1990 BMW 3 SERIES Coolant type

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

4 Information sensors
2
Note:Refer to Chapters 4 and 5 for additional
information on the location and diagnosis of
the information sensors that are not covered in
this Section.
Coolant temperature sensor
General description
1The coolant temperature sensor (see
illustration)is a thermistor (a resistor which
varies its resistance value in accordance with
temperature changes). The change in the
resistance value regulates the amount of
voltage that can pass through the sensor. At
low temperatures, the sensor’s resistance is
high. As the sensor temperature increases, its
resistance will decrease. Any failure in this
sensor circuit will in most cases be due to a
loose or shorted-out wire; if no wiring
problems are evident, check the sensor as
described below.
Check
2To check the sensor, first check its
resistance (see illustration)when it is
completely cold (typically 2100 to 2900 ohms).
Next, start the engine and warm it up until it
reaches operating temperature. The resistance
should be lower (typically 270 to 400 ohms).
Note: If restricted access to the coolant
temperature sensor makes it difficult to attach
electrical probes to the terminals, remove the
sensor as described below, and perform the
tests in a container of heated water to simulate
the conditions.
Warning: Wait until the engine is
completely cool before beginning
this procedure.
Renewal
3To remove the sensor, depress the spring
lock, unplug the electrical connector, then
carefully unscrew the sensor. Be prepared for
some coolant spillage; to reduce this, have
the new sensor ready for fitting as quickly as
possible.Caution: Handle the coolant
sensor with care. Damage to this
sensor will affect the operation of
the entire fuel injection system.
Note: It may be necessary to drain a small
amount of coolant from the radiator before
removing the sensor.
4Before the sensor is fitted, ensure its
threads are clean, and apply a little sealant to
them.
5Refitting is the reverse of removal.
Oxygen sensor
General description
Note:Oxygen sensors are normally only fitted
to those vehicles equipped with a catalytic
converter. Most oxygen sensors are located in
the exhaust pipe, downstream from the
exhaust manifold. On 535 models, the oxygen
sensor is mounted in the catalytic converter.
The sensor’s electrical connector is located
near the bulkhead (left side) for easy access.
6The oxygen sensor, which is located in the
exhaust system (see illustration), monitors
the oxygen content of the exhaust gas. The
oxygen content in the exhaust reacts with the
oxygen sensor, to produce a voltage output
which varies from 0.1 volts (high oxygen, lean
mixture) to 0.9 volts (low oxygen, rich
mixture). The ECU constantly monitors this
variable voltage output to determine the ratio
of oxygen to fuel in the mixture. The ECU
alters the air/fuel mixture ratio by controlling
the pulse width (open time) of the fuel
injectors. A mixture ratio of 14.7 parts air to 1
part fuel is the ideal mixture ratio for
minimising exhaust emissions, thus allowing
the catalytic converter to operate at maximum
efficiency. It is this ratio of 14.7 to 1 which the
ECU and the oxygen sensor attempt to
maintain at all times.
7The oxygen sensor produces no voltage
when it is below its normal operating
temperature of about 320º C. During this initial
period before warm-up, the ECU operates in
“open-loop” mode (ie without the information
from the sensor).
8If the engine reaches normal operating
temperature and/or has been running for two
or more minutes, and if the oxygen sensor is
producing a steady signal voltage below 0.45 volts at 1500 rpm or greater, the ECU
fault code memory will be activated.
9When there is a problem with the oxygen
sensor or its circuit, the ECU operates in the
“open-loop” mode - that is, it controls fuel
delivery in accordance with a programmed
default value instead of with feedback
information from the oxygen sensor.
10The proper operation of the oxygen
sensor depends on four conditions:
a) Electrical - The low voltages generated by
the sensor depend upon good, clean
connections, which should be checked
whenever a malfunction of the sensor is
suspected or indicated.
b) Outside air supply - The sensor is
designed to allow air circulation to the
internal portion of the sensor. Whenever
the sensor is disturbed, make sure the air
passages are not restricted.
c) Proper operating temperature - The ECU
will not react to the sensor signal until the
sensor reaches approximately 320º C.
This factor must be taken into
consideration when evaluating the
performance of the sensor.
d) Unleaded fuel - The use of unleaded fuel
is essential for proper operation of the
sensor. Make sure the fuel you are using
is of this type.
11In addition to observing the above
conditions, special care must be taken
whenever the sensor is serviced.
a) The oxygen sensor has a permanently-
attached pigtail and electrical connector,
which should not be removed from the
sensor. Damage or removal of the pigtail
or electrical connector can adversely
affect operation of the sensor.
b) Grease, dirt and other contaminants
should be kept away from the electrical
connector and the louvered end of the
sensor.
c) Do not use cleaning solvents of any kind
on the oxygen sensor.
d) Do not drop or roughly handle the sensor.
e) The silicone boot must be fitted in the
correct position, to prevent the boot from
being melted and to allow the sensor to
operate properly.
6•2 Engine management and emission control systems
4.6 The oxygen sensor (arrowed) is usually
located in the exhaust pipe, downstream
from the exhaust manifold4.2 Check the resistance of the coolant
temperature sensor at different
temperatures4.1 The coolant temperature sensor
(arrowed) is usually located next to the
temperature sender unit, near the fuel
pressure regulator

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

REF•23
REF
Glossary of Technical Terms
JJump startStarting the engine of a vehicle
with a discharged or weak battery by
attaching jump leads from the weak battery to
a charged or helper battery.
LLoad Sensing Proportioning Valve (LSPV)A
brake hydraulic system control valve that
works like a proportioning valve, but also
takes into consideration the amount of weight
carried by the rear axle.
LocknutA nut used to lock an adjustment
nut, or other threaded component, in place.
For example, a locknut is employed to keep
the adjusting nut on the rocker arm in
position.
LockwasherA form of washer designed to
prevent an attaching nut from working loose.
MMacPherson strutA type of front
suspension system devised by Earle
MacPherson at Ford of England. In its original
form, a simple lateral link with the anti-roll bar
creates the lower control arm. A long strut - an
integral coil spring and shock absorber - is
mounted between the body and the steering
knuckle. Many modern so-called MacPherson
strut systems use a conventional lower A-arm
and don’t rely on the anti-roll bar for location.
MultimeterAn electrical test instrument with
the capability to measure voltage, current and
resistance.
NNOxOxides of Nitrogen. A common toxic
pollutant emitted by petrol and diesel engines
at higher temperatures.
OOhmThe unit of electrical resistance. One
volt applied to a resistance of one ohm will
produce a current of one amp.
OhmmeterAn instrument for measuring
electrical resistance.
O-ringA type of sealing ring made of a
special rubber-like material; in use, the O-ring
is compressed into a groove to provide the
sealing action.Overhead cam (ohc) engineAn engine with
the camshaft(s) located on top of the cylinder
head(s).
Overhead valve (ohv) engineAn engine with
the valves located in the cylinder head, but
with the camshaft located in the engine block.
Oxygen sensorA device installed in the
engine exhaust manifold, which senses the
oxygen content in the exhaust and converts
this information into an electric current. Also
called a Lambda sensor.
PPhillips screwA type of screw head having a
cross instead of a slot for a corresponding
type of screwdriver.
PlastigageA thin strip of plastic thread,
available in different sizes, used for measuring
clearances. For example, a strip of Plastigage
is laid across a bearing journal. The parts are
assembled and dismantled; the width of the
crushed strip indicates the clearance between
journal and bearing.
Propeller shaftThe long hollow tube with
universal joints at both ends that carries
power from the transmission to the differential
on front-engined rear wheel drive vehicles.
Proportioning valveA hydraulic control
valve which limits the amount of pressure to
the rear brakes during panic stops to prevent
wheel lock-up.
RRack-and-pinion steeringA steering system
with a pinion gear on the end of the steering
shaft that mates with a rack (think of a geared
wheel opened up and laid flat). When the
steering wheel is turned, the pinion turns,
moving the rack to the left or right. This
movement is transmitted through the track
rods to the steering arms at the wheels.
RadiatorA liquid-to-air heat transfer device
designed to reduce the temperature of the
coolant in an internal combustion engine
cooling system.
RefrigerantAny substance used as a heat
transfer agent in an air-conditioning system.
R-12 has been the principle refrigerant for
many years; recently, however, manufacturers
have begun using R-134a, a non-CFC
substance that is considered less harmful tothe ozone in the upper atmosphere.
Rocker armA lever arm that rocks on a shaft
or pivots on a stud. In an overhead valve
engine, the rocker arm converts the upward
movement of the pushrod into a downward
movement to open a valve.
RotorIn a distributor, the rotating device
inside the cap that connects the centre
electrode and the outer terminals as it turns,
distributing the high voltage from the coil
secondary winding to the proper spark plug.
Also, that part of an alternator which rotates
inside the stator. Also, the rotating assembly
of a turbocharger, including the compressor
wheel, shaft and turbine wheel.
RunoutThe amount of wobble (in-and-out
movement) of a gear or wheel as it’s rotated.
The amount a shaft rotates “out-of-true.” The
out-of-round condition of a rotating part.
SSealantA liquid or paste used to prevent
leakage at a joint. Sometimes used in
conjunction with a gasket.
Sealed beam lampAn older headlight design
which integrates the reflector, lens and
filaments into a hermetically-sealed one-piece
unit. When a filament burns out or the lens
cracks, the entire unit is simply replaced.
Serpentine drivebeltA single, long, wide
accessory drivebelt that’s used on some
newer vehicles to drive all the accessories,
instead of a series of smaller, shorter belts.
Serpentine drivebelts are usually tensioned by
an automatic tensioner.
ShimThin spacer, commonly used to adjust
the clearance or relative positions between
two parts. For example, shims inserted into or
under bucket tappets control valve
clearances. Clearance is adjusted by
changing the thickness of the shim.
Slide hammerA special puller that screws
into or hooks onto a component such as a
shaft or bearing; a heavy sliding handle on the
shaft bottoms against the end of the shaft to
knock the component free.
SprocketA tooth or projection on the
periphery of a wheel, shaped to engage with a
chain or drivebelt. Commonly used to refer to
the sprocket wheel itself.
Starter inhibitor switchOn vehicles with an
O-ring
Serpentine drivebelt
Plastigage