ignition wiring BMW 5 SERIES 1988 E34 Workshop Manual
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Page 6 of 228
0•6Safety First!
Working on your car can be dangerous.
This page shows just some of the potential
risks and hazards, with the aim of creating a
safety-conscious attitude.
General hazards
Scalding
• Don’t remove the radiator or expansion
tank cap while the engine is hot.
• Engine oil, automatic transmission fluid or
power steering fluid may also be dangerously
hot if the engine has recently been running.
Burning
• Beware of burns from the exhaust system
and from any part of the engine. Brake discs
and drums can also be extremely hot
immediately after use.
Crushing
• When working under or near
a raised vehicle,
always
supplement the
jack with axle
stands, or use
drive-on
ramps.
Never
venture
under a car which
is only supported by a jack.
• Take care if loosening or tightening high-
torque nuts when the vehicle is on stands.
Initial loosening and final tightening should
be done with the wheels on the ground.
Fire
• Fuel is highly flammable; fuel vapour is
explosive.
• Don’t let fuel spill onto a hot engine.
• Do not smoke or allow naked lights
(including pilot lights) anywhere near a
vehicle being worked on. Also beware of
creating sparks
(electrically or by use of tools).
• Fuel vapour is heavier than air, so don’t
work on the fuel system with the vehicle over
an inspection pit.
• Another cause of fire is an electrical
overload or short-circuit. Take care when
repairing or modifying the vehicle wiring.
• Keep a fire extinguisher handy, of a type
suitable for use on fuel and electrical fires.
Electric shock
• Ignition HT
voltage can be
dangerous,
especially to
people with heart
problems or a
pacemaker. Don’t
work on or near the
ignition system with
the engine running or
the ignition switched on.• Mains voltage is also dangerous. Make
sure that any mains-operated equipment is
correctly earthed. Mains power points should
be protected by a residual current device
(RCD) circuit breaker.
Fume or gas intoxication
• Exhaust fumes are
poisonous; they often
contain carbon
monoxide, which is
rapidly fatal if inhaled.
Never run the
engine in a
confined space
such as a garage
with the doors shut.
• Fuel vapour is also
poisonous, as are the vapours from some
cleaning solvents and paint thinners.
Poisonous or irritant substances
• Avoid skin contact with battery acid and
with any fuel, fluid or lubricant, especially
antifreeze, brake hydraulic fluid and Diesel
fuel. Don’t syphon them by mouth. If such a
substance is swallowed or gets into the eyes,
seek medical advice.
• Prolonged contact with used engine oil can
cause skin cancer. Wear gloves or use a
barrier cream if necessary. Change out of oil-
soaked clothes and do not keep oily rags in
your pocket.
• Air conditioning refrigerant forms a
poisonous gas if exposed to a naked flame
(including a cigarette). It can also cause skin
burns on contact.
Asbestos
• Asbestos dust can cause cancer if inhaled
or swallowed. Asbestos may be found in
gaskets and in brake and clutch linings.
When dealing with such components it is
safest to assume that they contain asbestos.
Special hazards
Hydrofluoric acid
• This extremely corrosive acid is formed
when certain types of synthetic rubber, found
in some O-rings, oil seals, fuel hoses etc, are
exposed to temperatures above 400
0C. The
rubber changes into a charred or sticky
substance containing the acid. Once formed,
the acid remains dangerous for years. If it
gets onto the skin, it may be necessary to
amputate the limb concerned.
• When dealing with a vehicle which has
suffered a fire, or with components salvaged
from such a vehicle, wear protective gloves
and discard them after use.
The battery
• Batteries contain sulphuric acid, which
attacks clothing, eyes and skin. Take care
when topping-up or carrying the battery.
• The hydrogen gas given off by the battery
is highly explosive. Never cause a spark or
allow a naked light nearby. Be careful when
connecting and disconnecting battery
chargers or jump leads.
Air bags
• Air bags can cause injury if they go off
accidentally. Take care when removing the
steering wheel and/or facia. Special storage
instructions may apply.
Diesel injection equipment
• Diesel injection pumps supply fuel at very
high pressure. Take care when working on
the fuel injectors and fuel pipes.
Warning: Never expose the hands,
face or any other part of the body
to injector spray; the fuel can
penetrate the skin with potentially fatal
results.
Remember...
DO
• Do use eye protection when using power
tools, and when working under the vehicle.
• Do wear gloves or use barrier cream to
protect your hands when necessary.
• Do get someone to check periodically
that all is well when working alone on the
vehicle.
• Do keep loose clothing and long hair well
out of the way of moving mechanical parts.
• Do remove rings, wristwatch etc, before
working on the vehicle – especially the
electrical system.
• Do ensure that any lifting or jacking
equipment has a safe working load rating
adequate for the job.
A few tips
DON’T
• Don’t attempt to lift a heavy component
which may be beyond your capability – get
assistance.
• Don’t rush to finish a job, or take
unverified short cuts.
• Don’t use ill-fitting tools which may slip
and cause injury.
• Don’t leave tools or parts lying around
where someone can trip over them. Mop
up oil and fuel spills at once.
• Don’t allow children or pets to play in or
near a vehicle being worked on.
Page 9 of 228
0•9Roadside Repairs
When jump-starting a car using a
booster battery, observe the following
precautions:
4Before connecting the booster
battery, make sure that the ignition is
switched off.
4Ensure that all electrical equipment
(lights, heater, wipers, etc) is
switched off.
4Make sure that the booster battery is
the same voltage as the discharged
one in the vehicle.
4If the battery is being jump-started
from the battery in another vehicle,
the two vehcles MUST NOT TOUCH
each other.
4Make sure that the transmission is in
neutral (or PARK, in the case of
automatic transmission).
Jump starting will get you out
of trouble, but you must correct
whatever made the battery go
flat in the first place. There are
three possibilities:
1The battery has been drained by
repeated attempts to start, or by
leaving the lights on.
2The charging system is not working
properly (alternator drivebelt slack
or broken, alternator wiring fault or
alternator itself faulty).
3The battery itself is at fault
(electrolyte low, or battery worn out).
Connect one end of the red jump lead to
the positive (+) terminal of the flat
batteryConnect the other end of the red lead to
the positive (+) terminal of the booster
battery.Connect one end of the black jump lead
to the negative (-) terminal of the
booster battery
Connect the other end of the black
jump lead to a bolt or bracket on the
engine block, well away from the
battery, on the vehicle to be started.
123
4
Make sure that the jump leads will not
come into contact with the fan, drive-
belts or other moving parts of the
engine.5
Start the engine using the booster
battery, then with the engine running at
idle speed, disconnect the jump leads in
the reverse order of connection.6
Jump starting
Page 25 of 228
move the component away from the engine to
tighten the belt, or towards the engine to
loosen the belt. Hold the accessory in
position, and check the belt tension. If it is
correct, tighten the two bolts until just tight,
then recheck the tension. If the tension is still
correct, tighten the bolts.
8It will often be necessary to use some sort
of lever to move the accessory while the belt
is adjusted. If this must be done to gain the
proper leverage, be very careful not to
damage the component being moved, or the
part being prised against.
Renewal
9To renew a belt, follow the instructions
above for adjustment, but remove the belt
from the pulleys.
10In some cases, you will have to remove
more than one belt, because of their
arrangement on the front of the engine.
Because of this, and the fact that belts will
tend to fail at the same time, it is wise to
renew all belts together. Mark each belt and
its appropriate pulley groove, so all renewed
belts can be fitted in their proper positions.
11It is a good idea to take the old belts with
you when buying new ones, in order to make
a direct comparison for length, width and
design.
12Recheck the tension of new belts after a
few hundred miles.
12 Engine idle speed and CO
level check and adjustment
4
Note:The engine should be at normal
operating temperature, with correct ignition
timing and valve clearances (where
adjustable). The air filter should be in good
condition, and all electrical components
(including the air conditioning, where fitted)
should be switched off.
Carburettor
1Connect a tachometer and exhaust gas
analyser (CO meter) to the engine.
2Start the engine and allow it to idle.
3Check that the idle speed is as given in the
Specifications. Adjustment of the idle speed is
only possible on the 2B4 carburettor. Turn the
carburettor idle speed adjustment screw until
the engine idles at the correct speed (see
illustration).
4If the idle speed is low on the 2BE
carburettor, and all wiring to the carburettor is
in good condition, it is possible to connect a
resistance into the control circuit. This should
be carried out by your BMW dealer.
5Check that the CO reading is as given in the
Specifications. If not, turn the carburettor idle
mixture adjustment screw until the mixture is
correct (see illustration).
L-Jetronic
6Connect a tachometer and CO meter to the
engine. BMW technicians use a special CO
tester with a probe connected into the
exhaust manifold, but the normal type of
tester which locates in the exhaust tailpipe
can be used instead. Note however that on
models with a catalytic converter, meaningful
CO readings will not be obtained at the
tailpipe.
7Start the engine and allow it to idle.
8Check that the idle speed is as given in
Specifications. If not, remove the tamperproof
cap from the throttle housing, and turn the idle
adjustment screw until the speed is correct.
9Check that the CO reading is as given in the
Specifications. The mixture control screw is
located on the airflow meter, and a specialtool (BMW number 13 1 060) may be required
to make the adjustment.
Motronic
10Connect a tachometer and CO meter to
the engine. BMW technicians use a special
CO tester with a probe connected into the
exhaust manifold, but the normal type of
tester which locates in the exhaust tailpipe
may be used instead. Note however that on
models with a catalytic converter, meaningful
CO readings will not be obtained at the
tailpipe.
11It is not possible to adjust the idle speed
manually, as the idle air stabiliser valve is
activated by the electronic control unit. If the
idle speed is not within the specified range
with the engine at normal operating
temperature, check for a leak in the air inlet
system, and also check the operation of the
idle air stabiliser valve (see Chapter 4).
12Check that the CO reading is as given in
the Specifications. If adjustment is required,
prise out the tamperproof plug from the
airflow meter, and turn the adjustment screw
to set the CO content (on some models, an
Allen key will be required). Fit a new
tamperproof plug on completion (see
illustrations).
1•15
12.12a Removing the tamperproof plug
from the airflow meter
12.5 Mixture adjustment screw (2) on the
2B4 carburettor
12.3 Idle speed adjustment screw on the
2B4 carburettor (shown with the
carburettor removed)
12.12b Adjusting the CO on the Motronic
system
1
Every 6000 miles
Page 49 of 228
22Using a scraper, remove all traces of old
gasket material from the sealing surfaces of
the covers and engine block.
Caution: Be very careful not to
scratch or gouge the delicate
aluminium surfaces. Also, do not
damage the sump gasket, and
keep it clean. 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.
23Support the cover on two blocks of wood,
and drive out the seals from behind with a
hammer and screwdriver. Be very careful not
to damage the seal bores in the process.
24Coat the outside diameters and lips of the
new seals with multi-purpose grease, and
drive the seals into the cover with a hammer
and a socket slightly smaller in diameter than
the outside diameter of the seal.
25Apply a film of RTV-type gasket sealant to
the surface of the sump gasket that mates
with the front cover. Apply extra beads of RTV
sealant to the edges where the gasket meets
the engine block. Note:If the sump gasket is
damaged, instead of fitting a whole new
gasket, you might try trimming the front
portion of the gasket off at the point where it
meets the engine block, then trim off the front
portion of a new sump gasket so it’s exactly
the same size. Cover the exposed inside area
of the sump with a rag, then clean all traces of
old gasket material off the area where the
gasket was removed. Attach the new gasket
piece to the sump with contact-cement-type
gasket adhesive, then apply RTV-type sealant
as described at the beginning of this
paragraph.
26Coat both sides of the new gasket with
RTV-type gasket sealant, then attach the front
cover to the front of the engine, carefully
working the seals over the crankshaft and
intermediate shaft. Refit the bolts and tighten
them evenly to the torque listed in this
Chapter’s Specifications. Work from bolt-to-
bolt in a criss-cross pattern, to be sure they’re
tightened evenly.Note 1:Tighten the front
cover-to-block bolts first, then tighten the
sump-to-cover bolts. Note 2:After applying
RTV-type sealant, reassembly must be
completed in about 10 minutes so the RTV
won’t prematurely harden.
27The remainder of refitting is the reverse of
removal.
Crankshaft front seal (M40 engines)
28Remove the timing belt and crankshaft
sprocket (see Section 10).
29Remove the Woodruff key from the
groove in the end of the crankshaft.
30Note the fitted position of the oil seal, then
prise it out from the front cover using a
screwdriver, but take care not to damage the
bore of the cover or the surface of thecrankshaft. If the seal is tight, drill two small
holes in the metal end of the seal, and use two
self-tapping screws to pull out the seal. Make
sure all remains of swarf are removed.
31Coat the outside diameter and lip of the
new seal with multi-purpose grease, then
drive it into the cover with a hammer and a
socket slightly smaller in diameter than the
outside diameter of the seal. Make sure the
seal enters squarely.
32The remainder of refitting is the reverse of
removal. Note that it is recommended that the
timing belt be renewed - see Section 10.
12 Cylinder head-
removal and refitting
5
Removal
1Relieve the fuel pressure on all fuel injection
engines (see Chapter 4).
2Disconnect the negative cable from the
battery. Where the battery is located in the
engine compartment, the battery may be
removed completely (see Chapter 5).
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.
3Remove the air cleaner assembly (see
Chapter 4).
4Disconnect the wiring from the distributor
(mark all wiring for position first, if necessary),
and the HT lead from the coil (see Chapter 5).
5Disconnect the lead from the coolant
temperature sender unit (see Chapter 3).
6Disconnect the fuel lines from the fuel rail or
carburettor as applicable (see Chapter 4).
7Drain the cooling system (see Chapter 3).
8Clearly label then disconnect all other
hoses from the throttle body, intake manifold,
carburettor and cylinder head, as applicable.
9Disconnect the throttle cable from the
throttle linkage or carburettor (see Chapter 4).
10Disconnect the exhaust manifold from the
cylinder head (see Section 6). Depending on
the engine type, It may not be necessary to
disconnect the manifold from the exhaust
pipe; however, on right-hand-drive models,
the steering column intermediate shaft may
not allow the manifold to clear the studs on
the cylinder head.
11Remove or disconnect any remaining
hoses or lines from the intake manifold,
including the ignition advance vacuum line(s),
and the coolant and heater hoses.
12On early carburettor models, disconnect
the wiring from the alternator and starter
motor.13Remove the intake manifold (see Sec-
tion 5). Do not dismantle or remove any fuel
injection system components unless it is
absolutely necessary.
14Remove the fan drivebelt and fan (see
Chapter 3).
15Remove the valve cover and gasket (see
Section 4). Remove the semi-circular rubber
seal from the front of the cylinder head, where
this is not incorporated in the valve cover
gasket.
16Set No 1 piston at Top Dead Centre on
the compression stroke (see Section 3).
17Remove the timing chain or belt (see
Section 8 or 10). Note:If you want to save
time by not removing and refitting the timing
belt or chain and re-timing the engine, you can
unfasten the camshaft sprocket and suspend
it out of the way - with the belt or chain still
attached - by a piece of rope. Be sure the
rope keeps firm tension on the belt or chain,
so it won’t become disengaged from any of
the sprockets.
18Loosen the cylinder head bolts a quarter-
turn at a time each, in the reverse of the
tightening sequence shown (see illustrations
12.30a, 12.30b, 12.30c or 12.30d). Do
notdismantle or remove the rocker arm
assembly at this time on M10, M20 and M30
engines.
19Remove the cylinder head by lifting it
straight up and off the engine block. Do not
prise between the cylinder head and the
engine block, as damage to the gasket sealing
surfaces may result. Instead, use a blunt bar
positioned in an intake port to gently prise the
head loose.
20Remove any remaining external
components from the head to allow for
thorough cleaning and inspection. See
Chapter 2B for cylinder head servicing
procedures. On the M40 engine, remove the
rubber O-ring from the groove in the top of the
oil pump/front end cover housing.
Refitting
21The mating surfaces of the cylinder head
and block must be perfectly clean when the
head is refitted.
22Use a gasket scraper to remove all traces
of carbon and old gasket material, then clean
the mating surfaces with a suitable solvent. If
there’s oil on the mating surfaces when the
head is refitted, the gasket may not seal
correctly, and leaks could develop. When
working on the block, stuff the cylinders with
clean rags to keep out debris. Use a vacuum
cleaner to remove material that falls into the
cylinders.
23Check the block and head mating
surfaces for nicks, deep scratches and other
damage. If the damage is slight, it can be
removed with a file; if it’s excessive,
machining may be the only alternative.
24Use a tap of the correct size to chase the
threads in the head bolt holes, then clean the
holes with compressed air - make sure that
In-car engine repair procedures 2A•13
2A
Page 61 of 228
otherwise a small brush or even a bicycle tyre
pump will work). The idea is to prevent dirt
from getting into the cylinders as the
compression check is being done.
3Remove all the spark plugs from the engine
(see Chapter 1).
4Block the throttle wide open, or have an
assistant hold the throttle pedal down.
5On carburettor models, disconnect the LT
lead from the coil. On fuel injection models,
disable the fuel pump and ignition circuit by
removing the main relay(see illustration).
This is to avoid the possibility of a fire from
fuel being sprayed in the engine
compartment. The location of the main relay is
generally near the fuse panel area under the
bonnet, but refer to Chapter 12 for the
specific location on your model.
6Fit the compression gauge in the No 1
spark plug hole (No 1 cylinder is nearest the
radiator).
7Turn the engine on the starter motor over at
least seven compression strokes, and watch
the gauge. The compression should build up
quickly in a healthy engine. Low compression
on the first stroke, followed by gradually-
increasing pressure on successive strokes,
indicates worn piston rings. A low
compression reading on the first stroke, which
doesn’t build up during successive strokes,
indicates leaking valves or a blown head
gasket (a cracked head could also be the
cause). Deposits on the undersides of the
valve heads can also cause low compression.
Record the highest gauge reading obtained.
8Repeat the procedure for the remaining
cylinders, and compare the results to the
compression listed in this Chapter’s Specifi-
cations.
9If compression was low, add some engine
oil (about three squirts from a plunger-type oil
can) to each cylinder, through the spark plug
hole, and repeat the test.
10If the compression increases after the oil
is added, the piston rings are definitely worn.
If the compression doesn’t increasesignificantly, the leakage is occurring at the
valves or head gasket. Leakage past the
valves may be caused by burned valve seats
and/or faces or warped, cracked or bent
valves.
11If two adjacent cylinders have equally low
compression, there’s a strong possibility that
the head gasket between them is blown. The
appearance of coolant in the combustion
chambers or the crankcase would verify this
condition.
12If one cylinder is 20 percent lower than the
others, and the engine has a slightly rough
idle, a worn exhaust lobe on the camshaft
could be the cause.
13If the compression is unusually high, the
combustion chambers are probably coated
with carbon deposits. If that’s the case, the
cylinder head should be removed and
decarbonised.
14If compression is way down, or varies
greatly between cylinders, it would be a good
idea to have a leak-down test performed by a
garage. This test will pinpoint exactly
where the leakage is occurring and how
severe it is.
4 Engine removal-
methods and precautions
If you’ve decided that an engine must be
removed for overhaul or major repair work,
several preliminary steps should be taken.
Locating a suitable place to work is
extremely important. Adequate work space,
along with storage space for the vehicle, will
be needed. If a workshop or garage isn’t
available, at the very least a flat, level, clean
work surface made of concrete or asphalt is
required.
Cleaning the engine compartment and
engine before beginning the removal
procedure will help keep tools clean and
organised.
An engine hoist or A-frame will also be
necessary. Make sure the equipment is rated
in excess of the combined weight of the
engine and accessories. Safety is of primary
importance, considering the potential hazards
involved in lifting the engine out of the vehicle.
If the engine is being removed by a novice,
a helper should be available. Advice and aid
from someone more experienced would also
be helpful. There are many instances when
one person cannot simultaneously perform all
of the operations required when lifting the
engine out of the vehicle.
Plan the operation ahead of time. Arrange
for or obtain all the tools and equipment you’ll
need prior to beginning the job. Some of the
equipment necessary to perform engine
removal and refitting safely and with relative
ease are (in addition to an engine hoist) a
heavy-duty trolley jack, complete sets of
spanners and sockets as described in thefront of this manual, wooden blocks, and
plenty of rags and cleaning solvent for
mopping up spilled oil, coolant and fuel. If the
hoist must be hired, make sure that you
arrange for it in advance, and perform all of
the operations possible without it beforehand.
This will save you money and time.
Plan for the vehicle to be out of use for
quite a while. A machine shop will be required
to perform some of the work which the do-it-
yourselfer can’t accomplish without special
equipment. These establishments often have
a busy schedule, so it would be a good idea
to consult them before removing the engine,
in order to accurately estimate the amount of
time required to rebuild or repair components
that may need work.
Always be extremely careful when removing
and refitting the engine. Serious injury can
result from careless actions. Plan ahead, take
your time and a job of this nature, although
major, can be accomplished successfully.
Warning: The air conditioning
system is under high pressure.
Do not loosen any fittings or
remove any components until
after the system has been discharged by a
qualified engineer. Always wear eye
protection when disconnecting air
conditioning system fittings.
Caution: If removing the M40
engine, it is important not to turn
the engine upside-down for
longer than 10 minutes since it is
possible for the oil to drain out of the
hydraulic tappets. This would render the
tappets unserviceable, and damage could
possibly occur to the engine when it is
next started up.
5 Engine- removal and refitting
3
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.
Removal1Relieve the fuel system pressure (see
Chapter 4), then disconnect the negative
cable from the battery.
2Cover the wings and front panel, and
remove the bonnet (see Chapter 11). Special
pads are available to protect the wings, but an
old bedspread or blanket will also work.
3Remove the air cleaner housing and intake
ducts (see Chapter 4).
4Drain the cooling system (see Chapter 1).
5Label the vacuum lines, emissions system
hoses, wiring connectors, earth straps and
fuel lines, to ensure correct refitting, then
General engine overhaul procedures 2B•5
3.5 As a safety precaution, before
performing a compression check, remove
the cover and the main relay (arrowed)
from the left side of the engine
compartment to disable the fuel and
ignition systems (525i model shown, other
models similar)
2B
Page 82 of 228
disconnect the fluid cooler lines from the
radiator. Use a drip tray to catch spilled fluid.
Plug the fluid cooler lines and fittings.
7Disconnect the coolant sensors located on
the radiator (see illustration). The thermo-
statically-controlled switches for high- and
low-speed operation of the auxiliary fan are
located in the radiator tanks, in various
locations depending on engine and model.
8Remove the radiator mounting bolt(s). The
mountings are either on the top or sides of the
radiator (see illustration).
9Carefully lift out the radiator from the
bottom mountings, taking care not to damage
the cooling fins. Don’t spill coolant on the
vehicle, or scratch the paint.
10With the radiator removed, it can be
inspected for leaks and damage. If it needs
repair, have a specialist perform the work, as
special techniques are required.
11Flies and dirt can be removed from the
radiator with compressed air and a soft brush.
Don’t bend the cooling fins as this is done.
12Check the radiator mountings for
deterioration, and renew if necessary (see
illustration).
Refitting
13Refitting is the reverse of the removal
procedure.
14After refitting, fill the cooling system with
the proper mixture of antifreeze and water.
Refer to Chapter 1 if necessary.15Start the engine and check for leaks.
Allow the engine to reach normal operating
temperature, indicated by the upper radiator
hose becoming hot. Recheck the coolant
level, and add more if required.
16If you’re working on an automatic
transmission model, check and add
transmission fluid as needed.
5 Engine cooling fan(s) and
clutch- check, removal and
refitting
1
Warning: To avoid possible injury
or damage, DO NOT operate the
engine with a damaged fan. Do
not attempt to repair fan blades -
fit a new fan. Also, the electric auxiliary fan
in front of the radiator or air conditioning
condenser can come on without the
engine running or ignition being on. It is
controlled by the coolant temperature of
the thermo-switches located in the
radiator.
Check
Electric auxiliary fan
Note: This fan on most models is controlled
by two thermo-switches placed in the radiator:
one for low-speed/low-temperature operation,
and one for high-speed/high-temperature
operation. Each switch comes on at a different
coolant temperature (refer to the Specifica-
tions at the beginning of this Chapter).
1The thermostatically-controlled switches for
high- and low-speed operation of the auxiliary
fan are fitted in various locations in the
radiator (see illustration 4.7), depending on
engine or model. Two single switches, or one
dual switch, may be fitted.
2Insert a small screwdriver into the
connector to lift the lock tab, and unplug the
fan wire harness.
3To test the fan motor, unplug the electrical
connector at the motor, and use jumper wires
to connect the fan directly to the battery. If the
fan doesn’t work when connected directly to
the battery, the motor is proved faulty, and
must be renewed. If the fan works, there’s agood chance the switch is malfunctioning. To
more accurately diagnose the problem, follow
the steps that apply to your model. Note: Spin
the auxiliary fan motor by hand, to check that
the motor or fan isn’t binding. Make sure,
however, that the engine is sufficiently cool
that there is no danger of the fan cutting-in on
its own when this is done.
4To test the low-speed and high-speed
circuits, disconnect the electrical connector
from one of the fan switches, and bridge the
terminals of the switch’s electrical connector
with a short piece of wire. The fan should run
at low or high speed, depending on which
switch has been disconnected. On some
models the ignition must be on before the fan
will run.
5Repeat the test at the other switch so that
both high and low speeds are tested.
6If the low-speed and high-speed circuits
are OK, but there has been a problem with the
fan not operating correctly in service, renew
the switch (or switches). To remove a switch,
drain the coolant below the level of the switch
(see Chapter 1), then unscrew the switch and
screw in the new one. Refill the system with
coolant.
7If the switches are satisfactory, but the
motor still does not operate, the problem lies
in the fuse, the relay, the wiring which
connects the components (or the fan motor
itself). Carefully check the fuse, relay, all
wiring and connections. See Chapter 12 for
more information on how to carry out these
checks.
Mechanical fan with viscous clutch
8Disconnect the battery negative cable, and
rock the fan back and forth by hand to check
for excessive bearing play.
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.
9With the engine cold, turn the fan blades by
hand. The fan should turn with slight
resistance.
10Visually inspect for substantial fluid
leakage from the fan clutch assembly. If
problems are noted, renew the fan clutch
assembly.
11With the engine completely warmed up,
turn off the ignition switch and disconnect the
battery negative cable. Turn the fan by hand.
Heavier resistance should be evident. If the
fan turns easily, a new fan clutch may be
needed.
Removal and refitting
Electric auxiliary fan
12Disconnect the battery negative cable.
13To remove the auxiliary fan follow the
procedure that applies to your vehicle.
3•4 Cooling, heating and air conditioning systems
4.12 When the radiator is out, the radiator
mountings can be inspected - check for
signs of deterioration, and renew them, if
needed
4.8 The radiator is bolted to the front
panel at either the sides or the top of the
radiator4.7 Sensors that control the high- and
low-speed operation of the auxiliary
cooling fan are located in various places in
the radiator tanks
Page 84 of 228
M20 engine
9Remove the distributor cap and HT leads,
ignition rotor and dust shield (see Chapter 1).
10Where applicable, remove the timing
sensor (see Chapter 5).
11Remove the timing belt upper cover (see
Chapter 2A).
12Loosen all three water pump mounting
bolts. Remove the top and right-hand side
bolts, but DON’T remove the lower bolt (see
illustration).
13Rotate the pump downwards, and remove
the drivebelt tensioner spring and pin.
14 Remove the final water pump bolt, and
remove the pump.
Caution: Leave the tensioner bolt
tight. Be careful to not move the
camshaft gear, as damage can
occur if the valves are moved.
M30 engine
15Remove the engine lifting bracket.
16Remove the bolts that mount the water
pump to the engine block.
17Remove the water pump, and recover the
gasket.
M40 engine
18Unscrew the mounting bolts and remove
the water pump. If the pump is tight in the
cylinder head, insert two bolts in the special
lugs at the top and bottom of the pump, and
tighten them evenly to press the pump out of
the head (see illustrations).
Refitting
19Clean the bolt threads and the threaded
holes in the engine to remove corrosion and
sealant.
20Compare the new pump to the old one, to
make sure they’re identical.
21Remove all traces of old gasket material
from the engine with a gasket scraper.
22Clean the water pump mating surfaces.
23On the M40 engine, locate a new O-ring
on the pump (see illustration).
24Locate the gasket on the pump, and offer
the pump up to the engine (see illustration).
Slip a couple of bolts through the pump
mounting holes to hold the gasket in place.
25Carefully attach the pump and gasket to
the engine, threading the bolts into the holes
finger-tight.Note:On the M20 engine, refit the
lower bolt finger-tight, then rotate the water
pump into position with the drivebelt tensioner
spring and pin in position.
26Refit the remaining bolts (if they also hold
an accessory bracket in place, be sure to
reposition the bracket at this time). Tighten
them to the torque listed in this Chapter’s
Specifications, in quarter-turn increments.
Don’t overtighten them, or the pump may be
distorted.
27Refit all parts removed for access to the
pump.
28Refill the cooling system and check the
drivebelt tension (see Chapter 1). Run the
engine and check for leaks.8 Coolant temperature sender
unit- check and renewal
2
Warning: Wait until the engine is
completely cool before beginning
this procedure.
1The coolant temperature indicator system
is composed of a temperature gauge
mounted in the instrument panel, and a
coolant temperature sender unit that’s
normally mounted on the thermostat housing
(see illustration 3.11). Some vehicles have
more than one sender unit, but only one is
used for the temperature gauge. On the M40
engine, the sender unit is mounted on the left-
hand side of the cylinder head, towards the
rear.
2If the gauge reading is suspect, first check
the coolant level in the system. Make sure the
wiring between the gauge and the sending
unit is secure, and that all fuses are intact. (If
the fuel gauge reading is suspect as well, the
problem is almost certainly in the instrument
panel or its wiring.)
3Before testing the circuit, refer to the
relevant wiring diagrams (see Chapter 12).
Where the sender unit simply earths out the
circuit, test by earthing the wire connected to
the sending unit while the ignition is on (but
without the engine running, for safety). If the
gauge now deflects to the end of the scale,
renew the sender unit. If the gauge does not
respond satisfactorily, the gauge, or the wiring
to the gauge, is faulty. Where the sender unit
has two terminals, test the circuit by checking
the resistance of the unit. No figures were
available at the time of writing, but typically
readings of several hundred or several
thousand ohms (depending on temperature)
would be expected. A reading of zero (short-
circuit) or infinity (open-circuit) would indicate
a faulty sender unit.
Caution: Do not earth the wire
for more than a second or two, or
damage to the gauge could
occur.
3•6 Cooling, heating and air conditioning systems
7.24 New outer gasket on the M40 engine
water pump7.23 Fit a new O-ring on the M40 engine
water pump
7.18b . . . and remove the water pump
(M40 engine)7.18a With the water pump mounting bolts
removed, screw two bolts into the special
lugs (one top and one bottom) . . .7.12 Water pump bolt locations on the
M20 engine
Page 93 of 228
19Depressurise the fuel system (see Sec-
tion 2).
20Detach 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.
21Detach the fuel feed hose from the fuel
rail, and attach a fuel pressure gauge directly
to the hose. Note:If the tee fitting is still
connected to the gauge, be sure to plug the
open end.
22Reconnect the battery.
23Using a jumper wire, bridge the terminals
of the fuel pump relay.
24Turn the ignition switch on to operate the
fuel pump.
25Note the pressure reading on the gauge,
and compare the reading to the fuel pump
pressure listed in this Chapter’s Specifica-
tions.
26If the indicated pressure is less than
specified, inspect the fuel line for leaks
between the pump and gauge. If no leaks are
found, renew the fuel pump.
27Turn the ignition off and wait five minutes.
Note the reading on the gauge, and compare
it to the fuel pump hold pressure listed in this
Chapter’s Specifications. If the hold pressure
is less than specified, check the fuel lines
between the pump and gauge for leaks. If no
leaks are found, renew the fuel pump.
28Remove the jumper wire. Relieve the fuel
pressure by opening the bleed valve on the
gauge and directing the fuel into a suitable
container. Remove the gauge and reconnect
the fuel line.
Transfer pump pressure check
29Depressurise the fuel system (see Sec-
tion 2).
30Detach 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.
31Remove the transfer pump access plate
(on some models, it’s located under the rear
seat cushion - on others, it’s located under
the carpet in the luggage compartment).
Disconnect the output hose from the transfer
pump, and connect a fuel pressure gauge to
the outlet pipe.
32Reconnect the battery.33Using a jumper wire, bridge the terminals
of the fuel pump relay.
34Turn the ignition switch on to operate the
fuel pump.
35Note the pressure reading on the gauge,
and compare to the value listed in this
Chapter’s Specifications.
36If the indicated pressure is less than
specified, renew the transfer pump.
Fuel pump relay check
37Switch on the ignition.
38Using a voltmeter, probe the following
terminals from the back of the relay electrical
connector. Check for battery voltage at
terminal 30 (M20 and M30 engines) or
terminal 15 (M10 and M40 engines). Note:If
there is no voltage on models with luggage
compartment-mounted batteries, check for a
faulty fusible link. The 50-amp link is about
6 inches from the battery, in a black wire.
39Turn the ignition off, and disconnect the
relay from the electrical connector. Using a
voltmeter, probe the connector terminals that
correspond to fuel pump relay pins 85 (-) and
86(+) on M20 and M30 engines, or terminal 50
and earth on M10 and M40 engines. Have an
assistant turn the engine over on the starter,
and observe the voltage reading. Battery
voltage should be indicated.
40If there is no voltage, check the fuse(s)
and the wiring circuit for the fuel pump relay. If
the voltage readings are correct, and the fuel
pump only runs with the jumper wire in place,
then renew the relay.
41If the fuel pump still does not run, check
for the proper voltage at the fuel pump
terminals (see Section 4). If necessary, renew
the fuel pump.
4 Fuel pump, transfer pump
and fuel level sender unit-
removal and refitting
2
Warning: Fuel is extremely
flammable, so take extra
precautions when you work on
any part of the fuel system. Don’t
smoke, or allow open flames or bare light
bulbs, near the work area. Also, don’t work
in a garage where a natural gas-type
appliance with a pilot light is present.
Fuel pump (carburettor engines)
1Disconnect the battery negative cable.
Disconnect both hoses from the pump, and
unscrew and remove the two securing nuts
(see illustration).
2Carefully withdraw the pump from the
cylinder head. If it’s stuck, a slight downward
tap on the thick insulating distance piece with
a piece of wood, should free it.
3Remove the two thin gaskets.
4The fuel pump is a sealed unit, and it is not
possible to renew any of the internal
components. Should an internal fault occur, it
must be renewed complete.5Refitting is a reversal of the removal
procedure, but renew the thin gaskets each
side of the insulating distance piece, and
tighten the fuel pump down evenly to the
torque stated in the Specifications. On no
account alter the thickness of the distance
piece, or the correct operation of the fuel
pump will be upset.
Fuel pump (fuel injection
engines)
Note 1: The electric fuel pump is located
inside the fuel tank on later models with the
Motronic system, or adjacent to the fuel tank
on the L-Jetronic system. The early models
are also equipped with a transfer pump
located in the fuel tank. The transfer pump
feeds the larger main pump, which delivers
the high pressure required for proper fuel
system operation.
Note 2: The fuel level sender unit is located in
the fuel tank with the transfer pump on early
models, or with the main fuel pump on later
models.
6Depressurise the fuel system (see Sec-
tion 2) and remove the fuel tank filler cap to
relieve pressure in the tank.
7Disconnect 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.
Externally-mounted fuel pump
8Raise and support the vehicle.
9Remove the two rubber boots that protect
the fuel pump connectors, and disconnect the
wires from the pump (see illustration).
10Using hose clamps, pinch shut the fuel
hoses on each side of the fuel pump. If you
don’t have any hose clamps, wrap the hoses
with rags, and clamp them shut with self-
locking pliers, tightened just enough to
prevent fuel from flowing out.
11Disconnect the hoses from the pump.
12Remove the fuel pump mounting screws
Fuel and exhaust systems 4•5
4.1 Fuel pump on carburettor engines
4
Page 102 of 228
Throttle positioner (2BE)
24Special tools are required to carry out a
comprehensive adjustment on the 2BE
carburettor. This work should therefore be left
to a BMW dealer.
13 Fuel injection -
general information
The fuel injection system is composed of
three basic sub-systems: fuel system, air
intake system and electronic control system.
Fuel system
An electric fuel pump, located inside the
fuel tank or beside the fuel tank, supplies fuel
under constant pressure to the fuel rail, which
distributes fuel evenly to all injectors. From
the fuel rail, fuel is injected into the intake
ports, just above the intake valves, by the fuel
injectors. The amount of fuel supplied by the
injectors is precisely controlled by an
Electronic Control Unit (ECU). An additional
injector, known as the cold start injector (L-
Jetronic and early Motronic systems only),
supplies extra fuel into the intake manifold for
starting. A pressure regulator controls system
pressure in relation to intake manifold
vacuum. A fuel filter between the fuel pump
and the fuel rail filters the fuel, to protect the
components of the system.
Air intake system
The air intake system consists of an air filter
housing, an airflow meter, a throttle body, the
intake manifold, and the associated ducting.
The airflow meter is an information-gathering
device for the ECU. These models are
equipped with the vane-type airflow meter. A
potentiometer measures intake airflow, and a
temperature sensor measures intake air
temperature. This information helps the ECU
determine the amount of fuel to be injected by
the injectors (injection duration). The throttle
plate inside the throttle body is controlled by
the driver. As the throttle plate opens, the
amount of air that can pass through the
system increases, so the potentiometer opens
further and the ECU signals the injectors to
increase the amount of fuel delivered to the
intake ports.
Electronic control system
The computer control system controls the
fuel system and other systems by means of
an Electronic Control Unit (ECU). The ECU
receives signals from a number of information
sensors which monitor such variables as
intake air volume, intake air temperature,
coolant temperature, engine rpm,
acceleration/deceleration, and exhaust
oxygen content. These signals help the ECU
determine the injection duration necessary for
the optimum air/fuel ratio. These sensors and
their corresponding ECU-controlled outputactuators are located throughout the engine
compartment. For further information
regarding the ECU and its relationship to the
engine electrical systems and ignition system,
refer to Chapters 5 and 6.
Either an L-Jetronic system or a Motronic
system is fitted. Later models have an
updated version of the original Motronic
system.
14 Fuel injection systems
L-Jetronic fuel injection system
The Bosch L-Jetronic fuel injection system
is used on most 3-Series models up to 1987,
and on most E28 (“old-shape”) 5-Series
models. It is an electronically-controlled fuel
injection system that utilises one solenoid-
operated fuel injector per cylinder. The system
is governed by an Electronic Control Unit
(ECU) which processes information sent by
various sensors, and in turn precisely
meters the fuel to the cylinders by
adjusting the amount of time that the injectors
are open.
An electric fuel pump delivers fuel under
high pressure to the injectors, through the fuel
feed line and an in-line filter. A pressure
regulator keeps fuel available at an optimum
pressure, allowing pressure to rise or fall
depending on engine speed and load. Any
excess fuel is returned to the fuel tank by a
separate line.
A sensor in the air intake duct constantly
measures the mass of the incoming air, and
the ECU adjusts the fuel mixture to provide an
optimum air/fuel ratio.
Other components incorporated in the
system are the throttle valve (which controls
airflow to the engine), the coolant temperature
sensor, the throttle position switch, idle
stabiliser valve (which bypasses air around
the throttle plate to control idle speed) and
associated relays and fuses.
Motronic fuel injection system
The Motronic system combines the fuel
control of the L-Jetronic fuel injection system
with the control of ignition timing, idle speed
and emissions into one control unit.
The fuel injection and idle speed control
functions are similar to those used on the L-
Jetronic system described above. For more
information on the Motronic system, see
Chapter 6.
An oxygen sensor is mounted in the
exhaust system on later models with a
catalytic converter. This sensor continually
reads the oxygen content of the exhaust gas.
The information is used by the ECU to adjust
the duration of injection, making it possible to
adjust the fuel mixture for optimum converter
efficiency and minimum emissions.
15 Fuel injection system-
check
2
Warning: Fuel is extremely
flammable, so take extra
precautions when you work on
any part of the fuel system. Don’t
smoke, or allow open flames or bare light
bulbs, near the work area. Don’t work in a
garage where a natural gas-type appliance
(such as a water heater or clothes dryer)
with a pilot light is present. If you spill any
fuel on your skin, rinse it off immediately
with soap and water. When you perform
any kind of work on the fuel system, wear
safety glasses, and have a fire
extinguisher on hand.
1Check the earth wire connections. Check
all wiring harness connectors that are related
to the system. Loose connectors and poor
earths can cause many problems that
resemble more serious malfunctions.
2Make sure the battery is fully charged, as
the control unit and sensors depend on an
accurate supply voltage in order to properly
meter the fuel.
3Check the air filter element - a dirty or
partially-blocked filter will severely impede
performance and economy (see Chapter 1).
4If a blown fuse is found, renew it and see if
it blows again. If it does, search for an earthed
wire in the harness related to the system.
5Check the air intake duct from the airflow
meter to the intake manifold for leaks. Intake
air leaks can cause a variety of problems. Also
check the condition of the vacuum hoses
connected to the intake manifold.
6Remove the air intake duct from the throttle
body, and check for dirt, carbon and other
residue build-up. If it’s dirty, clean it with
carburettor cleaner and a toothbrush.
7With the engine running, place a
screwdriver or a stethoscope against each
injector, one at a time, and listen for a clicking
sound, indicating operation (see illustration).
4•14 Fuel and exhaust systems
15.7 Use a stethoscope or screwdriver to
determine if the injectors are working
properly - they should make a steady
clicking sound that rises and falls with
engine speed changes
Page 103 of 228
8Check the fuel system pressure (see
Section 3).
9If these checks do not locate the problem,
take the vehicle to a BMW dealer, who will be
able to read the fault codes stored in the ECU,
using special equipment.
16 Airflow meter- check,
removal and refitting
2
Check (L-Jetronic systems)
1Remove the duct from the intake end of the
airflow meter. Carefully open and close the
sensor flap (see illustration), and check for
binding. The flap can bend during a backfire,
and cause incorrect resistance readings. The
flap will bind and stick in a partially-open
position, causing the engine to run rich, and
stall when it returns to idle.
2Disconnect the electrical connector from
the airflow meter.
3Using an ohmmeter, check the resistancebetween terminals 7 and 8 (see illustration).
The resistance should increase steadily
(without any “flat spots”) as the sensor flap is
slowly moved from the fully-closed position to
the fully-open position.
4Also, check the intake air temperature
sensor (inside the airflow meter). Using an
ohmmeter, probe terminals 8 and 9 (see
illustration 16.3)and check for the proper
resistance. The resistance should be 2200 to
2700 ohms at 20º C.
5If the resistance readings are correct, check
the wiring harness (see Chapter 12). Plug in
the connector to the airflow meter. Ensure
that the ignition is switched off. Disconnect
the electrical connector from the ECU (located
under the right-hand side of the facia) and
probe terminals 7 and 8 (see illustration)with
an ohmmeter. Carefully move the door of the
airflow meter, and observe the change in
resistance as it moves from closed to fully-
open. The test results should be the same as
paragraph 3. If there are any differences in the
test results, there may be a shorted-out or
broken wire in the harness.
Check (Motronic systems)
6Ensure that the ignition is switched off.Remove the ECU access cover (see Chap-
ter 6) and disconnect the harness connector
(see illustration).
7Using an ohmmeter, probe the designated
terminals of the ECU electrical connector (see
illustrations)and check for the proper
change in resistance while moving the sensor
flap. On early Motronic systems, probe
terminals 7 and 9. On later Motronic systems,
probe terminals 7 and 12. The resistance
should increase steadily (without any “flat
spots”) as the sensor flap is slowly moved
from the fully-closed position to the fully-open
position. Note: Early Motronic systems are
distinguishable by the 35-pin ECU electrical
connector; later Motronic systems use a 55-
pin connector.
8If the resistance readings are incorrect,
check the wiring harness.
Removal and refitting (all
systems)
9Disconnect the electrical connector from
the airflow meter.
10Remove the air cleaner assembly (see
Section 8).
11Remove the nuts (see illustrations), and
lift the airflow meter from the engine
compartment or from the air cleaner
assembly.
12Refitting is the reverse of removal.
Fuel and exhaust systems 4•15
16.5 The ECU is located under the right-
hand side of the facia. Unplug the
electrical connector, and check the
resistance between terminals 7 and 8 as in
paragraph 3. The test results should be the
same.
16.3 Connect an ohmmeter to terminals 7
and 8 of the airflow meter, and check for a
smooth change in resistance as the vane
door of the airflow meter is slowly opened
and closed16.1 Check for binding of the flap in the
airflow meter as it nears closing position
or wide-open position. Any hesitation or
binding will cause erratic idle conditions,
rich fuel mixture or poor acceleration and
throttle response (airflow meter removed
for clarity)
16.7b Unplug the connector, connect the
ohmmeter probes to terminals 7 and 9
(early Motronic systems) and check for a
smooth change in resistance as the door
on the airflow meter is slowly opened and
closed16.7a Connect the ohmmeter probes to
terminals 7 and 12 (later Motronic systems)
of the ECU connector and check for a
smooth change in resistance as the door
on the airflow meter is slowly opened and
closed16.6 Remove the under-facia panel to gain
access to the ECU on Motronic systems
(left-hand-drive model shown)
4