Warm up BMW 5 SERIES 1991 E34 Owner's Manual

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

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

Check
12Warm up the engine, and let it run at idle.
Disconnect the oxygen sensor electrical
connector, and connect the positive probe of
a voltmeter to the oxygen sensor output
connector terminal (refer to the following
table) and the negative probe to earth (see
illustrations).
Note:Most oxygen sensor electrical
connectors are located at the rear of the
engine, near the bulkhead. Look for a large
rubber boot attached to a thick wire harness.
On early 535i models, the connector for the
oxygen sensor heater circuit is under the
vehicle. Look for a small protective cover.
These models should have the updated
oxygen sensor fitted, to make access similar
to other models. Consult your dealer service
department for additional information.
13Increase and then decrease the engine
speed, and monitor the voltage.
14When the speed is increased, the voltage
should increase to 0.5 to 1.0 volts. When the
speed is decreased, the voltage should fall to
about 0 to 0.4 volts.
15Also where applicable, inspect the oxygen
sensor heater (models with multi-wire
sensors). With the ignition on, disconnect the
oxygen sensor electrical connector, and
connect a voltmeter across the terminals
designated in the chart (see below). There
should be battery voltage (approximately
12 volts).
16If the reading is not correct, check the
oxygen sensor heater relay (see Chapter 12).
If the information is not available, check the
owner’s handbook for the exact location of
the oxygen sensor heater relay. The relay
should receive battery voltage.
17If the oxygen sensor fails any of these
tests, renew it.
Renewal
Note: Because it is fitted in the exhaust
manifold, converter or pipe, which contracts
when cool, the oxygen sensor may be very
difficult to loosen when the engine is cold.
Rather than risk damage to the sensor(assuming you are planning to re-use it in
another manifold or pipe), start and run the
engine for a minute or two, then switch it off.
Be careful not to burn yourself during the
following procedure.
18Disconnect 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.
19Raise and support the vehicle.
20Disconnect the electrical connector from
the sensor.
21Carefully unscrew the sensor.
Caution: Excessive force may
damage the threads.
22A high-temperature anti-seize compound
must be used on the threads of the sensor, to
facilitate future removal. The threads of new
sensors will already be coated with this
compound, but if an old sensor is removed
and refitted, recoat the threads.23Refit the sensor and tighten it securely.
24Reconnect the electrical connector of the
pigtail lead to the main engine wiring harness.
25Lower the vehicle, and reconnect the
battery.
Oxygen Sensor Heated power
sensor type output signal supply (12V)
Unheated
(single-wire) black wire (+) Not applicable
Heated terminal 1 (+) terminals
(three-wire) 3 (+) and 2 (-)
Heated terminal 2 (+) terminals
(four-wire) 4 (+) and 3 (-)
Throttle Position Sensor (TPS)
General description
26The Throttle Position Sensor (TPS) is
located on the end of the throttle shaft on the
throttle body. By monitoring the output
voltage from the TPS, the ECU can determine
fuel delivery based on throttle valve angle
(driver demand). In this system, the TPS acts
as a switch rather than a potentiometer. One
set of throttle valve switch contacts is closed
(continuity) only at idle. A second set of
contacts closes as the engine approaches
full-throttle. Both sets of contacts are open
(no continuity) between these positions. A
broken or loose TPS can cause intermittent
bursts of fuel from the injector and an
unstable idle, because the ECU thinks the
throttle is moving.
27All models (except for early 535i models
with automatic transmission) combine the idle
and full-throttle switch; a separate idle
position switch indicates the closed-throttle
position, while the TPS is used for the full-
throttle position. On 535i models with
automatic transmission, the TPS is connected
directly to the automatic transmission control
unit. With the throttle fully open, the
transmission control unit sends the full-
throttle signal to the Motronic control unit.
All models except early 535i with
automatic transmission
Check
28Remove the electrical connector from the
TPS, and connect an ohmmeter to terminals 2
and 18 (see illustrations). Open the throttle
Engine management and emission control systems 6•3
4.12b These oxygen sensor terminal
designations are for the harness side only.
Use the corresponding terminals on the
sensor side for the testing procedures
(there are three different four-wire oxygen
sensor connectors available - don’t get
them mixed up)4.12a The oxygen sensor, once it is
warmed up (320º C), puts out a very small
voltage signal. To verify it is working,
check for voltage with a digital voltmeter
(the voltage signals usually range from
0.1 to 1.0 volt)
4.28b First check for continuity between
terminals 2 and 18 with the throttle closed
(later Motronic system shown) . . .4.28a The TPS on L-Jetronic systems is
located under the intake manifold
(terminals arrowed)
6

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

it to the approximate size and shape required,
then pull off the backing paper (if used) and
stick the tape over the hole; it can be
overlapped if the thickness of one piece is
insufficient. Burnish down the edges of the
tape with the handle of a screwdriver or
similar, to ensure that the tape is securely
attached to the metal underneath.
Bodywork repairs - filling and
respraying
Before using this Section, see the Sections
on dent, deep scratch, rust holes and gash
repairs.
Many types of bodyfiller are available, but
generally speaking, those proprietary kits
which contain a tin of filler paste and a tube of
resin hardener are best for this type of repair. A
wide, flexible plastic or nylon applicator will be
found invaluable for imparting a smooth and
well-contoured finish to the surface of the filler.
Mix up a little filler on a clean piece of card
or board - measure the hardener carefully
(follow the maker’s instructions on the pack),
otherwise the filler will set too rapidly or too
slowly. Using the applicator, apply the filler
paste to the prepared area; draw the
applicator across the surface of the filler to
achieve the correct contour and to level the
surface. As soon as a contour that
approximates to the correct one is achieved,
stop working the paste - if you carry on too
long, the paste will become sticky and begin
to “pick-up” on the applicator. Continue to
add thin layers of filler paste at 20-minute
intervals, until the level of the filler is just
proud of the surrounding bodywork.
Once the filler has hardened, the excess
can be removed using a metal plane or file.
From then on, progressively-finer grades of
abrasive paper should be used, starting with a
40-grade production paper, and finishing with
a 400-grade wet-and-dry paper. Always wrap
the abrasive paper around a flat rubber, cork,
or wooden block - otherwise the surface of
the filler will not be completely flat. During the
smoothing of the filler surface, the wet-and-
dry paper should be periodically rinsed in
water. This will ensure that a very smooth
finish is imparted to the filler at the final stage.
At this stage, the “dent” should be
surrounded by a ring of bare metal, which in
turn should be encircled by the finely
“feathered” edge of the good paintwork.
Rinse the repair area with clean water, until all
of the dust produced by the rubbing-down
operation has gone.
Spray the whole area with a light coat of
primer - this will show up any imperfections in
the surface of the filler. Repair these
imperfections with fresh filler paste or
bodystopper, and once more smooth the
surface with abrasive paper. Repeat this
spray-and-repair procedure until you are
satisfied that the surface of the filler, and the
feathered edge of the paintwork, are perfect.
Clean the repair area with clean water, and
allow to dry fully.The repair area is now ready for final
spraying. Paint spraying must be carried out
in a warm, dry, windless and dust-free
atmosphere. This condition can be created
artificially if you have access to a large indoor
working area, but if you are forced to work in
the open, you will have to pick your day very
carefully. If you are working indoors, dousing
the floor in the work area with water will help
to settle the dust which would otherwise be in
the atmosphere. If the repair area is confined
to one body panel, mask off the surrounding
panels; this will help to minimise the effects of
a slight mis-match in paint colours. Bodywork
fittings (eg chrome strips, door handles etc)
will also need to be masked off. Use genuine
masking tape, and several thicknesses of
newspaper, for the masking operations.
Before commencing to spray, agitate the
aerosol can thoroughly, then spray a test area
(an old tin, or similar) until the technique is
mastered. Cover the repair area with a thick
coat of primer; the thickness should be built
up using several thin layers of paint, rather
than one thick one. Using 400-grade wet-and-
dry paper, rub down the surface of the primer
until it is really smooth. While doing this, the
work area should be thoroughly doused with
water, and the wet-and-dry paper periodically
rinsed in water. Allow to dry before spraying
on more paint.
Spray on the top coat, again building up the
thickness by using several thin layers of paint.
Start spraying at one edge of the repair area,
and then, using a side-to-side motion, work
until the whole repair area and about 2 inches
of the surrounding original paintwork is
covered. Remove all masking material 10 to
15 minutes after spraying on the final coat of
paint.
Allow the new paint at least two weeks to
harden, then, using a paintwork renovator, or
a very fine cutting paste, blend the edges of
the paint into the existing paintwork. Finally,
apply wax polish.
Plastic components
With the use of more and more plastic body
components by the vehicle manufacturers (eg
bumpers. spoilers, and in some cases major
body panels), rectification of more serious
damage to such items has become a matter
of either entrusting repair work to a specialist
in this field, or renewing complete
components. Repair of such damage by the
DIY owner is not really feasible, owing to the
cost of the equipment and materials required
for effecting such repairs. The basic technique
involves making a groove along the line of the
crack in the plastic, using a rotary burr in a
power drill. The damaged part is then weldedback together, using a hot-air gun to heat up
and fuse a plastic filler rod into the groove.
Any excess plastic is then removed, and the
area rubbed down to a smooth finish. It is
important that a filler rod of the correct plastic
is used, as body components can be made of
a variety of different types (eg polycarbonate,
ABS, polypropylene).
Damage of a less serious nature (abrasions,
minor cracks etc) can be repaired by the DIY
owner using a two-part epoxy filler repair
material. Once mixed in equal proportions,
this is used in similar fashion to the bodywork
filler used on metal panels. The filler is usually
cured in twenty to thirty minutes, ready for
sanding and painting.
If the owner is renewing a complete
component himself, or if he has repaired it
with epoxy filler, he will be left with the
problem of finding a suitable paint for finishing
which is compatible with the type of plastic
used. At one time, the use of a universal paint
was not possible, owing to the complex range
of plastics encountered in body component
applications. Standard paints, generally
speaking, will not bond to plastic or rubber
satisfactorily. However, it is now possible to
obtain a plastic body parts finishing kit which
consists of a pre-primer treatment, a primer
and coloured top coat. Full instructions are
normally supplied with a kit, but basically, the
method of use is to first apply the pre-primer
to the component concerned, and allow it to
dry for up to 30 minutes. Then the primer is
applied, and left to dry for about an hour
before finally applying the special-coloured
top coat. The result is a correctly-coloured
component, where the paint will flex with the
plastic or rubber, a property that standard
paint does not normally possess.
6 Bodywork repair-
major damage
5
1Major damage must be repaired by a
qualified bodywork repair specialist, or
preferably by a BMW dealer. Specialised
equipment is required to do the job properly.
2If the damage is extensive, the bodyshell
must be checked for proper alignment, or the
vehicle’s handling characteristics may be
adversely affected and other components
may wear at an accelerated rate.
3Due to the fact that all of the major body
components (bonnet, wings, etc.) are
separate units, any seriously damaged
components should be replaced with new
ones rather than repaired.
Bodywork and fittings 11•3
11
If bodystopper is used, it can
be mixed with cellulose
thinners to form a really thin
paste which is ideal for filling
small holes
Sometimes bodywork
components can be found in
a scrapyard that specialises
in used vehicle components,
often at a considerable saving over the
cost of new parts.