1986 BMW 3 SERIES not starting

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

terminals and cable clamps after they are
assembled.
9Make sure that the battery carrier is in good
condition, and that the hold-down clamp bolt
is tight. If the battery is removed (see Chap-
ter 5 for the removal and refitting procedure),
make sure that no parts remain in the bottom
of the carrier when it’s refitted. When refitting
the hold-down clamp, don’t overtighten the
bolt.
10Corrosion on the carrier, battery case and
surrounding areas can be removed with a
solution of water and baking soda. Apply the
mixture with a small brush, let it work, then
rinse it off with plenty of clean water.
11Any metal parts of the vehicle damaged
by corrosion should be coated with a zinc-
based primer, then painted.
12Additional information on the battery and
jump starting can be found in Chapter 5 and
the front of this manual.
Charging
Note: The manufacturer recommends the
battery be removed from the vehicle for
charging, because the gas which escapes
during this procedure can damage the paint or
interior, depending on the location of the
battery. Fast charging with the battery cables
connected can result in damage to the
electrical system.
13Remove all of the cell caps (if applicable),
and cover the holes with a clean cloth to
prevent spattering electrolyte. Disconnect thebattery negative cable, and connect the
battery charger leads to the battery posts
(positive to positive, negative to negative),
then plug in the charger. Make sure it is set at
12 volts if it has a selector switch.
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.
14If you’re using a charger with a rate higher
than two amps, check the battery regularly
during charging to make sure it doesn’t
overheat. If you’re using a trickle charger, you
can safely let the battery charge overnight
after you’ve checked it regularly for the first
couple of hours. Where a maintenance-free
battery is fitted, special precautions may be
necessary when charging it (for example, the
charge rate is normally very low). There may
be a warning label on the battery, but if not,
consult a BMW dealer or auto-electrician.
15If the battery has removable cell caps,
measure the specific gravity with a
hydrometer every hour during the last few
hours of the charging cycle. Hydrometers are
available inexpensively from car accessory
shops - follow the instructions that come with
the hydrometer. Consider the battery charged
when there’s no change in the specific gravity
reading for two hours, and the electrolyte in
the cells is gassing (bubbling) freely. The
specific gravity reading from each cell should
be very close to the others. If not, the battery
probably has a bad cell(s), and a new one
should be fitted.
16Some maintenance-free (sealed) batteries
have built-in hydrometers on the top,
indicating the state of charge by the colour
displayed in the hydrometer window.
Normally, a bright-coloured hydrometer
indicates a full charge, and a dark hydrometer
indicates the battery still needs charging.
Check the battery manufacturer’s instructions
to be sure you know what the colours mean.17If the battery is sealed and has no built-in
hydrometer, you can connect a digital
voltmeter across the battery terminals to
check the charge. A fully-charged battery
should read 12.6 volts or higher.
18Further information on the battery and
jump starting can be found in Chapter 5 and
at the front of this manual.
14 Spark plug check and
renewal
1
1Before beginning, obtain the necessary
tools, which will include a spark plug socket
and a set of feeler blades. Special spark plug
gap gauges can be obtained from certain
spark plug manufacturers (see illustration).
2The best procedure to follow when
renewing the spark plugs is to purchase the
new spark plugs beforehand, adjust them to
the proper gap, and then renew each plug one
at a time. When buying the new spark plugs, it
is important to obtain the correct plugs for
your specific engine. This information can be
found in the Specifications section in the front
of this Chapter.
3With the new spark plugs at hand, allow the
engine to cool completely before attempting
plug removal. During this time, each of the
new spark plugs can be inspected for defects
and the gaps can be checked.
4The gap is checked by inserting the proper
thickness gauge between the electrodes at the
tip of the plug (see illustration). The gap
between the electrodes should be the same as
that given in the Specifications. The wire
should just touch each of the electrodes. If the
gap is incorrect, use the notched adjuster to
bend the curved side of the electrode slightly
until the proper gap is achieved (see
illustration). Note: When adjusting the gap of a
new plug, bend only the base of the earth
electrode, do not touch the tip. If the earth
electrode is not exactly over the centre
electrode, use the notched adjuster to align the
two. Check for cracks in the porcelain insulator,
indicating the spark plug should not be used.
1•17
14.4b To change the gap, bend the earth
electrode only, as indicated by the arrows,
and be very careful not to crack or chip the
porcelain insulator surrounding the centre
electrode14.4a Spark plug manufacturers
recommend using a wire-type gauge when
checking the gap - if the wire does not
slide between the electrodes with a slight
drag, adjustment is required
14.1 Tools required for changing spark
plugs
1 Spark plug socket- This will have special
padding inside to protect the spark plug’s
porcelain insulator
2 Torque wrench - Although not mandatory,
using this tool is the best way to ensure the
plugs are tightened properly
3 Ratchet - Standard hand tool to fit the
spark plug socket
4 Extension - Depending on model and
accessories, you may need special
extensions and universal joints to reach one
or more of the plugs
5 Spark plug gap gauge- This gauge for
checking the gap comes in a variety of
styles. Make sure the gap for your engine is
included. Feeler blades may be used
instead
1
Every 12 000 miles

6 Exhaust manifold-
removal and refitting
1
Warning: Make sure the engine is
completely cool before beginning
work on the exhaust system.
Caution: If the radio in your
vehicle is equipped with an anti-
theft system, make sure you
have the correct activation code
before disconnecting the battery.
Note: If, after connecting the battery, the
wrong language appears on the instrument
panel display, refer to page 0-7 for the
language resetting procedure.
1Disconnect the battery negative cable.
2On models where the air cleaner is on the
exhaust manifold side of the engine, remove
the air cleaner housing assembly and/or
airflow sensor to provide sufficient working
area (see Chapter 4, if necessary).
3Unplug the HT leads and set the spark plug
lead harness aside (see Chapter 1).
4Clearly label, then disconnect or remove, all
wires, hoses, fittings, etc. that are in the way.
Be sure to disconnect the oxygen sensor,
where fitted.
5Raise the vehicle, and support it securely
on axle stands. Working from under the
vehicle, separate the exhaust downpipe from
the manifold. Use penetrating oil on the
fasteners to ease removal (see illustrations).
6Remove the axle stands, and lower the
vehicle. Working from the ends of the
manifold toward the centre, loosen the
retaining nuts gradually until they can be
removed. Again, penetrating oil may prove
helpful.
7Pull the manifold off the head, then remove
the old gaskets (see illustrations). Note:Be
very careful not to damage the oxygen sensor,
where fitted.8Clean the gasket mating surfaces of the
head and manifold, and make sure the
threads on the exhaust manifold studs are in
good condition.
9Check for corrosion, warping, cracks, and
other damage. Repair or renew the manifold
as necessary.
10When refitting the manifold, use new
gaskets. Tighten the manifold-to-head
retaining nuts gradually, starting at the centre
and working out to the ends, to the torque
listed in this Chapter’s Specifications. Also
tighten the downpipe-to-manifold nuts.
11The remaining steps are simply a reversal
of the removal procedure.
7 Timing chain covers-
removal and refitting
5
Note 1:This procedure applies to M10 and
M30 engines.
Note 2:The upper timing chain cover can be
removed separately. If you need to remove
both the upper and lower covers, special tools
are required. Read paragraphs 8 and 9 before
beginning work.
Removal
1Disconnect the battery negative cable.Caution: If the radio in your
vehicle is equipped with an anti-
theft system, make sure you
have the correct activation code before
disconnecting the battery.
Note: If, after connecting the battery, the
wrong language appears on the instrument
panel display, refer to page 0-7 for the
language resetting procedure.
2If you’re removing the lower timing chain
cover (the upper cover can be removed
separately), remove the cooling fan and fan
shroud, the radiator and the fan drivebelt
pulley (see Chapter 3).
3On the M10 engine only, remove the water
pump (see Chapter 3).
4On engines where the distributor cap is
mounted directly to the timing chain cover,
remove the cap, rotor and the black plastic
cover beneath the rotor (see Chapter 1).
5On the M30 engine fitted with the
L-Jetronic fuel system, remove the
distributor from the upper timing cover (see
Chapter 5).
6Remove the valve cover (see Section 4).
7If you’ll be removing the lower timing chain
cover on the M30 engine, remove the crankshaft
pulley from the vibration damper/hub. Hold the
pulley stationary with a socket on the centre
bolt, and remove the pulley bolts with another
socket (see illustration).
8If you’ll be removing the lower timing chain
2A•6 In-car engine repair procedures
6.7c Removing the exhaust manifold-to-
downpipe gasket (M40 engine)6.7b Removing the exhaust manifold
gasket (M40 engine)6.7a Removing the exhaust manifold
(M40 engine)
6.5b Exhaust manifold-to-downpipe flange
(M40 engine)6.5a Remove the exhaust manifold nuts
(arrowed) from the exhaust pipe (M20
engine) - soaking the nuts with penetrating
oil should make them easier to remove
Remove the windscreen
washer reservoir from the
right-hand side of the engine
compartment to give more
working room.

6If coarse grinding compound is being used,
work only until a dull, matt even surface is
produced on both the valve seat and the
valve, then wipe off the used compound and
repeat the process with fine compound. When
a smooth, unbroken ring of light grey matt
finish is produced on both the valve and seat,
the grinding operation is complete. Do not
grind in the valves any further than absolutely
necessary.
7When all the valves have been ground-in,
carefully wash off all traces of grinding
compound using paraffin or a suitable solvent
before reassembly of the cylinder head.
11 Cylinder head- reassembly
5
1Make sure the cylinder head is spotlessly-
clean before beginning reassembly.
2If the head was sent out for valve servicing,
the valves and related components will
already be in place. Begin the reassembly
procedure with paragraph 8.
3Starting at one end of the head, applymolybdenum disulphide (“moly”) grease or
clean engine oil to each valve stem, and refit
the first valve.
4Lubricate the lip of the valve guide seal,
carefully slide it over the tip of the valve, then
slide it all the way down the stem to the guide.
Using a hammer and a deep socket or seal-
fitting tool, gently tap the seal into place until
it’s completely seated on the guide (see
illustrations). Don’t twist or distort a seal
during fitting, or it won’t seal properly against
the valve stem. Note:On some engines, the
seals for intake and exhaust valves are
different - don’t mix them up.
5Drop the spring seat or shim(s) over the
valve guide, and set the valve spring and
retainer in place.
6Compress the spring with a valve spring
compressor and carefully refit the collets in
the upper groove, then slowly release the
compressor and make sure the collets seat
properly (see illustration).
7Repeat paragraphs 3 to 6 for each of the
valves. Be sure to return the components to
their original locations - don’t mix them up!
M10, M20 and M30 engines
8Refit the rocker arms and shafts by
reversing the dismantling sequence. Be sure
to refit the rocker shafts in the correct
orientation. The guide plate notches and the
small oil holes face inwards; the large oil holes
face down, toward the valve guides.
9Lubricate the camshaft journals and lobes(see illustration), then carefully insert it into
the cylinder head, rotating it as you go so the
camshaft lobes will clear the rocker arms. It
will also be necessary to compress the rocker
arms against the valve springs, as described
in Section 8, so they’ll clear the camshaft
lobes. Be very careful not to scratch or gouge
the camshaft bearing surfaces in the cylinder
head.
M40 engines
10Lubricate the bores for the hydraulic
tappets in the cylinder head, then insert the
tappets in their original positions.
11Locate the thrust discs and cam followers
on the valves and pivot posts in their original
positions.
12Lubricate the bearing surfaces of the
camshaft in the cylinder head.
13Locate the camshaft in the cylinder head
so that the valves of No 1 cylinder are both
open, and the valves of No 4 cylinder are
“rocking” (exhaust closing and inlet opening).
No 1 cylinder is at the timing belt end.
14Lubricate the bearing surfaces in the
bearing caps, then locate them in their correct
positions and insert the retaining bolts.
Progressively tighten the bolts to the specified
torque.
15Fit a new oil seal to the camshaft front
bearing cap (see Chapter 2A, Section 11).
All engines
16Refit the oil supply tube to the top of the
cylinder head together with new seals, then
tighten the bolts to the specified torque.
17The cylinder head may now be refitted
(see Chapter 2A).
12 Pistons/connecting rods-
removal
5
Note:Before removing the piston/connecting
rod assemblies, remove the cylinder head and
the sump. On M10, M20 and M30 engines
only, remove the oil pump. Refer to the
appropriate Sections in Chapter 2A.
1Use your fingernail to feel if a ridge has
formed at the upper limit of ring travel (about
6 mm down from the top of each cylinder). If
2B•12 General engine overhaul procedures
11.9 Lubricate the camshaft bearing
journals and lobes with engine assembly
paste or molybdenum disulphide (“moly”)
grease
11.6 With the retainer fitted, compress the
valve spring and refit the collets as shown 11.4b . . .then lightly drive on the seal with
a socket or piece of tubing11.4a Lubricate the valve guide seal, and
place it on the guide (the valve should be
in place too) . . .
A light spring placed under
the valve head will greatly
ease the valve grinding
operation.
Apply a small dab of grease to each
collet to hold it in place, if necessary.

positions (don’t mix them up) with the arrows
pointing towards the front of the engine. Don’t
disturb the Plastigage.
13Starting with the centre main bearing and
working out toward the ends, progressively
tighten the main bearing cap bolts to the
torque listed in this Chapter’s Specifications.
On M10, M20 and M30 engines, tighten the
bolts in three stages. On the M40 engine,
tighten all the bolts initially to the Stage 1
torque, then angle-tighten them by the angle
given in the Specifications. Carry out the
angle-tightening on each bolt in one
controlled movement. Don’t rotate the
crankshaft at any time during the tightening
operation.
14Remove the bolts and carefully lift off the
main bearing caps. Keep them in order. Don’t
disturb the Plastigage or rotate the
crankshaft. If any of the main bearing caps are
difficult to remove, tap them gently from side-
to-side with a soft-face hammer to loosen
them.
15Compare the width of the crushed
Plastigage on each journal to the scale printed
on the Plastigage envelope to obtain the main
bearing oil clearance (see illustration). Check
the Specifications to make sure it’s correct.
16If the clearance is not as specified, thebearing shells may be the wrong size (which
means different ones will be required). Before
deciding that different shells are needed,
make sure that no dirt or oil was between the
bearing shells and the caps or block when the
clearance was measured. If the Plastigage
was wider at one end than the other, the
journal may be tapered (see Section 19).
17Carefully scrape all traces of the
Plastigage material off the main bearing
journals and/or the bearing faces. Use your
fingernail or the edge of a credit card - don’t
nick or scratch the bearing faces.
Final crankshaft refitting
18Carefully lift the crankshaft out of the
engine.
19Clean the bearing faces in the block, then
apply a thin, uniform layer of molybdenum
disulphide (“moly”) grease or engine oil to
each of the bearing surfaces. Be sure to coat
the thrust faces as well as the journal face of
the thrust bearing.
20Make sure the crankshaft journals are
clean, then lay the crankshaft back in place in
the block.
21Clean the faces of the bearings in the
caps, then apply engine oil to them.
22Refit the caps in their respective
positions, with the arrows pointing towards
the front of the engine.
23Refit the bolts finger-tight.
24Lightly tap the ends of the crankshaft
forward and backward with a lead or brass
hammer, to line up the main bearing and
crankshaft thrust surfaces.
25Tighten the bearing cap bolts to the
specified torque, working from the centre
outwards. On M10, M20 and M30 engines,
tighten the bolts in three stages to the final
torque, leaving out the thrust bearing cap
bolts at this stage. On M40 engines, tighten all
of the bolts in the two stages given in the
Specifications.
26On M10, M20 and M30 engines, tighten
the thrust bearing cap bolts to the torque
listed in this Chapter’s Specifications.
27On manual transmission models, fit a new
pilot bearing in the end of the crankshaft (see
Chapter 8).28Rotate the crankshaft a number of times
by hand to check for any obvious binding.
29The final step is to check the crankshaft
endfloat with a feeler gauge or a dial indicator
as described in Section 13. The endfloat
should be correct, providing the crankshaft
thrust faces aren’t worn or damaged, and new
bearings have been fitted.
30Fit the new seal, then bolt the housing to
the block (see Section 25).
25 Crankshaft rear oil seal-
refitting
3
1The crankshaft must be fitted first, and the
main bearing caps bolted in place. The new
seal should then be fitted in the retainer, and
the retainer bolted to the block.
2Before refitting the crankshaft, check the
seal contact surface very carefully for
scratches and nicks that could damage the
new seal lip and cause oil leaks. If the
crankshaft is damaged, the only alternative is
a new or different crankshaft, unless a
machine shop can suggest a means of repair.
3The old seal can be removed from the
housing with a hammer and punch by driving
it out from the back side (see illustration). Be
sure to note how far it’s recessed into the
housing bore before removing it; the new seal
will have to be recessed an equal amount. Be
very careful not to scratch or otherwise
damage the bore in the housing, or oil leaks
could develop.
4Make sure the retainer is clean, then apply
a thin coat of engine oil to the outer edge of
the new seal. The seal must be pressed
squarely into the housing bore, so hammering
it into place is not recommended. At the very
least, use a block of wood as shown, or a
section of large-diameter pipe (see
illustration). If you don’t have access to a
press, sandwich the housing and seal
between two smooth pieces of wood, and
press the seal into place with the jaws of a
large vice. The pieces of wood must be thick
enough to distribute the force evenly around
the entire circumference of the seal. Work
2B•20 General engine overhaul procedures
25.5 Lubricate the lip of the seal, and bolt
the retainer to the rear of the engine block25.4 Drive the new seal into the retainer
with a wooden block or a section of pipe, if
you have one large enough - make sure
the seal enters the retainer bore squarely25.3 After removing the retainer from the
block, support it on two wooden blocks,
and drive out the old seal with a punch and
hammer
24.15 Compare the width of the crushed
Plastigage to the scale on the envelope to
determine the main bearing oil clearance
(always take the measurement at the
widest point of the Plastigage); be sure to
use the correct scale - standard and
metric ones are included

the bearing - use your fingernail or the edge of
a credit card.
20Make sure the bearing faces are perfectly
clean, then apply a uniform layer of
molybdenum disulphide (“moly”) grease or
engine assembly oil to both of them. You’ll
have to push the piston into the cylinder to
expose the face of the bearing shell in the
connecting rod - be sure to slip the protective
hoses over the rod bolts first, where
applicable.
21Slide the connecting rod back into place
on the journal, and remove the protective
hoses from the rod cap bolts. Refit the rod
cap, and tighten the nuts/bolts to the
specified torque.
22Repeat the entire procedure for the
remaining pistons/connecting rods.
23The important points to remember are:
a) Keep the back sides of the bearing shells
and the insides of the connecting rods
and caps perfectly clean when
assembling them.
b) Make sure you have the correct
piston/rod assembly for each cylinder.
c) The notch or mark on the piston must
face the front of the engine.
d) Lubricate the cylinder walls with clean oil.
e) Lubricate the bearing faces when refitting
the rod caps after the oil clearance has
been checked.
24After all the piston/connecting rod
assemblies have been properly fitted, rotate
the crankshaft a number of times by hand to
check for any obvious binding.25Check the connecting rod side play (see
Section 13).
26Compare the measured side play to the
Specifications to make sure it’s correct. If it
was correct before dismantling, and the
original crankshaft and rods were refitted, it
should still be right. If new rods or a new
crankshaft were fitted, the side play may be
incorrect. If so, the rods will have to be
removed and taken to a machine shop for
attention.
27 Initial start-up and running-
in after overhaul
1
Warning:Have a fire extinguisher
handy when starting the engine
for the first time.
1Once the engine has been refitted in the
vehicle, double-check the engine oil and
coolant levels.
2With the spark plugs removed and the
ignition system disabled (see Section 3), crank
the engine until oil pressure registers on the
gauge, or until the oil pressure warning light
goes out.
3Refit the spark plugs, connect the HT leads,
and restore the ignition system functions (see
Section 3).
4Start the engine. It may take a few
moments for the fuel system to build uppressure, but the engine should start without
a great deal of effort. Note: If backfiring
occurs through the throttle body or
carburettor, check the valve timing (check that
the timing chain/belt has been correctly fitted),
the firing order (check the fitted order of the
spark plug HT leads), and the ignition timing.
5After the engine starts, it should be allowed
to warm up to normal operating temperature.
While the engine is warming up, make a
thorough check for fuel, oil and coolant leaks.
6Shut the engine off and recheck the engine
oil and coolant levels.
7Drive the vehicle to an area with minimum
traffic, accelerate at full throttle from 30 to
50 mph, then lift off the throttle completely,
and allow the vehicle to slow to 30 mph with
the throttle closed. Repeat the procedure
10 or 12 times. This will load the piston rings,
and cause them to seat properly against the
cylinder walls. Check again for oil and coolant
leaks.
8Drive the vehicle gently for the first
500 miles (no sustained high speeds) and
keep a constant check on the oil level. It is not
unusual for an engine to use oil during the
running-in period.
9At approximately 500 to 600 miles, change
the oil and filter.
10For the next few hundred miles, drive the
vehicle normally - don’t nurse it, but don’t
abuse it, either.
11After 2000 miles, change the oil and filter
again. The engine may now be considered to
be fully run-in.
2B•22 General engine overhaul procedures

6If the voltage is correct, unplug the
electrical connector and, using an ohmmeter,
check for continuity between the terminals of
the thermotime switch (see illustration).
Continuity should exist.
7Reconnect the coil lead, start the engine
and warm it up above 41ºC. When the engine
is warm, there should be no continuity
between the terminals. If there is, the switch is
faulty and must be renewed. Note: On 5-
Series models, there are several types of
thermotime switch. Each one is stamped with
an opening temperature and maximum
duration.
Renewal
Cold start injector
8Depressurise the fuel system (see Sec-
tion 2).
9Disconnect the electrical connector from
the cold start injector.
10Where applicable, using a ring spanner or
deep socket, remove the fuel line fitting
connected to the cold start injector. On other
models, simply loosen the hose clamp and
detach the hose from the injector.
11Remove the cold start injector securing
bolts, and remove the injector.
12Refitting is the reverse of removal. Clean
the mating surfaces, and use a new gasket.
Thermotime switch
Warning: Wait until the engine is
completely cool before beginning
this procedure. Also, remove the
cap from the expansion tank or
radiator to relieve any residual pressure in
the cooling system.
13Prepare the new thermotime switch for
fitting by applying a light coat of thread
sealant to the threads.
14Disconnect the electrical connector from
the old thermotime switch.
15Using a deep socket, or a ring spanner,
unscrew the switch. Once the switch is
removed coolant will start to leak out, so
insert the new switch as quickly as possible.
Tighten the switch securely, and plug in the
electrical connector.
20 Fuel injectors-
check and renewal
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.
Check
In-vehicle check
1Using a mechanic’s stethoscope (available
at most car accessory shops), check for a
clicking sound at each of the injectors while
the engine is idling (see illustration 15.7).
2The injectors should make a steady clicking
sound if they are operating properly.
3Increase the engine speed above 3500 rpm.
The frequency of the clicking sound should
rise with engine speed.
4If an injector isn’t functioning (not clicking),
purchase a special injector test light (a car
accessory shop or fuel injection specialist
may be able to help) and connect it to the
injector electrical connector. Start the engine
and make sure the light flashes. If it does, the
injector is receiving the proper voltage, so the
injector itself must be faulty.
5Unplug each injector connector, and checkthe resistance of the injector (see
illustration). Check your readings with the
values listed in this Chapter’s Specifications.
Renew any that do not give the correct
resistance reading.
Volume test
6Because a special injection checker is
required to test injector volume, this
procedure is beyond the scope of the home
mechanic. Have the injector volume test
performed by a BMW dealer or other
specialist.
Renewal
7Unplug the main electrical connector for the
fuel injector wiring harness. Remove the
intake manifold (see Chapter 2A).
8Detach the fuel hoses from the fuel rail, and
remove the fuel rail mounting bolts (see
illustration).
9Lift the fuel rail/injector assembly from the
intake manifold.
10Unplug the electrical connectors from the
fuel injectors. Detach the injectors from the
fuel rail.
11Refitting is the reverse of removal. Be sure
to renew all O-rings. Coat the O-rings with a
light film of engine oil to prevent damage
during refitting. Pressurise the fuel system
(refit the fuel pump fuse and switch on the
ignition) and check for leaks before starting
the engine.
21 Idle air stabiliser valve-
check, adjustment and
renewal
4
1The idle air stabiliser system works to
maintain engine idle speed within a 200 rpm
range, regardless of varying engine loads at
idle. An electrically-operated valve allows a
small amount of air to bypass the throttle
plate, to raise the idle speed whenever the idle
speed drops below approximately 750 rpm. If
the idle speed rises above approximately
950 rpm, the idle air stabiliser valve closes
and stops extra air from bypassing the throttle
plate, reducing the idle speed.
4•18 Fuel and exhaust systems
20.8 Remove the bolts (arrowed) and
separate the fuel rail and injectors from
the intake manifold20.5 Check the resistance of each of the
fuel injectors19.6 Check the resistance of the
thermotime switch with the engine coolant
temperature below 30º C. There should be
continuity
If you don’t have a
mechanic’s stethoscope, a
screwdriver can be used to
check for a clicking sound at
the injectors. Place the tip of the
screwdriver against the injector, and
press your ear against the handle.

1 General information
The engine electrical systems include all
ignition, charging and starting components.
Because of their engine-related functions,
these components are discussed separately
from body-related electrical devices such as
the lights, the instruments, etc. (which are
included in Chapter 12).
Always observe the following precautions
when working on the electrical systems:
a) Be extremely careful when servicing
engine electrical components. They are
easily damaged if improperly checked,
connected or handled.
b) Never leave the ignition switched on for
long periods of time with the engine off.
c) Don’t disconnect the battery cables while
the engine is running.
d) Observe the rules when jump-starting
your vehicle. Read the precautions at the
front of this manual.
e) Always disconnect the battery negative
cable first, and connect it last, to reduce
the risk of accidental short-circuits.
f) Don’t charge the battery with the cables
connected to the terminals.
It’s also a good idea to review the safety-
related information regarding the engine
electrical systems in the “Safety first”section
near the front of this manual before beginning
any operation included in this Chapter.
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.
2 Battery-
emergency jump starting
1
Refer to the “Jump starting”procedure at
the front of this manual.
3 Battery- removal and refitting
1
Note:Depending on the model, the battery
may be located in the engine compartment, in
the rear luggage compartment, or under the
rear seat. Consult your owners handbook for
the location of the battery, if not already
known to you.Caution: If the radio in your
vehicle is equipped with an anti-
theft system, make sure you
have the correct activation code
before disconnecting the battery. Refer to
the information on page 0-7 at the front of
this manual before detaching the cable.
Note: If, after connecting the battery, the
wrong language appears on the instrument
panel display, refer to page 0-7 for the
language resetting procedure.
1Disconnect the battery negative cable.
2Detach the cable from the positive terminal.
3Remove the battery hold-down bracket
(see illustrations)and lift out the battery. Be
careful - it’s heavy. Do not tilt the battery to
any extent while it is being removed, and
store it upright.
4While the battery is out, inspect the carrier
(tray) for corrosion (see Chapter 1).
5If you are renewing the battery, make sure
that you get one that’s identical, with the
same dimensions, amperage rating, cold
cranking rating, etc.
6Refitting is the reverse of removal.
4 Battery cables-
check and renewal
1
Check
1Periodically inspect the entire length of
each battery cable for damage, cracked or
burned insulation, and corrosion.
Poor battery cable connections can cause
starting problems and decreased engine
performance.
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.2Check the cable-to-terminal connections at
the ends of the cables for cracks, loose wire
strands, and corrosion. The presence of
white, fluffy deposits under the insulation at
the cable terminal connection is a sign that
the cable is corroded, and should be cleaned
or renewed. Check the terminals for
distortion, missing mounting bolts, and
corrosion.
Renewal
3When removing the cables, always
disconnect the negative cable first and
connect it up last. This reduces the risk of
accidental short-circuits. Even if only a new
positive cable is being fitted, be sure to
disconnect the negative cable from the
battery first (see Chapter 1 for further
information regarding battery cable removal).
4Disconnect the old cables from the battery,
then trace each of them to their opposite ends
and detach them from the starter solenoid
and earth terminals. Note the routing of each
cable to ensure correct refitting.
5If the old cables are to be renewed, take
them with you when buying new cables. It is
vitally important that you renew the cables
with identical parts. Cables have character-
istics that make them easy to identify: positive
cables are usually red, larger in cross-section,
and have a larger-diameter battery post
clamp; earth cables are usually black, smaller
in cross-section, and have a slightly smaller
diameter clamp for the negative post.
6Clean the threads of the solenoid or earth
connection with a wire brush to remove rust
and corrosion.
7Attach the cable to the solenoid or earth
connection, and tighten the mounting nut/bolt
securely.
8Before connecting a new cable to the
battery, make sure that it reaches the battery
post without having to be stretched.
9Connect the positive cable first, followed by
the negative cable.
5•2 Engine electrical systems
3.3b The battery is mounted under the
rear seat on some models
3.3a Always detach the cable from the
battery negative terminal first, then detach
the positive cable – to remove the hold-
down assembly, remove the nuts (arrowed)
or single bolt
Apply a light coat of battery
terminal corrosion inhibitor,
or petroleum jelly, to the
terminal threads, to prevent
future corrosion.