1986 BMW 3 SERIES sensor

reading should be between 400 and 500 mA.
Adjust the valve if the current reading is not as
specified. Note: The idle air stabiliser current
will fluctuate between 400 and 1100 mA if the
engine is too cold, if the coolant temperature
sensor is faulty, if there is an engine vacuum
leak, or if electrical accessories are on.
25If there is no current reading, have the idle
speed control unit (under the facia) checked
by a BMW dealer or other specialist.
26On three-wire valves, check for voltage at
the electrical connector. With the ignition on,
there should be battery voltage present at the
centre terminal (see illustration). There
should be about 10 volts between the centre
terminal and each of the outer terminals.
27If there is no voltage reading, have the idle
speed control unit (early models) or the ECU
(later models) checked by a dealer service
department or other specialist.
Adjustment (early models only)
28With the ignition switched off, connect a
tachometer in accordance with the equipment
manufacturer’s instructions.
29Make sure the ignition timing is correct
(see Chapter 5).
30Connect an ammeter to the valve as
described in paragraph 13.
31With the engine running, the current draw
should be 450 to 470 mA at 700 to 750 rpm.
32If the control current is not correct, turn
the adjusting screw until it is within the
specified range. Note: Turn the idle air bypass
screw clockwise to increase the current, or
anti-clockwise to decrease the current.
Renewal
33Remove the electrical connector and the
bracket from the idle air stabiliser valve.
Remove the valve, disconnecting the hoses.
34Refitting is the reverse of removal.
22 Exhaust system servicing-
general information
Warning: Inspect or repair
exhaust system components only
when the system is completely
cool. When working under the
vehicle, make sure it is securely
supported.
Silencer and pipes
1The exhaust system consists of the exhaust
manifold, catalytic converter, silencers, and all
connecting pipes, brackets, mountings (see
illustration)and clamps. The exhaust system
is attached to the body with brackets and
rubber mountings. If any of the parts are
improperly fitted, excessive noise and
vibration may be transmitted to the body.
2Inspect the exhaust system regularly. Look
for any damaged or bent parts, open seams,
holes, loose connections, excessive
corrosion, or other defects which could allow
exhaust fumes to enter the vehicle. Generally,
deteriorated exhaust system components
cannot be satisfactorily repaired; they should
be renewed.3If the exhaust system components are
extremely corroded or rusted together, it may
be necessary to cut off the old components
with a hacksaw. Be sure to wear safety
goggles to protect your eyes from metal
chips, and wear work gloves to protect your
hands.
4Here are some simple guidelines to follow
when repairing the exhaust system:
a) Work from the back to the front of the
vehicle when removing exhaust system
components.
b) Apply penetrating oil to the exhaust
system nuts and bolts to make them
easier to remove.
c) Use new gaskets, mountings and clamps
when fitting exhaust system components.
d) Apply anti-seize compound to the threads
of all exhaust system nuts and bolts
during reassembly.
e) Be sure to allow sufficient clearance
between newly-fitted parts and all points
on the underbody, to avoid overheating
the floorpan, and possibly damaging the
interior carpet and insulation. Pay
particularly close attention to the catalytic
converters and heat shields. Also, make
sure that the exhaust will not come into
contact with suspension parts, etc.
Catalytic converter
5Although the catalytic converter is an
emissions-related component, it is discussed
here because, physically, it’s an integral part
of the exhaust system. Always check the
converter whenever you raise the vehicle to
inspect or service the exhaust system.
6Raise and support the vehicle.
7Inspect the catalytic converter for cracks or
damage.
8Check the converter connections for
tightness.
9Check the insulation covers welded onto the
catalytic converter for damage or a loose fit.
Caution: If an insulation cover is
dented so that it touches the
converter housing inside,
excessive heat may be
transferred to the floor.
10Start the engine and run it at idle speed.
Check all converter connections for exhaust
gas leakage.
4•20 Fuel and exhaust systems
22.1 A typical exhaust system rubber
mounting21.26 Check for battery voltage on the
centre terminal

Fuel injection system - fault finding
L-Jetronic fuel injection system
Engine difficult to start, or fails to start (when cold)
Probable cause Corrective action
Cold start injector or thermotime switch faulty Test cold start injector and thermotime switch. Renew faulty components (see Section 19)
Fuel pump inoperative Check fuel pump fuse and fuel pump relay (see Sections 3 and 4)
Airflow meter flap (door) binding or stuck
in open position Inspect the airflow meter for damage (see Section 16)
Fuel pressure incorrect Test system pressure (see Section 3). Test fuel pressure regulator (Section 18)
Intake air leaks Inspect all vacuum lines, air ducts, and oil filler and dipstick seals
Fuel injectors clogged or not operating Check fuel injectors (see Section 20) and wiring harness
Coolant temperature sensor faulty or
wiring problem Test coolant temperature sensor (see Chapter 6, Section 4)
Throttle position sensor (TPS) incorrectly adjusted Check TPS adjustment (see Chapter 6, Section 4)
Incorrect ignition timing Check ignition timing (see Chapter 5). Check vacuum advance system
Dirt or other contaminants in fuel Check the fuel and drain the tank if necessary
Faulty ECU Have the ECU tested at a dealer service department or other specialist
Engine difficult to start, or fails to start (when warm)
Probable cause Corrective action
Cold start injector leaking or operating continuously Test cold start injector and thermotime switch (see Section 19)
Fuel pressure incorrect Test fuel pump(s). Renew if necessary (see Section 3)
Insufficient residual fuel pressure Test residual fuel pressure. Renew fuel pump or fuel accumulator as necessary
(see Section 18)
Fuel leak(s) Inspect fuel lines and fuel injectors for leaks. Correct leaks as required (see Chapter 4)
Coolant temperature sensor faulty or
wiring problem Test coolant temperature sensor (see Chapter 6, Section 4)
Vapour lock (warm weather) Check fuel pressure (see Section 3)
EVAP system faulty (where applicable) Check EVAP system (see Chapter 6, Section 6)
Incorrect ignition timing Check ignition timing (see Chapter 5). Check vacuum advance system
Faulty ECU Have the ECU tested at a dealer service department or other specialist
Idle speed control system faulty Test the idle air stabiliser valve (see Section 21)
Engine misses and hesitates under load
Probable cause Corrective action
Fuel injector clogged or faulty Test fuel injectors. Check for clogged injector lines. Renew faulty injectors (see Section 20)
Fuel pressure incorrect Test fuel system pressure (see Section 3). Test fuel pressure regulator (see Section 18)
Fuel leak(s) Inspect fuel lines and fuel injectors for leaks (see Chapter 4)
Engine maintenance Tune-up engine (see Chapter 1). Check the distributor cap, rotor, HT leads and spark
plugs, and renew any faulty components
Airflow meter flap (door) binding, or
stuck in open position Inspect the airflow meter for damage (see Section 16)
Intake air leaks Inspect all vacuum lines, air ducts and oil filler and dipstick seals
Engine has erratic idle speed
Probable cause Corrective action
Idle air stabiliser valve faulty Check the idle air stabiliser valve (see Section 21)
No power to the idle air stabiliser valve Check the idle air stabiliser relay and wiring circuit (see Chapter 12)
Vacuum advance system faulty Check vacuum advance system and electronic vacuum advance relay
Idle speed control unit faulty Have the idle speed control unit checked by a dealer
Motronic fuel injection system
Note:With this system, when faults occur, the ECU stores a fault code in its memory. These codes can only be read by a BMW dealer, as
specialised equipment is required. It may save time to have at least the initial fault diagnosis carried out by a dealer.
Lack of power
Probable cause Corrective action
Coolant temperature sensor faulty, Test coolant temperature sensor and wiring. Repair wiring or renew sensor if
or wire to sensor broken faulty (see Chapter 6)
Fuel pressure incorrect Check fuel pressure from main pump and transfer pump, as applicable (see Section 3)
Throttle plate not opening fully Check accelerator cable adjustment to make sure throttle is opening fully. Adjust cable if
necessary (see Section 9)
Fuel and exhaust systems 4•21
4

Engine difficult to start, or fails to start (when cold)
Probable cause Corrective action
Cold start injector or thermotime switch
faulty (early Motronic system only) Test cold start injector and thermotime switch. Renew faulty components (see Section 19)
Fuel pump not running Check fuel pump fuse and fuel pump relay (see Sections 2 and 3)
Airflow meter flap (door) binding, or
stuck in open position Inspect the airflow meter for damage (see Section 16)
Fuel pressure incorrect Test system pressure (see Section 3)
Intake air leaks Inspect all vacuum lines, air ducts and oil filler and dipstick seals
Fuel injectors clogged or not operating Check fuel injectors (see Section 20) and wiring harness
Coolant temperature sensor faulty or Test coolant temperature sensor (see Chapter 6, Section 4)
wiring problem
TPS (throttle position sensor) incorrectly adjusted Check TPS adjustment (see Chapter 6, Section 4)
Dirt or other contaminants in fuel Check the fuel and drain the tank if necessary
Faulty ECU Have the ECU tested at a dealer service department or other specialist
Crankshaft position signal missing Faulty position sensor or flywheel, or reference pin missing (see Chapter 5)
Engine difficult to start, or fails to start (when warm)
Probable cause Corrective action
Cold start injector leaking or operating
continuously (early Motronic system only) Test cold start injector and thermotime switch (see Section 19)
Fuel pressure incorrect Test fuel pressure (see Section 3)
Insufficient residual fuel pressure Test fuel system hold pressure (see Section 3)
Fuel leak(s) Inspect fuel lines and fuel injectors for leaks. Correct leaks as necessary
Coolant temperature sensor faulty
or wiring problem Test coolant temperature sensor (see Chapter 6, Section 4)
Vapour lock (in warm weather) Check fuel pressure (see Section 3)
EVAP system faulty Check EVAP system (see Chapter 6, Section 6)
Faulty ECU Have the ECU tested at a dealer service department or other specialist
Idle speed control system faulty Test the idle air stabiliser valve (see Section 21)
Oxygen sensor faulty (where applicable) Check the oxygen sensor (see Chapter 6, Section 4)
Engine misses and hesitates under load
Probable cause Corrective action
Fuel injector clogged Test fuel injectors. Check for clogged injector lines. Renew faulty injectors (see Section 20)
Fuel pressure incorrect Test fuel system pressure (see Section 3). Test fuel pressure regulator (see Section 18)
Fuel leak(s) Inspect fuel lines and fuel injectors for leaks (see Chapter 4)
Engine maintenance Tune-up engine (see Chapter 1). Check the distributor cap, rotor, HT leads and spark
plugs, and renew any faulty components
Airflow meter flap (door) binding, or Inspect the airflow meter for damage (see Section 16)
stuck in open position
Intake air leaks Inspect all vacuum lines, air ducts, and oil filler and dipstick seals
Throttle position sensor (TPS) incorrectly adjusted Check TPS adjustment (see Chapter 6)
Engine idles too fast
Probable cause Corrective action
Accelerator pedal, cable or throttle valve binding Check for worn or broken components, kinked cable, or other damage. Renew faulty
components
Air leaking past throttle valve Inspect throttle valve, and adjust or renew as required
Engine has erratic idle speed
Probable cause Corrective action
Idle air stabiliser valve faulty Check the idle air stabiliser valve (see Section 21)
No power to the idle air stabiliser valve Check the idle air stabiliser relay and wiring circuit (see Chapter 12)
Idle speed control unit faulty Have the idle speed control unit checked by a dealer
Poor fuel economy
Probable cause Corrective action
Cold start injector leaking
(early Motronic system only) Test and, if necessary, renew cold start injector (see Section 19)
Oxygen sensor faulty (where applicable) Test the oxygen sensor (see Chapter 6, Section 4))
Sticking handbrake/binding brakes Check the handbrake/braking system (see Chapter 9)
Tyre pressures low Check tyre pressures (Chapter 1)
4•22 Fuel and exhaust systems

5GeneralApplication
Models with carburettor or L-Jetronic fuel injection . . . . . . . . . . . . . . Transistorised Coil Ignition (TCI) system
Models with Motronic fuel injection . . . . . . . . . . . . . . . . . . . . . . . . . . Ignition functions controlled by Motronic system
Ignition coil
Primary resistance
TCI system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.82 ohms
Motronic system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.50 ohms
Secondary resistance
TCI system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8250 ohms
Motronic system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5000 to 6000 ohms
Distributor(models with TCI system)
Air gap . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.3 mm to 0.7 mm
Pick-up coil/impulse generator resistance . . . . . . . . . . . . . . . . . . . . . . . 900 to 1200 ohms
Ignition timing(models with TCI system)
(Vacuum line disconnected at distributor)
316 with M10/B18 engine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25º BTDC at 2500 rpm (2900 rpm from 9/83)
318i with M10/B18 engine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30º BTDC at 3000 rpm
320i with M20/B20 engine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23º BTDC at 5000 ±50 rpm
518 with M10/B18 engine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25º BTDC at 2900 ±50 rpm
518i with M10/B18 engine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30º BTDC at 3000 ±50 rpm
525i with M30/B25 engine (except distributor
237 302 033) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22º BTDC at 1800 ±50 rpm
525i with M30/B25 engine (distributor 237 302 033) . . . . . . . . . . . . . . . 22º BTDC at 2150 ±50 rpm
528i with M30/B28 engine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22º BTDC at 2150 ±50 rpm
Chapter 5 Engine electrical systems
Air gap (TCI system) – check and adjustment . . . . . . . . . . . . . . . . . . 11
Alternator – removal and refitting . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Alternator brushes – check and renewal . . . . . . . . . . . . . . . . . . . . . . 17
Battery – emergency jump starting . . . . . . . . . . . . . . . . . . . . . . . . . . 2
Battery – removal and refitting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Battery cables – check and renewal . . . . . . . . . . . . . . . . . . . . . . . . . 4
Battery check and maintenance . . . . . . . . . . . . . . . . See Chapter 1
Charging system – check . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Charging system – general information and precautions . . . . . . . . . 13
Distributor – removal and refitting . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Drivebelt check, adjustment and renewal . . . . . . . . . See Chapter 1
General information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Ignition coil – check and renewal . . . . . . . . . . . . . . . . . . . . . . . . . . . 9Ignition sensors (Motronic system) – check and renewal . . . . . . . . . 12
Ignition system – check . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Ignition system – general information and precautions . . . . . . . . . . 5
Ignition timing (TCI system) – check and adjustment . . . . . . . . . . . . 7
Impulse generator and ignition control unit – check and
renewal (TCI system) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Spark plug HT lead check and renewal . . . . . . . . . . . See Chapter 1
Spark plug renewal . . . . . . . . . . . . . . . . . . . . . . . . . . See Chapter 1
Starter motor – in-vehicle check . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Starter motor – removal and refitting . . . . . . . . . . . . . . . . . . . . . . . . 20
Starter solenoid – removal and refitting . . . . . . . . . . . . . . . . . . . . . . 21
Starting system – general information and precautions . . . . . . . . . . 18
Voltage regulator – renewal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
5•1
Easy,suitable for
novice with little
experienceFairly easy,suitable
for beginner with
some experienceFairly difficult,
suitable for competent
DIY mechanic
Difficult,suitable for
experienced DIY
mechanicVery difficult,
suitable for expert
DIY or professional
Degrees of difficulty
Specifications Contents

5 Ignition system- general
information and precautions
The ignition system includes the ignition
switch, the battery, the distributor, the primary
(low-voltage/low-tension or LT) and
secondary (high-voltage/high-tension or HT)
wiring circuits, the spark plugs and the spark
plug leads. Models fitted with a carburettor or
L-Jetronic fuel injection are equipped with a
Transistorised Coil Ignition (TCI) system.
Models fitted with the Motronic fuel injection
system have the ignition system incorporated
within the Motronic system (Digital Motor
Electronics or DME).
Transistorised Coil Ignition (TCI)
system
This system is has four major components;
the impulse generator, the ignition control
unit, the coil, and the spark plugs. The
impulse generator provides a timing signal for
the ignition system. Equivalent to cam-
actuated breaker points in a standard
distributor, the impulse generator creates an
A/C voltage signal every time the trigger
wheel tabs pass the impulse generator tabs.
When the ignition control unit (capacitive
discharge unit) receives the voltage signal, it
triggers a spark discharge from the coil by
interrupting the primary coil circuit. The
ignition dwell (coil charging time) is adjusted
by the ignition control unit for the most
intense spark. Note: The air gap (distance
between the impulse generator and trigger
wheel tabs) can be adjusted (see Section 11).
Ignition timing is mechanically adjusted
(see Section 7). A centrifugal advance unit
that consists of spring-loaded rotating
weights advances ignition timing as engine
speed increases. The vacuum advance
adjusts ignition timing to compensate for
changes in engine load.
Motronic ignition system
This system, also known as Digital Motor
Electronics (DME), incorporates all ignition
and fuel injection functions into one central
control unit or ECU (computer). The ignition
timing is based on inputs the ECU receives for
engine load, engine speed, coolant
temperature and intake air temperature. The
only function the distributor performs is the
distribution of the high voltage signal to the
individual spark plugs. The distributor is
attached directly to the cylinder head. There is
no mechanical spark advance system used on
these systems.
Ignition timing is electronically-controlled,
and is not adjustable on Motronic systems.
During starting, a crankshaft position sensor
(reference sensor) relays the crankshaft
position to the ECU, and an initial baseline
ignition point is determined. Once the engineis running, the ignition timing is continually
changing, based on the various input signals
to the ECU. Engine speed is signalled by a
speed sensor. Early Motronic systems have
the position reference sensor and the speed
sensor mounted on the bellhousing over the
flywheel on the left-hand side. Later Motronic
systems have a single sensor (pulse sensor)
mounted over the crankshaft pulley. This
sensor functions as a speed sensor as well as
a position reference sensor. Refer to Sec-
tion 12 for checking and renewing the ignition
sensors. Note: Some models are equipped
with a TDC sensor mounted on the front of the
engine. This sensor is strictly for the BMW
service test unit, and it is not part of the
Motronic ignition system.
Precautions
Certain precautions must be observed
when working on a transistorised ignition
system.
a) Do not disconnect the battery cables
when the engine is running
b) Make sure the ignition control unit (TCI
ignition system) is always well earthed
(see Section 10).
c) Keep water away from the distributor and
HT leads.
d) If a tachometer is to be connected to the
engine, always connect the tachometer
positive (+) lead to the ignition coil
negative terminal (-) and never to the
distributor.
e) Do not allow the coil terminals to be
earthed, as the impulse generator or coil
could be damaged.
f) Do not leave the ignition switch on for
more than ten minutes with the engine
off, or if the engine will not start.
6 Ignition system- check
2
Warning: Because of the high
voltage generated by the ignition
system, extreme care should be
taken whenever an operation is
performed involving ignition components.
This not only includes the impulse
generator (electronic ignition), coil,
distributor and spark plug HT leads, but
related components such as spark plug
connectors, tachometer and other test
equipment.
1If the engine turns over but will not start,
disconnect the spark plug HT lead from any
spark plug, and attach it to a calibrated spark
tester (available at most car accessory
shops).
Note:There are two different types of spark
testers. Be sure to specify electronic
(breakerless) ignition. Connect the clip on thetester to an earth point such as a metal
bracket (see illustration).
2If you are unable to obtain a calibrated
spark tester, remove the spark plug HT lead
from one of the spark plugs. Using an
insulated tool, hold the lead about a quarter-
inch from the engine block - make sure the
gap is not more than a quarter-inch, or
damage may be caused to the electronic
components.
3Crank the engine, and observe the tip of the
tester or spark plug HT lead to see if a spark
occurs. If bright-blue, well-defined sparks
occur, sufficient voltage is reaching the plugs
to fire the engine. However, the plugs
themselves may be fouled, so remove and
check them as described in Chapter 1.
4If there’s no spark, check another HT lead
in the same manner. A few sparks followed by
no spark is the same condition as no spark at
all.
5If no spark occurs, remove the distributor
cap, and check the cap and rotor as
described in Chapter 1. If moisture is present,
use a water-dispersant aerosol (or something
similar) to dry out the cap and rotor, then refit
the cap and repeat the spark test.
6If there’s still no spark, disconnect the coil
HT lead from the distributor cap, and
test this lead as described for the spark plug
leads.
7If no spark occurs, check the primary wire
connections at the coil to make sure they’re
clean and tight. Make any necessary repairs,
then repeat the check.
8If sparks do occur from the coil HT lead, the
distributor cap, rotor, plug HT lead(s) or spark
plug(s) may be defective. If there’s still no
spark, the coil-to-cap HT lead may be
defective. If a substitute lead doesn’t make
any difference, check the ignition coil (see
Section 9). Note:Refer to Sections 10 and 11
for more test procedures on the distributors
fitted with the TCI ignition system.
Engine electrical systems 5•3
6.1 To use a spark tester, simply
disconnect a spark plug HT lead, clip the
tester to a convenient earth (like a valve
cover bolt or nut) and operate the starter –
if there is enough power to fire the plug,
sparks will be visible between the
electrode tip and the tester body
5

and down - you should feel a slight drag on
the feeler gauge as it is moved if the gap is
correct. The gap must be as given in this
Chapter’s Specifications.
3To adjust the gap, it is necessary to remove
the impulse generator and the baseplate
assembly from the distributor (see illus-
tration 10.1).
4Follow paragraphs 17 to 24 in Section 10
and loosen the screws that retain the impulse
generator to the baseplate assembly.
5Carefully insert the feeler gauge and tighten
the screws.
6Refit the assembly back into the distributor
and recheck the adjustment.12 Ignition sensors (Motronic
system)- check and renewal
2
Note:Some models are equipped with a TDC
sensor mounted on the front of the engine.
This sensor is strictly for the BMW service test
unit, and is not part of the Motronic ignition
system.
Speed and position sensors
Check
1Locate the two electrical connectors for the
sensors (see illustrations). The grey
connector is for the position sensor, and the
white connector is for the speed sensor.
2Using an ohmmeter, check the resistance
between terminal 1 (yellow wire) and terminal
2 (black wire) on the sensor side of each
connector. The resistance should be 860 to
1,060 ohms.
3Also check the resistance between terminal
3 and either terminal 1 or terminal 2. The
resistance should be approximately 100 000
ohms.
4If the reading(s) are incorrect, renew the
sensor(s).
Renewal
5Remove the sensor mounting screw(s),using an Allen key where necessary, and pull
the sensor(s) from the sockets. Disconnect
the wiring from one sensor at a time - be sure
the connectors are not interchanged when
fitting new sensors. The bellhousing is marked
with a B for the position sensor (grey
connector) and D for the speed sensor (black
connector) (see illustration). Note: It is a
good idea to check the condition of the raised
pin on the flywheel while the sensors are out
of the sockets. Turn the engine by hand as
necessary to bring the pin into view.
6Tighten the sensor mounting screw(s)
securely, but be careful not to overtighten.
Pulse sensor (later models)
Check
7Locate the two electrical connectors for the
sensor (see illustrations). Disconnect the
electrical connector from the front.
8Using an ohmmeter, check resistance
between terminal 1 (yellow wire) and terminal
2 (black wire) on the sensor side of each
connector (see illustration). The resistance
should be 500 to 600 ohms.
9If the reading is incorrect, renew the sensor.
Renewal
10Remove the pulse sensor mounting bolt
using a 5 mm hex spanner (see illustration).
5•8 Engine electrical systems
12.10 The pulse sensor itself (arrowed) is
located on the timing belt cover, to one
side of the pulley (later models)12.8 The resistance of the pulse sensor
should be 500 to 600 ohms (later models)12.7b On later 5-Series models, the pulse
sensor connector (arrowed) is located next
to the valve cover
12.7a On later 3-Series models, the pulse
sensor connector (arrowed) is located next
to the 20-pin diagnostic connector
12.5 Location of the position sensor (B) and
speed sensor (D) on the bellhousing on all
Motronic systems – do not interchange the
sensors, or the engine will not start12.1b Location of the position sensor
(grey connector) (A) and the speed sensor
(black connector) (B) on Motronic systems
(later models)12.1a Location of the position sensor (grey
connector) (A) and the speed sensor (black
connector) (B) on Motronic systems (early
models)

Withdraw the sensor from its bracket and
remove it.
11When fitting the new sensor, use a brass
feeler gauge to position the tip of the sensor
the correct distance from the pulse wheel
(see illustration).
12Tighten the mounting bolt, but be careful
not to overtighten it.
13 Charging system- general
information and precautions
There are two different types of alternator
fitted on these models; Bosch and Motorola.
Also, there are three different amperage
ratings available; 65A, 80A or 90A. A stamped
serial number on the rear of the alternator will
identify the type and amperage rating.
Perform the charging system checks (see
Section 14) to diagnose any problems with the
alternator.
The voltage regulator and the alternator
brushes are mounted as a single assembly.
On Bosch alternators, this unit can be
removed from the alternator (see Section 16)
and the components serviced individually.
The alternator on all models is mounted on
the left front of the engine, and utilises a V-
belt and pulley drive system. Drivebelt tension
and battery servicing are the two primary
maintenance requirements for these systems.
See Chapter 1 for the procedures regarding
engine drivebelt checking and battery
servicing.
The ignition/no-charge warning light should
come on when the ignition key is turned to
Start, then go off immediately the engine
starts. If it remains on, there is a malfunction
in the charging system (see Section 14). Some
vehicles are also equipped with a voltmeter. If
the voltmeter indicates abnormally high or low
voltage, check the charging system (see
Section 14). Note:On models up to 1986, a
blown ignition/no-charge warning light will
prevent the alternator from charging. After
1987, a resistor is wired in parallel with the
warning light in order to allow current tobypass the light in the event of a broken circuit
(blown warning light).
Precautions
Be very careful when making electrical
circuit connections to the alternator, and note
the following:
a) When reconnecting wires to the alternator
from the battery, be sure to note the
polarity.
b) Before using arc-welding equipment to
repair any part of the vehicle, disconnect
the wires from the battery terminals and
from the alternator.
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.
c) Never start the engine with a battery
charger connected. Always disconnect
both battery cables before using a battery
charger.
d) Never disconnect cables from the battery
or from the alternator while the engine is
running.
e) The alternator is turned by an engine
drivebelt. Serious injury could result if
your hands, hair or clothes become
entangled in the belt with the engine
running.
f) Because the alternator is connected
directly to the battery, take care not to
short out the main terminal to earth.
g) Wrap a plastic bag over the alternator,
and secure it with rubber bands, before
steam-cleaning the engine.
14 Charging system- check
3
1If a malfunction occurs in the charging
circuit, don’t automatically assume that the
alternator is causing the problem. First check
the following items:
a) Check the drivebelt tension and condition
(see Chapter 1). Renew the drivebelt if it’s
worn or deteriorated.
b) Make sure the alternator mounting and
adjustment bolts are tight.
c) Inspect the alternator wiring harness and
the connectors at the alternator and
voltage regulator. They must be in good
condition and tight.
d) Check the fuses.
e) Start the engine and check the alternator
for abnormal noises (a shrieking or
squealing sound indicates a worn bearing,
but could also be due to a slipping
drivebelt - see a) above).f) Check the specific gravity of the battery
electrolyte. If it’s low, charge the battery
(doesn’t apply to maintenance-free
batteries).
g) Make sure the battery is fully-charged
(one bad cell in a battery can cause
overcharging by the alternator).
h) Disconnect the battery cables (negative
first, then positive). Inspect the battery
posts and the cable clamps for corrosion.
Clean them thoroughly if necessary (see
Chapter 1).
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.
2With the ignition off, connect a 12 volt test
light between the battery negative post and
the disconnected negative cable clamp. If the
test light does not come on, refit the cable
and proceed to paragraph 4. If the test light
comes on, there is a short (drain) in the
electrical system of the vehicle. The short
must be repaired before the charging system
can be checked. Note: Accessories which are
always on (such as the clock or the radio
station memory) must be disconnected before
performing this check.
3Disconnect the alternator wiring harness. If
the test light now goes out, the alternator is
faulty. If the light stays on, remove each fuse
in turn until the light goes out (this will tell you
which component is shorting out).
4Using a voltmeter, check the battery
voltage with the engine off. It should be
approximately 12 volts.
5Start the engine and check the battery
voltage again. It should now be approximately
14 to 15 volts.
6Turn on the headlights. The voltage should
drop, and then come back up, if the charging
system is working properly.
7If the voltage reading is more than the
specified charging voltage, renew the voltage
regulator (refer to Section 16). If the voltage is
less, the alternator diode(s), stator or rotor
may be faulty, or the voltage regulator may be
malfunctioning.
8If there is no short-circuit causing battery
drain but the battery is constantly
discharging, then either the battery itself is
defective, the alternator drivebelt is loose (see
Chapter 1), the alternator brushes are worn,
dirty or disconnected (see Section 17), the
voltage regulator is malfunctioning (see
Section 16) or the diodes, stator coil or rotor
coil are defective. Repairing or renewing the
diodes, stator coil or rotor coil is beyond the
scope of the home mechanic. Either renew
Engine electrical systems 5•9
12.11 The sensor tip should be set at 1.0 ±
0.3 mm from the pulse wheel
5

6
Chapter 6
Engine management and emission control systems
Catalytic converter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Electronic Control Unit (ECU) - removal and refitting . . . . . . . . . . . . 3
Evaporative emissions control (EVAP) system . . . . . . . . . . . . . . . . . 6
Evaporative emissions control system inspection . . . See Chapter 1
General information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1Information sensors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Motronic engine management system self-diagnosis -
general information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
Positive crankcase ventilation (PCV) system . . . . . . . . . . . . . . . . . . 5
6•1
Easy,suitable for
novice with little
experienceFairly easy,suitable
for beginner with
some experienceFairly difficult,
suitable for competent
DIY mechanic
Difficult,suitable for
experienced DIY
mechanicVery difficult,
suitable for expert
DIY or professional
Degrees of difficulty Contents
1 General information
To prevent pollution of the atmosphere
from incomplete combustion or evaporation
of the fuel, and to maintain good driveability
and fuel economy, a number of emission
control systems are used on these vehicles.
Not all of these systems are fitted to all
models, but they include the following:
Catalytic converter
Evaporative emission control (EVAP) system
Positive crankcase ventilation (PCV) system
Electronic engine management
The Sections in this Chapter include
general descriptions and checking
procedures within the scope of the home
mechanic, as well as component renewal
procedures (when possible) for each of the
systems listed above.
Before assuming that an emissions control
system is malfunctioning, check the fuel and
ignition systems carefully. The diagnosis of
some emission control devices requires
specialised tools, equipment and training. If
checking and servicing become too difficult,
or if a procedure is beyond your ability,
consult a dealer service department or other
specialist.This doesn’t mean, however, that emission
control systems are particularly difficult to
maintain and repair. You can quickly and
easily perform many checks, and do most of
the regular maintenance at home with
common tune-up and hand tools.
Pay close attention to any special
precautions outlined in this Chapter. It should
be noted that the illustrations of the various
systems may not exactly match the system
fitted on your vehicle because of
changes made by the manufacturer during
production.
2 Motronic engine management
system self-diagnosis-
general information
The Motronic engine management system
control unit (computer) has a built-in self-
diagnosis system, which detects malfunctions
in the system sensors and stores them as
fault codes in its memory. It is not possible
without dedicated test equipment to extract
these fault codes from the control unit.
However, the procedures given in Chapters 4
and 5 may be used to check individual
components and sensors of the Motronic
system. If this fails to pinpoint a fault, then the
vehicle should be taken to a BMW dealer, who
will have the necessary diagnostic
equipment to call up the fault codes from the
control unit. You will then have the
option to repair the fault yourself, or
alternatively have the fault repaired by the
BMW dealer.
3 Electronic control unit (ECU)
- removal and refitting
2
Removal
1The Electronic Control Unit (ECU) is located
either inside the passenger compartment
under the right-hand side of the facia panel on
3-Series models, or in the engine
compartment on the right-hand side on 5-
Series models (see Chapter 4).
2Disconnect 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.
3First remove the access cover on models
with the ECU on the right-hand side of the
engine compartment (see Chapter 4).
4If the ECU is located inside the vehicle,
remove the access cover on the right-hand side.
5Unplug the electrical connectors from the
ECU.
6Remove the retaining bolts from the ECU
bracket.
7Carefully remove the ECU. Note: Avoid static
electricity damage to the ECU by wearing rubber
gloves, and do not touch the connector pins.
Refitting
8Refitting is a reversal of removal.
The most frequent cause of
emission system problems is
simply a leaking vacuum hose
or loose wire, so always
check the hose and wiring connections
first.