1991 BMW 3 SERIES check oil

8Remove the hold-down nut or bolt and
clamp.
9Remove the distributor. Note:Do not rotate
the engine with the distributor out.
Refitting
10Before refitting the distributor, make
certain No 1 piston is still at TDC on the
compression stroke.
11Insert the distributor into the engine, with
the adjusting clamp centred over the hold-
down hole. Make allowance for the gear to
turn as the distributor is inserted.
12Refit the hold-down nut or bolt. The marks
previously made on the distributor housing,
and on the rotor and engine, should line up
before the nut or bolt is tightened.
13Refit the distributor cap.
14Connect the wiring for the distributor.
15Reconnect the spark plug HT leads.
16Reconnect the vacuum hoses as
previously marked.
17Check the ignition timing (see Section 7).
Motronic system
Removal
18Remove the cover from the distributor
(see illustration)and remove the distributor
cap (see Chapter 1).
19Using a small Allen key, remove the three
screws from the rotor (see illustration).
20Remove the rotor.
Refitting
21Refitting is the reverse of removal.
9 Ignition coil -
check and renewal
2
Caution: Do not earth the coil, as
the coil and/or impulse generator
could be damaged.
Note:On models equipped with the Motronic
system, a faulty ECU can cause the ignition
coil to become damaged. Be sure to test the
ignition coil if the engine will not start and an
ECU fault is suspected.
1Mark the wires and terminals for position,
then remove the primary circuit wires and the
HT lead from the coil.2Remove the coil assembly from its
mounting, then clean the outer casing and
check it for cracks and other damage.
3Inspect the coil primary terminals and the
coil tower terminal for corrosion. Clean them
with a wire brush if any corrosion is found.
4Check the coil primary resistance by
attaching an ohmmeter to the primary
terminals (see illustrations). Compare the
measured resistance to the Specifications
listed in this Chapter.
5Check the coil secondary resistance by
connecting one of the ohmmeter leads to one
of the primary terminals, and the other
ohmmeter lead to the coil high-tension
terminal (see illustrations). On TCI systems,
Engine electrical systems 5•5
8.19 Remove the rotor screws (arrowed)
with an Allen key, and pull the rotor off the
shaft8.18 Remove the three bolts (arrowed)
from the distributor cap8.7 Mark the relationship of the rotor to
the distributor housing (arrowed)
9.5b Using an ohmmeter, measure the
secondary resistance of the coil (later
Motronic system)9.5a Using an ohmmeter, measure the
secondary resistance of the coil (TCI
system)
9.4b Some Motronic systems use a
different type of coil. First, remove the coil
cover and . . .9.4a Using an ohmmeter, measure the
resistance between the primary terminals
of the ignition coil (TCI system shown)
9.4c . . . using an ohmmeter, measure the
resistance between the primary terminals
of the coil
5

connect the ohmmeter to coil terminal 1 (-)
and the centre tower. On Motronic systems,
connect the ohmmeter to coil terminal 15 (+)
and the centre tower. Compare the measured
resistance with the values given in the Specifi-
cations in this Chapter.
6If the measured resistances are not close to
those specified, the coil is defective and
should be renewed. Note that the measured
resistance will vary according to the
temperature of the coil, so don’t rush to
condemn the coil if the resistance is only a
little way out.
7It is essential for proper ignition system
operation that all coil terminals and wire leads
be kept clean and dry.
8Refit the coil in its mounting, and reconnect
the wiring. Refitting is the reverse of removal.
10 Impulse generator and
ignition control unit- check
and renewal (TCI system)
3
1The impulse generator (located in the
distributor) and ignition control unit need to be
tested in the event there is no spark at the
spark plugs. Make sure the plug leads,
ignition coil and spark plugs are working
properly (see Sections 6 and 9). There are two
types of control units; Bosch or
Siemens/Telefunken. The two types (see
illustration)can be distinguished by their
electrical connectors. The Bosch type uses a
single, large rectangular connector at the
bottom of the unit, while the
Siemens/Telefunken control unit uses two
round electrical connectors at the front of the
unit.
Check
Voltage supply and earth to ignition
control unit
2With the ignition off, remove the harness
connectors from the ignition control unit (see
illustrations). Connect a voltmeter between
connector terminals 2 and 4 on Bosch
systems, or between terminals 6 and 3 on
Siemens/Telefunken systems.
3Turn the ignition on. There should be
battery voltage on the designated terminals. If
there is no voltage, check the wiring harness
for an open-circuit (see Chapter 12).
4Using an ohmmeter, check for continuity
between connector terminal 2 (Bosch) or 6
(Siemens/Telefunken) and the earth to the
vehicle body. Continuity should exist.
5Using an ohmmeter, check for continuity
between connector terminal 4 (Bosch) or 3
(Siemens/Telefunken) and terminal 15 of the
ignition coil. Continuity should exist.
6If the readings are incorrect, repair the
wiring harness.
Impulse generator signal
7If the ignition control unit is receiving
battery voltage, check the A/C signal voltage
coming from the impulse generator to the
control unit.
5•6 Engine electrical systems
10.2b Check for voltage at terminals 6 and
3 on the control unit electrical connector
(Siemens/Telefunken system shown)10.2a Check for voltage at terminals 2 and
4 on the control unit electrical connector
(Bosch system shown)
1 Coil HT lead
2 Ignition coil
3 Spark plug HT lead
4 Spark plug
5 Ignition control unit (Bosch)
6 Ignition control unit
(Siemens/Telefunken)
7 Wiring harness8 Distributor housing with
centrifugal advance
counterweights
9 Vacuum diaphragm
10 Circlip
11 Impulse generator
12 Trigger wheel
13 Circlip
14 Dust shield15 Ignition rotor
16 Distributor
17 Roll pin
18 Trigger wheel and impulse
generator tabs
19 Cap retaining clip
20 Impulse generator
connector
10.1 Schematic of the ignition components used on engines with the TCI system

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

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

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.
Bosch alternator
2Remove the voltage regulator from the back
of the alternator (see Section 16).
3Measure the length of the brushes (see
illustration). They should not be less than
6.0 mm. If any are worn past this point, renew
them all as a set. 4Also check for excessively worn slip rings
(see illustration 16.5).
5The brushes are retained either by set
screws or by solder. If you are not skilled at
soldering, it may be best to have an auto
electrician fit the new brushes. Note: Be
careful not to apply heat to the solder joint for
more than 5 seconds. If necessary, use a heat
sink to capture the excess heat. This can be
accomplished by clamping a pair of needle-
nose pliers next to the solder joint.
6On the screw type, hold the assembly in
place and refit the screws. Tighten them
evenly, a little at a time, so the holder isn’t
distorted.
7Refit the regulator assembly to the
alternator.8Reconnect the battery negative cable.
Motorola alternator
9Remove the alternator.
10The brushes are mounted under the
regulator on the rear of the alternator (see
illustration 16.7).
11Remove the mounting screws and
insulating washers, and separate the voltage
regulator and brush holder from the brush end
housing.
12Measure the length of the brushes (see
illustration 17.3). If any brush is less then
6.0 mm long, renew them all as a set.
13Make sure the brushes move smoothly in
the holder.
14Refit the brush holder/regulator. Tighten
the screws securely. Make sure the brushes
aren’t earthed.
15Refitting is the reverse of removal.
18 Starting system- general
information and precautions
The sole function of the starting system is
to turn over the engine quickly enough to
allow it to start.
The starting system consists of the battery,
the starter motor, the starter solenoid, the
ignition switch, and the wires connecting
them. The solenoid is mounted directly on the
starter motor. The starter/solenoid motor
assembly is fitted on the lower part of the
engine, next to the transmission bellhousing.
When the ignition key is turned to the Start
position, the starter solenoid is actuated
through the starter control circuit. The starter
solenoid then connects the battery to the
starter, and moves the starter pinion into
mesh with the flywheel ring gear. The battery
supplies the electrical energy to the starter
motor, which does the actual work of cranking
the engine.
The starter motor on some manual
transmission vehicles can only be operated
when the clutch pedal is depressed. On a
vehicle equipped with automatic
transmission, the starter can only be operated
Engine electrical systems 5•11
17.3 Check the brush length in the normal
rest position (spring uncoiled)
5
16.7 Exploded view of the Motorola alternator

when the transmission selector lever is in Park
or Neutral.
Always detach the battery negative cable
before working on the starting system.
19 Starter motor-
in-vehicle check
2
Note:Before diagnosing starter problems,
make sure the battery is fully charged.
1If the starter motor does not turn at all when
the switch is operated, make sure that the
gear lever is in Neutral or Park (automatic
transmission) or, where applicable, that the
clutch pedal is depressed (manual
transmission).
2Make sure that the battery is charged, and
that all cables, both at the battery and starter
solenoid terminals, are clean and secure.
3If the starter motor spins but the engine is
not cranking, the overrun clutch in the starter
motor is slipping, and the starter motor must
be renewed.
4If, when the switch is actuated, the starter
motor does not operate at all but the solenoid
clicks, then the problem lies either in the
battery, the main solenoid contacts, or the
starter motor itself (or the engine is seized).
5If the solenoid plunger cannot be heard
when the switch is actuated, the battery is
faulty, the switch is defective, the fusible link
is burned-out (the circuit is open), or the
solenoid itself is defective.
6To check the solenoid, connect a jumper
lead between the battery (+) and the ignition
switch wire terminal (the small terminal) on the
solenoid. If the starter motor now operates,
the solenoid is OK and the problem is in the
ignition switch, starter inhibitor switch
(automatic transmission models), clutch
switch (some manual transmission models), or
the wiring.
7If the starter motor still does not operate,
remove the starter/solenoid assembly for
dismantling, testing and repair.
8If the starter motor cranks the engine at an
abnormally-slow speed, first make sure that
the battery is charged, and that all terminal
connections are tight. If the engine is partially-
seized, or has the wrong viscosity oil in it, it
will crank slowly.
9Run the engine until normal operating
temperature is reached, then disconnect the
coil HT lead from the distributor cap and earth
it on the engine.
10Connect a voltmeter positive lead to the
battery positive post, and connect the
negative lead to the negative post.11Crank the engine, and take the voltmeter
readings as soon as a steady figure is
indicated. Do not allow the starter motor to
turn for more than 10 seconds at a time. A
reading of 9 volts or more, with the starter
motor turning at normal cranking speed, is
normal. If the reading is 9 volts or more but
the cranking speed is slow, the solenoid
contacts are burned, there is a bad
connection, or the starter motor itself is faulty.
If the reading is less than 9 volts and the
cranking speed is slow, the starter motor is
faulty or the battery is responsible (defective
or discharged).
20 Starter motor-
removal and refitting
1
Note:If the starter motor is defective, it should
be renewed, or taken to an auto electrical
specialist for repair. Overhaul of the starter
motor is unlikely to be a practical proposition
for the home mechanic, even if spare parts are
available. However, the solenoid can be
renewed separately (see Section 21).
Removal
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.
1Detach the battery negative cable.
2Raise the vehicle and support it securely on
axle stands.
3Clearly label the wires from the terminals onthe starter motor and solenoid, then
disconnect them. Note: On some models, it
may be necessary to remove the air cleaner
(see Chapter 4), coolant expansion tank (see
Chapter 3) and the heater hoses to gain
access to the top of the starter. Carefully label
any hoses or components that need to be
removed from the engine compartment, to
avoid confusion when reassembling.
4Unscrew the mounting bolts and detach the
starter (see illustrations).
Refitting
5Refitting is the reverse of removal.
21 Starter solenoid-
removal and refitting
1
Removal
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.
2Remove the starter motor (see Section 20).
3Disconnect the cable from the solenoid to
the starter motor terminal.
4Remove the screws which secure the
solenoid to the starter motor.
5Detach the solenoid from the starter body.
6Remove the plunger and plunger spring.
Refitting
7Refitting is the reverse of removal.
5•12 Engine electrical systems
20.4b Withdrawing the starter motor from
the M40 engine20.4a Working under the vehicle, remove
the starter lower mounting bolt and nut
(arrowed)

On some models, it will be necessary to
release the retaining clip (see illustration).
13Visually examine the canister for leakage
or damage.
14Renew the canister if you find evidence of
damage or leakage.
7 Catalytic converter
1
General description
1To reduce emissions of unburnt
hydrocarbons (HC), carbon monoxide (CO)
and oxides of nitrogen (NOx), the later
vehicles covered by this manual are equipped
with a catalytic converter (see illustration).
The converter contains a ceramic honeycomb
coated with precious metals, which speed up
the reaction between the pollutants listed
previously and the oxygen in the exhaust gas.
The pollutants are oxidised to produce water
(H
2O), nitrogen and carbon dioxide (CO2).
Check
2Visually examine the converter(s) for cracks
or damage. Make sure all nuts and bolts are
tight.
3Inspect the insulation cover (if applicable)
welded onto the converter - it should not be
loose.
Caution: If an insulation cover is
dented so that it touches the
converter housing inside,
excessive heat may be
transferred to the floor.
4Start the engine and run it at idle speed.
5Check for exhaust gas leakage from the
converter flanges. Check the body of each
converter for holes.
Component renewal
6See Chapter 4 for removal and refitting
procedures.
Precautions
7The catalytic converter is a reliable and
simple device, which needs no maintenance
in itself, but there are some facts of which an
owner should be aware, if the converter is to
function properly for its full service life.
(a) DO NOT use leaded (eg UK “4-star”)
petrol in a car equipped with a catalytic
converter - the lead will coat the precious
metals, reducing their converting
efficiency, and will eventually destroy the
converter.
(b) Always keep the ignition and fuel systems
well-maintained in accordance with the
manufacturer’s schedule, as given in
Chapter 1. In particular, ensure that the air
cleaner filter element, the fuel filter (where
fitted) and the spark plugs are renewed at
the correct interval. If the intake air/fuel
mixture is allowed to become too rich due
to neglect, unburned fuel will enter the
catalytic converter, overheating the
element and eventually destroying the
converter.
(c) If the engine develops a misfire, do not
drive the car at all (or at least as little as
possible) until the fault is cured - the
misfire will allow unburned fuel to enter
the converter, which will result in its
overheating, as noted above.
(d) DO NOT push- or tow-start the car - this
will soak the catalytic converter in
unburned fuel, causing it to overheat
when the engine does start - see (b) or (c)
above.
(e) DO NOT switch off the ignition at high
engine speeds - ie do not “blip” the
throttle immediately before switching offthe engine. If the ignition is switched off
at anything above idle speed, unburned
fuel will enter the (very hot) catalytic
converter, with the possible risk of its
igniting on the element and damaging the
converter.
(f) DO NOT use fuel or engine oil additives -
these may contain substances harmful to
the catalytic converter.
(g) DO NOT continue to use the car if the
engine burns oil to the extent of leaving a
visible trail of blue smoke - the unburned
carbon deposits will clog the converter
passages, and reduce its efficiency; in
severe cases, the element will overheat.
(h) Remember that the catalytic converter
operates at very high temperatures -
hence the heat shields on the car’s
underbody - and the casing will become
hot enough to ignite combustible
materials which brush against it. DO NOT,
therefore, park the car in dry
undergrowth, or over long grass or piles
of dead leaves.
(i) Remember that the catalytic converter is
FRAGILE - do not strike it with tools
during servicing work, and take great care
when working on the exhaust system.
Ensure that the converter is well clear of
any jacks or other lifting gear used to raise
the car, and do not drive the car over
rough ground, road humps, etc, in such a
way as to “ground” the exhaust system.
(j) In some cases, particularly when the car
is new and/or is used for stop/start
driving, a sulphurous smell (like that of
rotten eggs) may be noticed from the
exhaust. This is common to many
catalytic converter-equipped cars, and
seems to be due to the small amount of
sulphur found in some petrols reacting
with hydrogen in the exhaust, to produce
hydrogen sulphide (H
2S) gas; while this
gas is toxic, it is not produced in sufficient
amounts to be a problem. Once the car
has covered a few thousand miles, the
problem should disappear - in the
meanwhile, a change of driving style, or of
the brand of petrol used, may effect a
solution.
(k) The catalytic converter, used on a well-
maintained and well-driven car, should
last for 50 000 to 100 000 miles - from
this point on, the CO level should be
carefully checked regularly, to ensure that
the converter is still operating efficiently. If
the converter is no longer effective, it
must be renewed.
6•6 Engine management and emission control systems
7.1 Typical catalytic converter (M10
engine type shown, others similar)6.12 EVAP system charcoal canister
viewed from under the vehicle (316i model)

Inspection
1Loosen the wheel bolts, raise the vehicle
and support it securely on axle stands.
Remove the wheel, and refit three bolts to
hold the disc in place. If the rear brake disc is
being worked on, release the handbrake.
2Remove the brake caliper as outlined in
Section 4. It is not necessary to disconnect
the brake hose. After removing the caliper,
suspend it out of the way with a piece of wire.
Remove the caliper mounting bracket (see
illustration).
3Inspect the disc surface for scoring, cracks
or other damage. Light scratches and shallow
grooves are normal after use, and are not
usually detrimental to brake operation, but
deep scoring requires disc removal andrenewal, or (if possible) refinishing by a
specialist. If a disc is cracked it must be
renewed. Be sure to check both sides of the
disc (see illustration). If severe vibration has
been noticed during application of the brakes,
the discs may be warped (excessive run-out).
If the vehicle is equipped with the Anti-lock
Braking System (ABS), do not confuse
vibration caused by warped discs with normal
operation of the ABS. It is quite normal for
some vibration to be felt through the pedal
when the system is working.
4To check disc run-out, place a dial indicator
at a point about 13 mm from the outer edge of
the disc (see illustration). Set the indicator to
zero, and rotate the disc. The indicator
reading should not exceed the specifiedallowable run-out limit. If it does (and if the
run-out is not due to wheel bearing wear), the
disc should be renewed or (if possible)
refinished by a specialist. Note:It is
recommended that the discs be resurfaced
regardless of the dial indicator reading, as this
will impart a smooth finish and ensure a
perfectly flat surface, eliminating any vibration
felt through the brake pedal or other
undesirable symptoms related to questionable
discs. At the very least, if you elect not to have
the discs resurfaced, remove the glazing from
the surface with emery cloth or sandpaper,
using a swirling motion (see illustration).
5It is absolutely critical that the disc not be
machined to a thickness less than that
specified. The minimum wear (or discard)
thickness is stamped into the hub of the disc.
The disc thickness can be checked with a
micrometer (see illustration).
Removal
6Remove the disc retaining screw (see
illustration) and remove the disc from the hub
(see illustration). If the disc is stuck to the
hub, spray a generous amount of penetrating
oil onto the area between the hub and the disc
(see illustration)and allow a few minutes for
it to loosen the rust between the two
components. If a rear disc still sticks, insert a
thin, flat-bladed screwdriver through the hub
flange, rotate the starwheel on the handbrake
9•6 Braking system
5.6c If the disc is stuck to the hub, spray
some penetrating oil onto the area
between the hub and the disc, and give the
oil a few minutes to separate the two parts
5.6b . . . and remove the disc from
the hub5.6a Remove the disc retaining screw . . .
5.5 The disc thickness can be checked
with a micrometer5.4b Using a swirling motion, remove the
glaze from the disc surface with
sandpaper or emery cloth
5.4a To check disc run-out, mount a dial
indicator as shown, and rotate the disc5.3 The brake pads on this vehicle were
obviously neglected, as the backing plate
cut deep grooves into the disc - wear this
severe means the disc must be renewed5.2 Remove the caliper mounting bracket
bolts (arrowed) and remove the bracket