1991 BMW 5 SERIES Crank sensor

12After the No 1 piston has been positioned
at TDC on the compression stroke, TDC for
any of the remaining pistons can be located
by turning the crankshaft and following the
firing order. Mark the remaining spark plug
lead terminal locations just like you did for the
No 1 terminal, then number the marks to
correspond with the cylinder numbers. As you
turn the crankshaft, the rotor will also turn.
When it’s pointing directly at one of the marks
on the distributor, the piston for that particular
cylinder is at TDC on the compression stroke.
4 Valve cover-
removal and refitting
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.
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
1Disconnect the battery negative cable.
2Detach the breather hose from the valve
cover.
3On M20 engines, unbolt and remove the
intake manifold support bracket and, if
applicable, the bracket for the engine sensors
or idle air stabiliser (it will probably be
necessary to disconnect the electrical
connectors from the sensors and stabiliser).
4On M30 engines, disconnect the electrical
connector for the airflow sensor. Unclip the
electrical harness, moving it out of the way.
5Where necessary on M30 engines, remove
the hoses and fittings from the intake air hose,
then loosen the clamp and separate the hose
from the throttle body. Unscrew the mounting
nuts for the air cleaner housing, and remove
the housing together with the air hose and
airflow sensor.
6Remove the valve cover retaining nuts and
washers (see illustrations). Where necessary,
disconnect the spark plug lead clip or coverfrom the stud(s), and set it aside. It will usually
not be necessary to disconnect the leads from
the spark plugs.
7Remove the valve cover and gasket.
Discard the old gasket. On the M40 engine,
also remove the camshaft cover (see
illustrations). If applicable, remove the semi-
circular rubber seal from the cut-out at the
front of the cylinder head.
Refitting
8Using a scraper, remove all traces of old
gasket material from the sealing surfaces of
the valve cover and cylinder head.
Caution: Be very careful not to
scratch or gouge the delicate
aluminium surfaces. Gasket
removal solvents are available at
motor factors, and may prove helpful.
After all gasket material has been
removed, the gasket surfaces can be
degreased by wiping them with a rag
dampened with a suitable solvent.
9If applicable, place a new semi-circular
rubber seal in the cut-out at the front of the
cylinder head, then apply RTV-type gasket
sealant to the joints between the seal and the
mating surface for the valve cover gasket.
Note:After the sealant is applied, you should
refit the valve cover and tighten the nuts within
ten minutes.
10Refit the camshaft cover (M40 engine), the
valve cover and a new gasket. Refit the
washers and nuts; tighten the nuts evenly and
securely. Don’t overtighten these nuts - theyshould be tight enough to prevent oil from
leaking past the gasket, but not so tight that
they warp the valve cover.
11The remainder of refitting is the reverse of
removal.
5 Intake manifold-
removal and refitting
2
Removal
1Allow the engine to cool completely, then
relieve the fuel pressure on fuel-injection
engines (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.
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.
3Drain the engine coolant (see Chapter 1)
below the level of the intake manifold. If the
coolant is in good condition, it can be saved
and reused.
4On fuel injection engines, loosen the hose
clamp and disconnect the large air inlet hose
from the throttle body. It may also be
necessary to remove the entire air
cleaner/inlet hose assembly to provide
enough working room (see Chapter 4).
2A•4 In-car engine repair procedures
4.7b Removing the camshaft cover on the
M40 engine4.7a Removing the valve cover on the
M40 engine4.7c Removing the valve cover gasket on
the M40 engine
4.6b Valve cover bolt locations (arrowed)
on M20 six-cylinder engines4.6a Valve cover bolt locations (arrowed)
on M10 four-cylinder engines

6 Exhaust manifold-
removal and refitting
1
Warning: Make sure the engine is
completely cool before beginning
work on the exhaust system.
Caution: If the radio in your
vehicle is equipped with an anti-
theft system, make sure you
have the correct activation code
before disconnecting the battery.
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.
2On models where the air cleaner is on the
exhaust manifold side of the engine, remove
the air cleaner housing assembly and/or
airflow sensor to provide sufficient working
area (see Chapter 4, if necessary).
3Unplug the HT leads and set the spark plug
lead harness aside (see Chapter 1).
4Clearly label, then disconnect or remove, all
wires, hoses, fittings, etc. that are in the way.
Be sure to disconnect the oxygen sensor,
where fitted.
5Raise the vehicle, and support it securely
on axle stands. Working from under the
vehicle, separate the exhaust downpipe from
the manifold. Use penetrating oil on the
fasteners to ease removal (see illustrations).
6Remove the axle stands, and lower the
vehicle. Working from the ends of the
manifold toward the centre, loosen the
retaining nuts gradually until they can be
removed. Again, penetrating oil may prove
helpful.
7Pull the manifold off the head, then remove
the old gaskets (see illustrations). Note:Be
very careful not to damage the oxygen sensor,
where fitted.8Clean the gasket mating surfaces of the
head and manifold, and make sure the
threads on the exhaust manifold studs are in
good condition.
9Check for corrosion, warping, cracks, and
other damage. Repair or renew the manifold
as necessary.
10When refitting the manifold, use new
gaskets. Tighten the manifold-to-head
retaining nuts gradually, starting at the centre
and working out to the ends, to the torque
listed in this Chapter’s Specifications. Also
tighten the downpipe-to-manifold nuts.
11The remaining steps are simply a reversal
of the removal procedure.
7 Timing chain covers-
removal and refitting
5
Note 1:This procedure applies to M10 and
M30 engines.
Note 2:The upper timing chain cover can be
removed separately. If you need to remove
both the upper and lower covers, special tools
are required. Read paragraphs 8 and 9 before
beginning work.
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.
2If you’re removing the lower timing chain
cover (the upper cover can be removed
separately), remove the cooling fan and fan
shroud, the radiator and the fan drivebelt
pulley (see Chapter 3).
3On the M10 engine only, remove the water
pump (see Chapter 3).
4On engines where the distributor cap is
mounted directly to the timing chain cover,
remove the cap, rotor and the black plastic
cover beneath the rotor (see Chapter 1).
5On the M30 engine fitted with the
L-Jetronic fuel system, remove the
distributor from the upper timing cover (see
Chapter 5).
6Remove the valve cover (see Section 4).
7If you’ll be removing the lower timing chain
cover on the M30 engine, remove the crankshaft
pulley from the vibration damper/hub. Hold the
pulley stationary with a socket on the centre
bolt, and remove the pulley bolts with another
socket (see illustration).
8If you’ll be removing the lower timing chain
2A•6 In-car engine repair procedures
6.7c Removing the exhaust manifold-to-
downpipe gasket (M40 engine)6.7b Removing the exhaust manifold
gasket (M40 engine)6.7a Removing the exhaust manifold
(M40 engine)
6.5b Exhaust manifold-to-downpipe flange
(M40 engine)6.5a Remove the exhaust manifold nuts
(arrowed) from the exhaust pipe (M20
engine) - soaking the nuts with penetrating
oil should make them easier to remove
Remove the windscreen
washer reservoir from the
right-hand side of the engine
compartment to give more
working room.

5If applicable, disconnect the reference
sensor wiring harness which runs across the
front of the timing belt cover, and set it aside.
6If the distributor cap is mounted directly to
the upper timing belt cover, remove the cap,
rotor and the black plastic cover beneath the
rotor (see illustrations).
7Remove the lower fan drivebelt pulley and
vibration damper. Secure the crankshaft
pulley centre bolt while you loosen the outer
pulley/damper bolts (see illustration 7.7).
8Remove the bolts/nuts attaching the timing
belt covers to the engine (see illustration).
9Remove the upper cover first, then the
lower cover (see illustrations). Note: The
upper cover has two alignment sleeves in the
top bolt positions. Be sure these are in place
upon reassembly.
10Refitting is the reverse of the removal
procedure. Tighten the cover bolts securely.
10 Timing belt and sprockets-
removal, inspection and
refitting
5
Note 1:This procedure applies to M20 and
M40 engines.
Note 2:Before removing the camshaft
sprocket on the M40 engine, it is necessary to
obtain a tool to hold the camshaft for the
refitting procedure (see paragraph 10).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.
Removal1Disconnect the negative cable from the
battery.
2Remove the timing belt covers (see Sec-
tion 9).
3On the M40 engine, drain the cooling
system (see Chapter 1), then disconnect thehose, unbolt the thermostat housing and
remove the thermostat (see Chapter 3).
4Set the No 1 piston at TDC (see Section 3).
Caution: Once the engine is set at
TDC, do not rotate the camshaft
or crankshaft until the timing belt
is refitted. If the crankshaft or
camshaft is rotated with the timing belt
removed, the valves could hit the pistons,
causing expensive internal engine damage.
5On the M20 engine, the crankshaft mark
should be aligned with the mark on the inner
cover(see illustration). The mark on the
camshaft sprocket should be aligned with the
stamped line on the cylinder head (see
illustration). On the M40 engine, make an
In-car engine repair procedures 2A•9
9.8 Remove all the nuts/ bolts (arrowed)
that attach the upper and lower covers
(M20 engine - removed for clarity)9.6c . . . and remove the black plastic
cover9.6b . . . then unbolt the rotor . . .
9.9c Removing the lower timing belt cover
on the M40 engine9.9b Removing the upper timing belt cover
on the M40 engine
10.5b Align the mark on the camshaft
sprocket with the mark on the cylinder
head (arrowed)10.5a Align the groove in the hub on the
end of the crankshaft with the notch in the
front inner cover (arrowed) and mark them
for assembly reference later on
9.9a Remove the upper timing belt cover
first, then the lower cover (M20 engine)
1 Upper timing belt cover
2 Lower timing belt cover
2A

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

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

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.

slightly by hand. Release the throttle slowly
until it reaches 0.2 to 0.6 mm from the throttle
stop. There should be continuity.
29Check the resistance between terminals 3
and 18 as the throttle is opened. There should
be continuity when the throttle switch is within
8 to 12 degrees of fully-open. If the readings
are incorrect, adjust the TPS.
30If all the resistance readings are correct
and the TPS is properly adjusted, check for
power (5 volts) at the sensor, and if necessary
trace any wiring circuit problems between the
sensor and ECU (see Chapter 12).
Adjustment
31If the adjustment is not as specified
(paragraphs 28 to 30), loosen the screws on
the TPS, and rotate the sensor into the correct
adjustment. Follow the procedure for
checking the TPS given above, and tighten
the screws when the setting is correct.
32Recheck the TPS once more; if the
readings are correct, reconnect the TPS
harness connector.
Early 535i models with automatic
transmission
Check
33First test the continuity of the TPS. Follow
paragraphs 28 to 30 and check for continuity.
34Next, test the idle position switch (see
illustration). Unplug the electrical connector
in the idle position switch harness, andconnect an ohmmeter to terminals 1 and 2.
There should be continuity. Open the throttle
slightly, and measure the resistance. There
should now be no continuity.
35Check for the correct voltage signals from
the TPS, with the throttle closed and the
ignition on. Probe the back of the TPS
connector with a voltmeter, and check for
voltage at terminal 3 (black wire) and earth.
There should be 5 volts present. Also, probe
terminal 3 (black wire) and terminal 1 (brown
wire). There should be 5 volts present here
also.
36Check for voltage at terminal 2 (yellow
wire) and terminal 1 (brown wire), and slowly
open the throttle. The voltage should increase
steadily from 0.7 volts (throttle closed) to
4.8 volts (throttle fully-open).
Adjustment
37First measure the stabilised voltage. With
the ignition on and the throttle closed,
measure the voltage between terminal 3
(black wire) and terminal 1 (brown wire). It
should be about 5 volts.
38Next, loosen the sensor mounting screws,
and connect the voltmeter to terminal 2
(yellow wire) and terminal 3 (black wire). With
the throttle fully open, rotate the switch until
there is 0.20 to 0.24 volts less than the
stabilised voltage. Note: You will need a
digital voltmeter to measure these small
changes in voltage.
39Recheck the TPS once more; if the
readings are correct, reconnect the TPS
electrical connector. It is a good idea to lock
the TPS screws with paint or thread-locking
compound.
Airflow meter
General description
40The airflow meter is located on the air
intake duct. The airflow meter measures the
amount of air entering the engine. The ECU
uses this information to control fuel delivery. A
large volume of air indicates acceleration,
while a small volume of air indicates
deceleration or idle. Refer to Chapter 4 for all
the diagnostic checks and renewal
procedures for the airflow meter.
Ignition timing sensors
41Ignition timing is electronically-controlled
on Motronic systems, and is not adjustable.
During starting, a crankshaft position sensor
relays the crankshaft position to the ECU, and
an initial baseline ignition point is determined.
Once the engine is running, the ignition point
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 reference sensor and the
speed sensor mounted on the bellhousing
over the flywheel. 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 sensor. Refer to Chapter 5 for more
information. 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.
5 Positive crankcase
ventilation (PCV) system
1The Positive Crankcase Ventilation (PCV)
system (see illustration)reduces
hydrocarbon emissions by scavenging
crankcase vapours. It does this by circulating
blow-by gases and then re-routing them to
the intake manifold by way of the air cleaner.
2This PCV system is a sealed system. The
crankcase blow-by vapours are routed
directly to the air cleaner or air collector with
crankcase pressure behind them. The vapour
is not purged with fresh air on most models or
6•4 Engine management and emission control systems
5.2 PCV hose being removed from the
valve cover5.1 Diagram of the PCV system on the
M20 engine (others similar)4.34 Idle position switch and TPS on early
535i models with automatic transmission
4.28c . . . then check for continuity
between terminals 3 and 18 as the throttle
is opened

filtered with a flame trap like most
conventional systems. There are no
conventional PCV valves fitted on these
systems - just a hose (see illustration).
3The main components of the PCV system
are the hoses that connect the valve cover to
the throttle body or air cleaner. If abnormal
operating conditions (such as piston ring
problems) arise, the system is designed to
allow excessive amounts of blow-by gases to
flow back through the crankcase vent tube
into the intake system, to be consumed by
normal combustion. Note: Since these
models don’t use a filtering element, it’s a
good idea to check the PCV system
passageways for clogging from sludge and
combustion residue(see illustration).
6 Evaporative emissions
control (EVAP) system
2
General description
Note:This system is normally only fitted to
those vehicles equipped with a catalytic
converter.
1When the engine isn’t running, the fuel in the
fuel tank evaporates to some extent, creating
fuel vapour. The evaporative emissions control
system (see illustration)stores these fuel
vapours in a charcoal canister. When the
engine is cruising, the purge control valve is
opened slightly, and a small amount of fuel
vapour is drawn into the intake manifold and
burned. When the engine is starting cold or
idling, the purge valve prevents any vapours
from entering the intake manifold and causing
excessively-rich fuel mixture.
2Two types of purge valve are used;
electrically-operated or vacuum-operated. To
find out which type is on your vehicle, follow
the hose from the charcoal canister until you
locate the purge valve. Some are located on
the intake manifold, and others near the
charcoal canister. Look for either an electrical
connector, or vacuum lines, to the purge
valve.3A faulty EVAP system will only affect engine
driveability when the engine is warm. The
EVAP system is not usually the cause of
difficult cold starting or any other cold-running
problems.
Check
Vacuum-operated purge valve
4Remove the vacuum lines from the purge
valve, and blow into the larger valve port. It
should be closed, and not pass any air. Note:
Some models have a thermo-vacuum valve
that delays canister purging until the coolant
temperature reaches approximately 46º C.
Check this valve to make sure that vacuum is
controlled at the proper temperatures. The
valve is usually located in the intake manifold,
near the thermo-time switch and the coolant
temperature sensor.
5Disconnect the small vacuum hose from the
purge valve, and apply vacuum with a hand-
held vacuum pump. The purge valve should
be open, and air should be able to pass
through.6If the test results are unsatisfactory, renew
the purge valve.
Electrically-operated purge valve
7Disconnect any lines from the purge valve,
and (without disconnecting the electrical
connector) place it in a convenient spot for
testing.
8Check that the valve makes a “click” sound
as the ignition is switched on (see
illustration).
9If the valve does not “click”, disconnect the
valve connector, and check for power to the
valve using a test light or a voltmeter (see
illustration).
10If battery voltage is present, but the valve
does not work, renew it. If there is no voltage
present, check the Motronic control unit and
the wiring.
Canister
11Mark all the hoses for position, then
detach them from the canister.
12Slide the canister out of its mounting clip.
Engine management and emission control systems 6•5
6.1 Diagram of the EVAP system on the M10 engine (others similar)
6.9 Check for battery voltage at the
electrical connector to the purge valve6.8 When the ignition is switched on, there
should be a distinct “click” from the purge
valve
6
5.3 It’s a good idea to check for excess
residue from the crankcase vapours
circulating in the hoses and ports - this
can eventually clog the system, and cause
a pressure increase in the engine block