1988 BMW 3 SERIES Wire

M20 engine
9Remove the distributor cap and HT leads,
ignition rotor and dust shield (see Chapter 1).
10Where applicable, remove the timing
sensor (see Chapter 5).
11Remove the timing belt upper cover (see
Chapter 2A).
12Loosen all three water pump mounting
bolts. Remove the top and right-hand side
bolts, but DON’T remove the lower bolt (see
illustration).
13Rotate the pump downwards, and remove
the drivebelt tensioner spring and pin.
14 Remove the final water pump bolt, and
remove the pump.
Caution: Leave the tensioner bolt
tight. Be careful to not move the
camshaft gear, as damage can
occur if the valves are moved.
M30 engine
15Remove the engine lifting bracket.
16Remove the bolts that mount the water
pump to the engine block.
17Remove the water pump, and recover the
gasket.
M40 engine
18Unscrew the mounting bolts and remove
the water pump. If the pump is tight in the
cylinder head, insert two bolts in the special
lugs at the top and bottom of the pump, and
tighten them evenly to press the pump out of
the head (see illustrations).
Refitting
19Clean the bolt threads and the threaded
holes in the engine to remove corrosion and
sealant.
20Compare the new pump to the old one, to
make sure they’re identical.
21Remove all traces of old gasket material
from the engine with a gasket scraper.
22Clean the water pump mating surfaces.
23On the M40 engine, locate a new O-ring
on the pump (see illustration).
24Locate the gasket on the pump, and offer
the pump up to the engine (see illustration).
Slip a couple of bolts through the pump
mounting holes to hold the gasket in place.
25Carefully attach the pump and gasket to
the engine, threading the bolts into the holes
finger-tight.Note:On the M20 engine, refit the
lower bolt finger-tight, then rotate the water
pump into position with the drivebelt tensioner
spring and pin in position.
26Refit the remaining bolts (if they also hold
an accessory bracket in place, be sure to
reposition the bracket at this time). Tighten
them to the torque listed in this Chapter’s
Specifications, in quarter-turn increments.
Don’t overtighten them, or the pump may be
distorted.
27Refit all parts removed for access to the
pump.
28Refill the cooling system and check the
drivebelt tension (see Chapter 1). Run the
engine and check for leaks.8 Coolant temperature sender
unit- check and renewal
2
Warning: Wait until the engine is
completely cool before beginning
this procedure.
1The coolant temperature indicator system
is composed of a temperature gauge
mounted in the instrument panel, and a
coolant temperature sender unit that’s
normally mounted on the thermostat housing
(see illustration 3.11). Some vehicles have
more than one sender unit, but only one is
used for the temperature gauge. On the M40
engine, the sender unit is mounted on the left-
hand side of the cylinder head, towards the
rear.
2If the gauge reading is suspect, first check
the coolant level in the system. Make sure the
wiring between the gauge and the sending
unit is secure, and that all fuses are intact. (If
the fuel gauge reading is suspect as well, the
problem is almost certainly in the instrument
panel or its wiring.)
3Before testing the circuit, refer to the
relevant wiring diagrams (see Chapter 12).
Where the sender unit simply earths out the
circuit, test by earthing the wire connected to
the sending unit while the ignition is on (but
without the engine running, for safety). If the
gauge now deflects to the end of the scale,
renew the sender unit. If the gauge does not
respond satisfactorily, the gauge, or the wiring
to the gauge, is faulty. Where the sender unit
has two terminals, test the circuit by checking
the resistance of the unit. No figures were
available at the time of writing, but typically
readings of several hundred or several
thousand ohms (depending on temperature)
would be expected. A reading of zero (short-
circuit) or infinity (open-circuit) would indicate
a faulty sender unit.
Caution: Do not earth the wire
for more than a second or two, or
damage to the gauge could
occur.
3•6 Cooling, heating and air conditioning systems
7.24 New outer gasket on the M40 engine
water pump7.23 Fit a new O-ring on the M40 engine
water pump
7.18b . . . and remove the water pump
(M40 engine)7.18a With the water pump mounting bolts
removed, screw two bolts into the special
lugs (one top and one bottom) . . .7.12 Water pump bolt locations on the
M20 engine

4If a new sender unit is to be fitted, make
sure the engine is completely cool. There will
be some coolant loss when the unit is
unscrewed, so be prepared to catch it, or
have the new unit ready to fit immediately the
old one is removed. Disconnect the wiring,
then unscrew the old unit from the engine,
and fit the new one. Use sealant on the
threads. Reconnect the wiring, and check the
coolant level on completion.
9 Heater and air conditioning
blower motor- removal,
testing and refitting
1
Removal
Note: The 3-Series models covered by this
manual have always used a single blower
motor for ventilation, heating and air
conditioning. “Old-shape” (E28) 5-Series
models use two separate blower motors: one
for ventilation and heating, and another for air
conditioning. “New-shape” (E34) 5-Series
models have a single blower motor, like the 3-
Series. The removal and refitting of the single
blower motor, and the old-shape 5-Series
vent/heat motor, is described below. The
removal and refitting of the old-shape 5-Series
air conditioning blower motor is described in
Section 14 of this Chapter.
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.
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.
1Disconnect the battery negative cable.
2The blower motor is located behind the
bulkhead, under an access panel. Remove the
panel securing screws (see illustrations).
3Disconnect or cut the plastic ties holding
the wiring harness to the panel, and move the
wiring out of the way.
4Remove the panel.
5Unclip the blower housing retaining clip,
and the clip securing the blower motor (see
illustrations).6Disconnect the wiring and remove the
blower motor (see illustration).
Testing
7You can test the blower motor by applying
battery voltage to the blower motor’s
terminals with fused jumper wires (be sure the
fan blades won’t hit anything when they
rotate). If the blower motor spins the fan
blades rapidly (this test simulates high-speed
operation), the blower motor is OK. If the
blower motor does not operate, or operates
slowly or noisily, renew it.
Note: If the fan blade assemblies need to be
removed, mark their relationship to the shaft.
The assemblies are balanced during
production, and excessive noise or shortened
bearing life could result if they are not refitted
in exactly the same position in relation to the
shaft.
Refitting
8Refitting is the reverse of removal. Note:
The blower motor may have to be rotated to
allow the retaining clip to line up correctly.
10 Heater and air conditioner
control assembly- removal
and refitting
1
Removal
1Disconnect 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.
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-Series models
2Remove the centre console and side trim
pieces.
3Remove the radio (see Chapter 12), then
pull the knobs off the heater/air conditioning
control levers.
4Remove the heater trim panel to gain
access to the control cables.
5Disconnect the cables, marking them for
accurate refitting.
6Disconnect the electrical connector.
7Remove the lever assembly.
8Each lever assembly can be removed
separately.
5-Series models
9Remove the centre console (see Chap-
ter 11).
10Remove the radio (see Chapter 12), then
pull the knobs off the heater/air conditioning
control levers.
11Remove the trim bezel, and pull the
control unit from the dash. This will allow you
to disconnect the control cables from the
lever assembly.
Cooling, heating and air conditioning systems 3•7
9.5a Unclip the retaining strap to remove
the blower housing . . .
9.2b . . . a fastener from the top secure the
panel9.2a To get to the heater blower motor,
the access panel must be removed - a
fastener from the front and . . .
9.6 Lift out the assembly, and disconnect
the electrical connection from the blower
motor9.5b . . . and unclip the centre strap that
secures the blower motor assembly
3

Note 3:The following checks assume the fuel
filter is in good condition. If you doubt the
condition of your fuel filter, renew it (see
Chapter 1).
Note 4:In order to get accurate test results, it
is recommended that the fuel pressure be
checked from both the main fuel pump and
transfer pump where applicable.
Fuel pump/transfer pump operational
check
6Bridge the connector terminals that
correspond to the fuel pump relay pins 30 and
87b (L-Jetronic systems) or 30 and 87
(Motronic systems) with a suitable jumper wire
(see illustrations).
7Have an assistant switch the ignition on
while you listen at the fuel tank. You should
hear a whirring sound for a couple of seconds.
Note:This test applies to the transfer pump
also. If there is no whirring sound, there is a
problem in the fuel pump circuit. Check the
fuel pump main fuse and relay first (see
Chapter 12). If the main relay is OK, test the
fuel pump relay.
Fuel system pressure check8Depressurise the fuel system (see Section 2).
9Detach 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 codebefore 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.
10Detach the fuel feed line from the fuel rail
on L-Jetronic (see illustration)and early
Motronic systems, or from the fuel filter to the
main fuel line on later Motronic systems.
11Using a tee-piece (three-way fitting), a
short section of high-pressure fuel hose and
clamps, attach a fuel pressure gauge without
disturbing normal fuel flow (see illustration).
Warning: Do not use a plastic tee
fitting for this test. It won’t be
able to withstand the fuel system
pressure.
12Reconnect the battery.
13Bridge the terminals of the fuel pump
relay using a jumper wire.
14Turn the ignition switch on.
15Note the fuel pressure, and compare it
with the pressure listed in this Chapter’s
Specifications.
16If the system fuel pressure is less than
specified:
a) Check the system for fuel leaks. Repair
any leaks found, and recheck the fuel
pressure.b) If there are no leaks, fit a new fuel filter
and recheck the fuel pressure.
c) If the pressure is still low, check the fuel
pump pressure (see below) and the fuel
pressure regulator (see Section 18).
17If the pressure is higher than specified,
check the fuel return line for an obstruction. If
the line is not obstructed, renew the fuel
pressure regulator.
18Turn the ignition off, wait five minutes and
look at the gauge. Compare the reading with
the system hold pressure listed in this
Chapter’s Specifications. If the hold pressure
is less than specified:
a) Check the system for fuel leaks. Repair
any leaks found, and recheck the fuel
pressure.
b) Check the fuel pump pressure (see
below).
c) Check the fuel pressure regulator (see
Section 18).
d) Check the injectors (see Section 20).
Fuel pump pressure check
Warning: For this test, a fuel
pressure gauge with a bleed
valve will be needed, in order to
relieve the high fuel pressure
safely. After the test is completed, the
normal procedure for depressurising will
not work, because the gauge is connected
directly to the fuel pump.
4•4 Fuel and exhaust systems
3.10 Disconnect the fuel feed line
(arrowed) from the fuel rail (L-Jetronic
system shown) . . .3.6d . . . then, use a jumper wire to bridge
the terminals on the connector that
correspond to fuel pump relay pins 30 and
87
3.6c On all 1989 and later models, remove
the four bolts and the protective cover to
gain access to the fuel pump relay and
ECU . . .3.6b On Motronic systems, use a jumper
wire to bridge the terminals on the
connector that correspond to the fuel
pump relay pins 30 and 873.6a On L-Jetronic systems, use a jumper
wire to bridge the terminals on the
connector that correspond to the fuel
pump relay pins 30 and 87b
3.11 . . . and connect the gauge between
the fuel feed line and the fuel rail using a
tee-piece fitting

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

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

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