1991 BMW 3 SERIES warning light

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

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

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

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

6If the voltage is correct, unplug the
electrical connector and, using an ohmmeter,
check for continuity between the terminals of
the thermotime switch (see illustration).
Continuity should exist.
7Reconnect the coil lead, start the engine
and warm it up above 41ºC. When the engine
is warm, there should be no continuity
between the terminals. If there is, the switch is
faulty and must be renewed. Note: On 5-
Series models, there are several types of
thermotime switch. Each one is stamped with
an opening temperature and maximum
duration.
Renewal
Cold start injector
8Depressurise the fuel system (see Sec-
tion 2).
9Disconnect the electrical connector from
the cold start injector.
10Where applicable, using a ring spanner or
deep socket, remove the fuel line fitting
connected to the cold start injector. On other
models, simply loosen the hose clamp and
detach the hose from the injector.
11Remove the cold start injector securing
bolts, and remove the injector.
12Refitting is the reverse of removal. Clean
the mating surfaces, and use a new gasket.
Thermotime switch
Warning: Wait until the engine is
completely cool before beginning
this procedure. Also, remove the
cap from the expansion tank or
radiator to relieve any residual pressure in
the cooling system.
13Prepare the new thermotime switch for
fitting by applying a light coat of thread
sealant to the threads.
14Disconnect the electrical connector from
the old thermotime switch.
15Using a deep socket, or a ring spanner,
unscrew the switch. Once the switch is
removed coolant will start to leak out, so
insert the new switch as quickly as possible.
Tighten the switch securely, and plug in the
electrical connector.
20 Fuel injectors-
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 perform
any kind of work on the fuel system, wear
safety glasses, and have a fire
extinguisher on hand.
Check
In-vehicle check
1Using a mechanic’s stethoscope (available
at most car accessory shops), check for a
clicking sound at each of the injectors while
the engine is idling (see illustration 15.7).
2The injectors should make a steady clicking
sound if they are operating properly.
3Increase the engine speed above 3500 rpm.
The frequency of the clicking sound should
rise with engine speed.
4If an injector isn’t functioning (not clicking),
purchase a special injector test light (a car
accessory shop or fuel injection specialist
may be able to help) and connect it to the
injector electrical connector. Start the engine
and make sure the light flashes. If it does, the
injector is receiving the proper voltage, so the
injector itself must be faulty.
5Unplug each injector connector, and checkthe resistance of the injector (see
illustration). Check your readings with the
values listed in this Chapter’s Specifications.
Renew any that do not give the correct
resistance reading.
Volume test
6Because a special injection checker is
required to test injector volume, this
procedure is beyond the scope of the home
mechanic. Have the injector volume test
performed by a BMW dealer or other
specialist.
Renewal
7Unplug the main electrical connector for the
fuel injector wiring harness. Remove the
intake manifold (see Chapter 2A).
8Detach the fuel hoses from the fuel rail, and
remove the fuel rail mounting bolts (see
illustration).
9Lift the fuel rail/injector assembly from the
intake manifold.
10Unplug the electrical connectors from the
fuel injectors. Detach the injectors from the
fuel rail.
11Refitting is the reverse of removal. Be sure
to renew all O-rings. Coat the O-rings with a
light film of engine oil to prevent damage
during refitting. Pressurise the fuel system
(refit the fuel pump fuse and switch on the
ignition) and check for leaks before starting
the engine.
21 Idle air stabiliser valve-
check, adjustment and
renewal
4
1The idle air stabiliser system works to
maintain engine idle speed within a 200 rpm
range, regardless of varying engine loads at
idle. An electrically-operated valve allows a
small amount of air to bypass the throttle
plate, to raise the idle speed whenever the idle
speed drops below approximately 750 rpm. If
the idle speed rises above approximately
950 rpm, the idle air stabiliser valve closes
and stops extra air from bypassing the throttle
plate, reducing the idle speed.
4•18 Fuel and exhaust systems
20.8 Remove the bolts (arrowed) and
separate the fuel rail and injectors from
the intake manifold20.5 Check the resistance of each of the
fuel injectors19.6 Check the resistance of the
thermotime switch with the engine coolant
temperature below 30º C. There should be
continuity
If you don’t have a
mechanic’s stethoscope, a
screwdriver can be used to
check for a clicking sound at
the injectors. Place the tip of the
screwdriver against the injector, and
press your ear against the handle.

7 Ignition timing (TCI system)-
check and adjustment
4
Warning: Keep hands, equipment
and wires well clear of the
viscous cooling fan during
adjustment of the ignition timing.
Note:This Section describes the procedure
for checking and adjusting the ignition timing
on engines fitted with the TCI system. On
engines fitted with the Motronic engine
management system, the ignition timing is
controlled by the electronic control unit, and
no adjustment is possible. The timing can be
checked using the following procedure, but no
ignition timing values were available at the
time of writing. If the timing is thought to be
incorrect, refer to a BMW dealer.
1Some special tools are required for this
procedure (see illustration). The engine must
be at normal operating temperature, and the
air conditioning (where fitted) must be
switched off. Make sure the idle speed is
correct.
2Apply the handbrake, and chock the wheels
to prevent movement of the vehicle. The
transmission must be in neutral (manual) or
Park (automatic).
3The timing marks are located on the engine
flywheel (viewed through the timing checkhole in the bellhousing) and/or on the vibration
damper on the front of the engine.
4Where applicable, disconnect the vacuum
hose from the distributor vacuum advance
unit.
5Connect a tachometer and timing light
according to the equipment manufacturer’s
instructions (an inductive pick-up timing light
is preferred). Generally, the power leads for
the timing light are attached to the battery
terminals, and the pick-up lead is attached to
the No 1 spark plug HT lead. The No 1 spark
plug is the one at the front of the engine.
Caution: If an inductive pick-up
timing light isn’t available, don’t
puncture the spark plug HT lead
to attach the timing light pick-up
lead. Instead, use an adapter between the
spark plug and HT lead. If the insulation on
the HT lead is damaged, the secondary
voltage will jump to earth at the damaged
point, and the engine will misfire.
Note:On some models, a TDC transmitter is
fitted for checking the ignition system.
However, a special BMW tester must be
connected to the diagnostic socket to use it,
so unless the special tester is available, a
conventional timing light should be used. The
ignition timing mark may be on the vibration
damper, but if not, normally the TDC mark will
be. If the timing light is of the adjustable delay
type, then the ignition timing may be
determined by zeroing the adjustment, then
turning the adjustment until the TDC marks are
aligned, and then reading off the amount of
advance from the timing light. If a standard
timing light is being used, make a mark on the
vibration damper in accordance with the
specified advance, using the following formula
to calculate the distance from the TDC mark
to the timing mark:
Distance = 2Pr x advance
360
where P = 3.142
r = radius of vibration damper
advance = specified advance
BTDC in degrees
6With the ignition off, loosen the distributor
clamp nut just enough to allow the distributor
to pivot without any slipping.7Make sure the timing light wires are routed
away from the drivebelts and fan, then start
the engine.
8Raise the engine rpm to the specified
speed, and then point the flashing timing light
at the timing marks - be very careful of moving
engine components.
9The mark on the flywheel or vibration
damper will appear stationary. If it’s aligned
with the specified point on the bellhousing or
engine front cover, the ignition timing is
correct (see illustrations).
10If the marks aren’t aligned, adjustment is
required. Turn the distributor very slowly until
the marks are aligned, taking care not to
touch the HT leads.
11Tighten the nut on the distributor clamp,
and recheck the timing.
12Switch off the engine, and remove the
timing light and tachometer. Reconnect the
vacuum hose where applicable.
8 Distributor-
removal and refitting
4
TCI system
Removal
1After carefully marking them for position,
remove the coil HT lead and spark plug HT
leads from the distributor cap (see Chapter 1).
2Remove No 1 spark plug (the one nearest
you when you are standing in front of the
engine).
3Manually rotate the engine to Top Dead
Centre (TDC) on the compression stroke for
No 1 piston (see Chapter 2A)
4Carefully mark the vacuum hoses, if more
than one is present on your distributor.
5Disconnect the vacuum hose(s).
6Disconnect the primary circuit wires from
the distributor.
7Mark the relationship of the rotor tip to the
distributor housing (see illustration). Also
mark the relationship of the distributor
housing to the engine.
5•4 Engine electrical systems
7.1 Tools for checking and adjusting the
ignition timing
1Vacuum plugs- Vacuum hoses will, in
most cases, have to be disconnected and
plugged. Moulded plugs in various shapes
and sizes can be used for this, if wished
2Inductive pick-up timing light- Flashes a
bright, concentrated beam of light when
No 1 spark plug fires. Connect the leads
according to the instructions supplied with
the light
3Distributor spanner - On some models,
the hold-down bolt for the distributor is
difficult to reach and turn with conventional
spanners or sockets. A special spanner like
this must be used
7.9a Flywheel “OT” timing mark 7.9b Flywheel “OZ” timing mark

8Use a digital voltmeter for the following
tests:
a) On Bosch systems, connect the positive
probe to connector terminal 5, and the
negative probe to terminal 6 (see
illustration).
b) On Siemens/Telefunken systems, connect
the positive probe to terminal (+) of the
smaller connector, and the negative
probe to terminal (-).
9Have an assistant crank the engine over,
and check that there is 1 to 2 volts A/C
present. If there is no voltage, check the
wiring harness between the impulse generator
(in the distributor) and the control unit. If the
harness is OK, check the impulse generator
resistance.
Warning: Do not crank the
engine over for an excessive
length of time. If necessary,
disconnect the cold start injector
electrical connector (see Chapter 4) to
stop the flow of fuel into the engine.
10To check the resistance in the impulse
generator, proceed as described for your
system below:
a) On Bosch units, measure the resistance
between connector terminals 5 and 6
(see illustration 10.8). The reading
should be 1000 to 1200 ohms.
b) On Siemens/Telefunken units, measure
the resistance between the terminals of
the smaller connector. The reading should
be 1000 to 1200 ohms.
11If the resistance readings are incorrect,
renew the impulse generator. If the resistance
readings for the impulse generator are correct
and the control unit voltages (supply voltage
[paragraphs 1 to 6] and signal voltage
[paragraphs 7 to 9]) are incorrect, renew the
control unit.
Renewal
Ignition control unit
12Make sure the ignition is switched off.
13Disconnect the electrical connector(s)
from the control unit.
14Remove the mounting screws from the
control unit, and lift it from the engine
compartment.15Refitting is the reverse of removal. Note:
On Bosch control units, a special dielectric
grease is used between the heat sink and the
back of the control unit. In the event the two
are separated (renewal or testing) the old
grease must be removed, and the heat sink
cleaned off using 180-grit sandpaper. Apply
Curil K2 (Bosch part number 81 22 9 243). A
silicon dielectric compound can be used as a
substitute. This treatment is very important for
the long life of these expensive ignition parts.
Impulse generator
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.
16Disconnect the battery negative cable.
17Remove the distributor from the engine
(see Section 8).
18Using a pair of circlip pliers, remove the
circlip retaining the trigger wheel (see
illustration).
19Use two flat-bladed screwdrivers
positioned at opposite sides of the trigger
wheel, and carefully prise it up (see
illustration). Note: Push the screwdrivers in
as far as possible without bending the trigger
wheel. Prise only on the strongest, centre
portion of the trigger wheel. In the event the
trigger wheel is bent, it must be replaced with
a new one. Note:Be sure not to lose the roll
pin when lifting out the trigger wheel.
20Remove the mounting screws from the
impulse generator electrical connector, the
vacuum diaphragm and the baseplate.
21Remove the two screws from the vacuum
advance unit, and separate it from the
distributor by moving the assembly down
while unhooking it from the baseplate pin.
22Use circlip pliers to remove the circlip that
retains the impulse generator and the
baseplate assembly.
23Carefully remove the impulse generator
and the baseplate assembly as a single unit.24Remove the three screws, and separate
the baseplate assembly from the impulse
generator.
25Refitting is the reverse of removal. Note:
Be sure to position the insulating ring between
the generator coil and the baseplate. It must
be centred before tightening the mounting
screws. Also, it will be necessary to
check/adjust the air gap if the trigger wheel
has been removed, or tampered with to the
point that the clearance is incorrect (see
Section 11).
11 Air gap (TCI system)-
check and adjustment
2
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.
1Disconnect the battery negative cable.
2Insert a brass feeler gauge between the
trigger wheel tab and the impulse generator
(see illustration). Slide the feeler gauge up
Engine electrical systems 5•7
10.19 Carefully prise the trigger wheel off
the distributor shaft10.18 Use circlip pliers and remove the
circlip from the distributor shaft10.8 Back-probe the ignition control unit
connector, and check for signal voltage on
terminals 5 and 6 (Bosch system shown). It
is very helpful to use angled probes
11.2 Use a brass feeler gauge to check
the air gap (be sure the gauge rubs lightly
against the trigger wheel as well as the
locating pin for the correct adjustment)
5