into the intake manifold for
starting. A pressure regulator controls system
pressure in relation to intake manifold
vacuum. A fuel filter between the fuel pump
and the fuel rail filters the fuel, to protect the
components of the system.
Air intake system
The air intake system consists of an air filter
housing, an airflow meter, a throttle body, the
intake manifold, and the associated ducting.
The airflow meter is an information-gathering
device for the ECU. These models are
equipped with the vane-type airflow meter. A
potentiometer measures intake airflow, and a
temperature sensor measures intake air
temperature. This information helps the ECU
determine the amount of fuel to be injected by
the injectors (injection duration). The throttle
plate inside the throttle body is controlled by
the driver. As the throttle plate opens, the
amount of air that can pass through the
system increases, so the potentiometer opens
further and the ECU signals the injectors to
increase the amount of fuel delivered to the
intake ports.
Electronic control system
The computer control system controls the
fuel system and other systems by means of
an Electronic Control Unit (ECU). The ECU
receives signals from a number of information
sensors which monitor such variables as
intake air volume, intake air temperature,
coolant temperature, engine rpm,
acceleration/deceleration, and exhaust
oxygen content. These signals help the ECU
determine the injection duration necessary for
the optimum air/fuel ratio. These sensors and
their corresponding ECU-controlled outputactuators are located throughout the engine
compartment. For further information
regarding the ECU and its relationship to the
engine electrical systems and ignition system,
refer to Chapters 5 and 6.
Either an L-Jetronic system or a Motronic
system is fitted. Later models have an
updated version of the original Motronic
system.
14 Fuel injection systems
L-Jetronic fuel injection system
The Bosch L-Jetronic fuel injection system
is used on most 3-Series models up to 1987,
and on most E28 (“old-shape”) 5-Series
models. It is an electronically-controlled fuel
injection system that utilises one solenoid-
operated fuel injector per cylinder. The system
is governed by an Electronic Control Unit
(ECU) which processes information sent by
various sensors, and in turn precisely
meters the fuel to the cylinders by
adjusting the amount of time that the injectors
are open.
An electric fuel pump delivers fuel under
high pressure to the injectors, through the fuel
feed line and an in-line filter. A pressure
regulator keeps fuel available at an optimum
pressure, allowing pressure to rise or fall
depending on engine speed and load. Any
excess fuel is returned to the fuel tank by a
separate line.
A sensor in the air intake duct constantly
measures the mass of the incoming air, and
the ECU adjusts the fuel mixture to provide an
optimum air/fuel ratio.
Other components incorporated in the
system are the throttle valve (which controls
airflow to the engine), the coolant temperature
sensor, the throttle position switch, idle
stabiliser valve (which bypasses air around
the throttle plate to control idle speed) and
associated relays and fuses.
Motronic fuel injection system
The Motronic system combines the fuel
control of the L-Jetronic fuel injection system
with the control of ignition timing, idle speed
and emissions into one control unit.
The fuel injection and idle speed control
functions are similar to those used on the L-
Jetronic system described above. For more
information on the Motronic system, see
Chapter 6.
An oxygen sensor is mounted in the
exhaust system on later models with a
catalytic converter. This sensor continually
reads the oxygen content of the exhaust gas.
The information is used by the ECU to adjust
the duration of injection, making it possible to
adjust the fuel mixture for optimum converter
efficiency and minimum emissions.
15 Fuel injection system-
check
2
Warning: Fuel is extremely
flammable, so take extra
precautions when you work on
any part of the fuel system. Don’t
smoke, or allow open flames or bare light
bulbs, near the work area. Don’t work in a
garage where a natural gas-type appliance
(such as a water heater or clothes dryer)
with a pilot light is present. If you spill any
fuel on your skin, rinse it off immediately
with soap and water. When you perform
any kind of work on the fuel system, wear
safety glasses, and have a fire
extinguisher on hand.
1Check the earth wire connections. Check
all wiring harness connectors that are related
to the system. Loose connectors and poor
earths can cause many problems that
resemble more serious malfunctions.
2Make sure the battery is fully charged, as
the control unit and sensors depend on an
accurate supply voltage in order to properly
meter the fuel.
3Check the air filter element - a dirty or
partially-blocked filter will severely impede
performance and economy (see Chapter 1).
4If a blown fuse is found, renew it and see if
it blows again. If it does, search for an earthed
wire in the harness related to the system.
5Check the air intake duct from the airflow
meter to the intake manifold for leaks. Intake
air leaks can cause a variety of problems. Also
check the condition of the vacuum hoses
connected to the intake manifold.
6Remove the air intake duct from the throttle
body, and check for dirt, carbon and other
residue build-up. If it’s dirty, clean it with
carburettor cleaner and a toothbrush.
7With the engine running, place a
screwdriver or a stethoscope against each
injector, one at a time, and listen for a clicking
sound, indicating operation (see illustration).
4•14 Fuel and exhaust systems
15.7 Use a stethoscope or screwdriver to
determine if the injectors are working
properly - they should make a steady
clicking sound that rises and falls with
engine speed changes

8Check the fuel system pressure (see
Section 3).
9If these checks do not locate the problem,
take the vehicle to a BMW dealer, who will be
able to read the fault codes stored in the ECU,
using special equipment.
16 Airflow meter- check,
removal and refitting
2
Check (L-Jetronic systems)
1Remove the duct from the intake end of the
airflow meter. Carefully open and close the
sensor flap (see illustration), and check for
binding. The flap can bend during a backfire,
and cause incorrect resistance readings. The
flap will bind and stick in a partially-open
position, causing the engine to run rich, and
stall when it returns to idle.
2Disconnect the electrical connector from
the airflow meter.
3Using an ohmmeter, check the resistancebetween terminals 7 and 8 (see illustration).
The resistance should increase steadily
(without any “flat spots”) as the sensor flap is
slowly moved from the fully-closed position to
the fully-open position.
4Also, check the intake air temperature
sensor (inside the airflow meter). Using an
ohmmeter, probe terminals 8 and 9 (see
illustration 16.3)and check for the proper
resistance. The resistance should be 2200 to
2700 ohms at 20º C.
5If the resistance readings are correct, check
the wiring harness (see Chapter 12). Plug in
the connector to the airflow meter. Ensure
that the ignition is switched off. Disconnect
the electrical connector from the ECU (located
under the right-hand side of the facia) and
probe terminals 7 and 8 (see illustration)with
an ohmmeter. Carefully move the door of the
airflow meter, and observe the change in
resistance as it moves from closed to fully-
open. The test results should be the same as
paragraph 3. If there are any differences in the
test results, there may be a shorted-out or
broken wire in the harness.
Check (Motronic systems)
6Ensure that the ignition is switched off.Remove the ECU access cover (see Chap-
ter 6) and disconnect the harness connector
(see illustration).
7Using an ohmmeter, probe the designated
terminals of the ECU electrical connector (see
illustrations)and check for the proper
change in resistance while moving the sensor
flap. On early Motronic systems, probe
terminals 7 and 9. On later Motronic systems,
probe terminals 7 and 12. The resistance
should increase steadily (without any “flat
spots”) as the sensor flap is slowly moved
from the fully-closed position to the fully-open
position. Note: Early Motronic systems are
distinguishable by the 35-pin ECU electrical
connector; later Motronic systems use a 55-
pin connector.
8If the resistance readings are incorrect,
check the wiring harness.
Removal and refitting (all
systems)
9Disconnect the electrical connector from
the airflow meter.
10Remove the air cleaner assembly (see
Section 8).
11Remove the nuts (see illustrations), and
lift the airflow meter from the engine
compartment or from the air cleaner
assembly.
12Refitting is the reverse of removal.
Fuel and exhaust systems 4•15
16.5 The ECU is located under the right-
hand side of the facia. Unplug the
electrical connector, and check the
resistance between terminals 7 and 8 as in
paragraph 3. The test results should be the
same.
16.3 Connect an ohmmeter to terminals 7
and 8 of the airflow meter, and check for a
smooth change in resistance as the vane
door of the airflow meter is slowly opened
and closed16.1 Check for binding of the flap in the
airflow meter as it nears closing position
or wide-open position. Any hesitation or
binding will cause erratic idle conditions,
rich fuel mixture or poor acceleration and
throttle response (airflow meter removed
for clarity)
16.7b Unplug the connector, connect the
ohmmeter probes to terminals 7 and 9
(early Motronic systems) and check for a
smooth change in resistance as the door
on the airflow meter is slowly opened and
closed16.7a Connect the ohmmeter probes to
terminals 7 and 12 (later Motronic systems)
of the ECU connector and check for a
smooth change in resistance as the door
on the airflow meter is slowly opened and
closed16.6 Remove the under-facia panel to gain
access to the ECU on Motronic systems
(left-hand-drive model shown)
4

17 Throttle body- check,
removal and refitting
2
Check
1Detach the air intake duct from the throttle
body (see Section 8) and move the duct out of
the way.
2Have an assistant depress the throttle
pedal while you watch the throttle valve.
Check that the throttle valve moves smoothly
when the throttle is moved from closed (idle
position) to fully-open (wide-open throttle).
3If the throttle valve is not working properly,
renew the throttle body unit.
Warning: Wait until the engine is
completely cool before beginning
this procedure.
Caution: If the radio in your
vehicle is equipped with an anti-
theft system, make sure you
have the correct activation code
before disconnecting the battery. Refer to
the information on page 0-7 at the front of
this manual before detaching the cable.
Note: If, after connecting the battery, the
wrong language appears on the instrument
panel display, refer to page 0-7 for the
language resetting procedure.
Removal and refitting
4Detach the battery negative cable.
5Detach the air intake duct from the throttle
body, and place to one side.
6Detach the accelerator cable from the
throttle body (see Section 9).
7Detach the cruise control cable, if applicable.
8Clearly label all electrical connectors
(throttle position sensor, cold start injector,
idle air stabiliser, etc), then unplug them.
9Clearly label all vacuum hoses, then detach
them.
10Unscrew the radiator or expansion tank
cap to relieve any residual pressure in the
cooling system, then refit it. Clamp shut the
coolant hoses, then loosen the hose clamps
and detach the hoses. Be prepared for some
coolant leakage.11Remove the throttle body mounting nuts
(upper) and bolts (lower), and detach the
throttle body from the air intake plenum (see
illustration).
12Cover the air intake plenum opening with
a clean cloth, to prevent dust or dirt from
entering while the throttle body is removed.
13Refitting is the reverse of removal. Be sure
to tighten the throttle body mounting nuts to
the torque listed in this Chapter’s Specifica-
tions, and adjust the throttle cable (see
Section 9) on completion.
18 Fuel pressure regulator-
check and renewal
3
Warning: Fuel is extremely
flammable, so take extra
precautions when you work on
any part of the fuel system. Don’t
smoke, or allow open flames or bare light
bulbs, near the work area. Don’t work in a
garage where a natural gas-type appliance
(such as a water heater or clothes dryer)
with a pilot light is present. If you spill any
fuel on your skin, rinse it off immediately
with soap and water. When you perform
any kind of work on the fuel system, wear
safety glasses, and have a fire
extinguisher on hand.
Caution: If the radio in your
vehicle is equipped with an anti-
theft system, make sure you
have the correct activation code
before disconnecting the battery. Refer to
the information on page 0-7 at the front of
this manual before detaching the cable.
Note: If, after connecting the battery, the
wrong language appears on the instrument
panel display, refer to page 0-7 for the
language resetting procedure.
Check
1Depressurise the fuel system (see Sec-
tion 2).
2Detach the battery negative cable.
3Disconnect the fuel line and connect a fuel
pressure gauge (see Section 3). Reconnect
the battery.4Pressurise the fuel system (refit the fuel
pump fuse and switch on the ignition), and
check for leakage around the gauge
connections.
5Connect a vacuum pump to the fuel
pressure regulator (see illustration).
6Run the fuel pump (see Section 3). Read the
fuel pressure gauge with vacuum applied to
the pressure regulator, and also with no
vacuum applied. The fuel pressure should
decrease as vacuum increases.
7Stop the fuel pump and reconnect the
vacuum hose to the regulator. Start the engine
and check the fuel system pressure at idle,
comparing your reading with the value listed
in this Chapter’s Specifications. Disconnect
the vacuum hose and watch the gauge - the
pressure should jump up to maximum as soon
as the hose is disconnected.
8If the fuel pressure is low, pinch the fuel
return line shut and watch the gauge. If the
pressure doesn’t rise, the fuel pump is
defective, or there is a restriction in the fuel
feed line. If the pressure now rises sharply,
renew the pressure regulator.
9If the indicated fuel pressure is too high,
stop the engine, disconnect the fuel return line
and blow through it to check for a blockage. If
there is no blockage, renew the fuel pressure
regulator.
10If the pressure doesn’t fluctuate as
described in paragraph 7, connect a vacuum
4•16 Fuel and exhaust systems
18.5 Carefully watch the fuel pressure
gauge as vacuum is applied (fuel pressure
should decrease as vacuum increases)
17.11 Remove the nuts (arrowed) and lift
the throttle body from the intake manifold
(the two lower bolts are hidden from view)16.11b Remove the nuts (arrowed) from
the air cleaner housing, and detach the
airflow meter16.11a Push the tab and remove the air
duct from inside the air cleaner assembly

gauge to the pressure regulator vacuum hose,
and check for vacuum (engine idling).
11If there is vacuum present, renew the fuel
pressure regulator.
12If there isn’t any reading on the gauge,
check the hose and its port for a leak or a
restriction.
Renewal
13Depressurise the fuel system (see Sec-
tion 2).
14Detach the battery negative cable.
Caution: If the radio in your
vehicle is equipped with an anti-
theft system, make sure you
have the correct activation code
before disconnecting the battery. Refer to
the information on page 0-7 at the front of
this manual before detaching the cable.
Note: If, after connecting the battery, the
wrong language appears on the instrument
panel display, refer to page 0-7 for the
language resetting procedure.
15Detach the vacuum hose and fuel return
hose from the pressure regulator, then
unscrew the mounting bolts (see illustration).
16Remove the pressure regulator.
17Refitting is the reverse of removal. Be sure
to use a new O-ring. Coat the O-ring with a
light film of engine oil prior to refitting.
18Check for fuel leaks after refitting the
pressure regulator.
19 Cold start injector and
thermotime switch- check
and renewal
2
Warning: Fuel is extremely
flammable, so take extra
precautions when you work on
any part of the fuel system. Don’t
smoke, or allow open flames or bare light
bulbs, near the work area. Don’t work in a
garage where a natural gas-type appliance
(such as a water heater or clothes dryer)
with a pilot light is present. If you spill any
fuel on your skin, rinse it off immediately
with soap and water. When you performany kind of work on the fuel system, wear
safety glasses, and have a fire
extinguisher on hand.
Check
Cold start injector
1The engine coolant should be below 30ºC
for this check. Preferably, the engine should
have been switched off for several hours.
Disconnect the electrical connector from the
cold start injector (see illustration)and move
it aside, away from the work area - there will
be fuel vapour present. Remove the two
screws holding the injector to the air intake
plenum, and take the injector out. The fuel line
must be left connected. Wipe the injector
nozzle. Disable the ignition system by
detaching the coil wire from the centre
terminal of the distributor cap, and earthing it
on the engine block with a jumper wire. Run
the fuel pump for 1 minute by bridging the
appropriate relay terminals (see Section 3).
There must be no fuel dripping from the
nozzle. If there is, the injector is faulty and
must be renewed. Switch off the ignition and
remake the original fuel pump relay
connections.
2Now direct the nozzle of the injector into a
can or jar. Reconnect the electrical connector
to the injector. Have an assistant switch on
the ignition and operate the starter. The
injector should squirt a conical-shaped sprayinto the jar (see illustration). If the spray
pattern is good, the injector is working
properly. If the spray pattern is irregular, the
injector is fouled or damaged, and should be
cleaned or renewed.
3If the cold start injector does not spray any
fuel, check for a voltage signal at the electrical
connector for the cold start injector when the
starter motor is operated (see illustration). If
there is no voltage, check the thermotime
switch.
Thermotime switch
4The thermotime switch detects the
temperature of the engine, and controls the
action of the cold start injector. It is usually
located up front, near the coolant temperature
sensor. The engine coolant should be below
30ºC for this check. Preferably, the engine
should have been switched off for several
hours. Disable the ignition system by detaching
the coil wire from the centre terminal of the
distributor cap, and earthing it on the engine
block with a jumper wire. Pull back the rubber
boot from the thermotime switch (see
illustration)and probe the black/yellow wire
connector terminal with a voltmeter.
5Have an assistant switch on the ignition and
operate the starter. The voltmeter should
register a voltage signal the moment the
starter engages. This signal should last
approximately 6 to 10 seconds, depending on
the temperature of the engine.
Fuel and exhaust systems 4•17
19.2 Watch for a steady, conical-shaped
spray of fuel when the starter motor is
operated19.1 Cold start injector electrical
connector (arrowed) on the M10 engine.
Most cold start injectors are mounted in
the intake manifold18.15 Remove the two bolts (arrowed) and
remove the fuel pressure regulator from
the fuel rail
19.4 Check for a voltage signal on the
black/yellow wire of the thermotime switch
when the ignition is on19.3 Check for a voltage signal (about
12 volts) at the cold start injector connector
when the starter motor is operated
4