1986 BMW 3 SERIES Fuel

36Run the engine and check for leaks and
proper operation of all accessories, then refit
the bonnet and test drive the vehicle.
37Where necessary, have the air
conditioning system recharged and leak-
tested.
6 Engine overhaul- alternatives
The do-it-yourselfer is faced with a number
of options when performing an engine
overhaul. The decision to renew the engine
block, piston/connecting rod assemblies and
crankshaft depends on a number of factors,
with the number one consideration being the
condition of the block. Other considerations
are cost, access to machine shop facilities,
parts availability, time required to complete
the project, and the extent of prior mechanical
experience on the part of the do-it-yourselfer.
Some of the alternatives include:
Individual parts - If the inspection
procedures reveal that the engine block and
most engine components are in re-usable
condition, purchasing individual parts may be
the most economical alternative. The block,
crankshaft and piston/connecting rod
assemblies should all be inspected carefully.
Even if the block shows little wear, the
cylinder bores should be surface-honed.
Crankshaft kit- A crankshaft kit (where
available) consists of a reground crankshaft
with matched undersize new main and
connecting big-end bearings. Sometimes,
reconditioned connecting rods and new
pistons and rings are included with the kit
(such a kit is sometimes called an “engine
kit”). If the block is in good condition, but the
crankshaft journals are scored or worn, a
crankshaft kit and other individual parts may
be the most economical alternative.
Short block- A short block consists of an
engine block with a crankshaft and
piston/connecting rod assemblies already
fitted. New bearings are fitted, and all
clearances will be correct. The existing
camshaft, valve train components, cylinder
head and external parts can be bolted to the
short block with little or no machine shop
work necessary.
Full block - A “full” or “complete” block
consists of a short block plus an oil pump,
sump, cylinder head, valve cover, camshaft
and valve train components, timing sprockets
and chain (or belt) and timing cover. All
components are fitted with new bearings,
seals and gaskets used throughout. The
refitting of manifolds and external parts is all
that’s necessary.
Give careful thought to which alternative is
best for you, and discuss the situation with
local machine shops, parts dealers and
experienced rebuilders before ordering or
purchasing new parts.
7 Engine overhaul-
dismantling sequence
1It’s much easier to dismantle and work on
the engine if it’s mounted on a portable
engine stand. A stand can often be hired quite
cheaply from a tool hire shop. Before the
engine is mounted on a stand, the
flywheel/driveplate should be removed from
the engine.
2If a stand isn’t available, it’s possible to
dismantle the engine with it blocked up on the
floor. Be extra-careful not to tip or drop the
engine when working without a stand.
3If you’re going to obtain a rebuilt engine, all
the external components listed below must
come off first, to be transferred to the new
engine if applicable. This is also the case if
you’re doing a complete engine overhaul
yourself. Note:When removing the external
components from the engine, pay close
attention to details that may be helpful or
important during refitting. Note the fitted
position of gaskets, seals, spacers, pins,
brackets, washers, bolts and other small items.
Alternator and brackets
Emissions control components
Distributor, HT leads and spark plugs
Thermostat and housing cover
Water pump
Fuel injection/carburettor and fuel system
components
Intake and exhaust manifolds
Oil filter and oil pressure sending unit
Engine mounting brackets (see illustration)
Clutch and flywheel/driveplate
Engine rear plate (where applicable)
4If you’re obtaining a short block, which
consists of the engine block, crankshaft,
pistons and connecting rods all assembled,
then the cylinder head, sump and oil pump
will have to be removed as well. See Section 6
for additional information regarding the
different possibilities to be considered.
5If you’re planning a complete overhaul, the
engine must be dismantled and the internal
components removed in the following general
order:
Valve cover
Intake and exhaust manifolds
Timing belt or chain covers
Timing chain/belt
Water pump
Cylinder head
Sump
Oil pump
Piston/connecting rod assemblies
Crankshaft and main bearings
Camshaft
Rocker shafts and rocker arms (M10, M20
and M30 engines)
Cam followers and hydraulic tappets
(M40 engine)
Valve spring retainers and springs
Valves
6Before beginning the dismantling andoverhaul procedures, make sure the following
items are available. Also, refer to Section 21
for a list of tools and materials needed for
engine reassembly.
Common hand tools
Small cardboard boxes or plastic bags for
storing parts
Compartment-type metal box for storing
the hydraulic tappets (M40 engine)
Gasket scraper
Ridge reamer
Vibration damper puller
Micrometers
Telescoping gauges
Dial indicator set
Valve spring compressor
Cylinder surfacing hone
Piston ring groove cleaning tool
Electric drill motor
Tap and die set
Wire brushes
Oil gallery brushes
Cleaning solvent
8 Cylinder head- dismantling
4
1Remove the cylinder head (see Chapter 2A).
2Remove the oil supply tube from its
mounting on top of the cylinder head (see
illustrations). Note:It’s important to renew
the seals under the tube mounting bolts.
General engine overhaul procedures 2B•7
7.3 Engine left-hand mounting bracket -
M40 engine
8.2a Remove the oil tube from the top of
the cylinder head (M10 engine). Be sure to
note the location of all gaskets and
washers for reassembly
2B

7Wipe the oil out of the cylinder, and repeat
the procedure for the remaining cylinders.
8After the honing job is complete, chamfer
the top edges of the cylinder bores with a
small file, so the rings won’t catch when the
pistons are refitted. Be very careful not to nick
the cylinder walls with the end of the file.
9The entire engine block must be washed
again very thoroughly with warm, soapy
water, to remove all traces of the abrasive grit
produced during the honing operation. Note:
The bores can be considered clean when a
lint-free white cloth - dampened with clean
engine oil - used to wipe them out doesn’t
pick up any more honing residue, which will
show up as grey areas on the cloth.Be sure to
run a brush through all oil holes and galleries,
and flush them with running water.
10After rinsing, dry the block, and apply a
coat of light rust-preventive oil to all machined
surfaces. Wrap the block in a plastic bag to
keep it clean, and set it aside until
reassembly.
18 Pistons/connecting rods-
inspection
3
1Before the inspection process can be
carried out, the piston/connecting rod
assemblies must be cleaned and the original
piston rings removed from the pistons.Note:
Always use new piston rings when the engine
is reassembled.
2Using a piston ring refitting tool, carefully
remove the rings from the pistons. Be careful
not to nick or gouge the pistons in the
process (see illustration).
3Scrape all traces of carbon from the top of
the piston. A hand-held wire brush or a piece
of fine emery cloth can be used once the
majority of the deposits have been scraped
away. Do not, under any circumstances, use a
wire brush mounted in a drill motor to remove
deposits from the pistons. The piston material
is soft, and may be damaged by the wire
brush.
4Use a piston ring groove cleaning tool to
remove carbon deposits from the ring
grooves. Be very careful to remove only thecarbon deposits - don’t remove any metal,
and do not nick or scratch the sides of the
ring grooves (see illustration).
5Once the deposits have been removed,
clean the piston/rod assemblies with solvent,
and dry them with compressed air (if
available). Make sure the oil return holes in the
back sides of the ring grooves are clear.
6If the pistons and cylinder walls aren’t
damaged or worn excessively, and if the
engine block is not rebored, new pistons
won’t be necessary. Normal piston wear
appears as even vertical wear on the piston
thrust surfaces (90° to the gudgeon pin bore),
and slight looseness of the top ring in its
groove. New piston rings, however, should
always be used when an engine is rebuilt.
7Carefully inspect each piston for cracks
around the skirt, at the pin bosses, and at the
ring lands.
8Look for scoring and scuffing on the thrust
faces of the skirt, holes in the piston crown,
and burned areas at the edge of the crown. If
the skirt is scored or scuffed, the engine may
have been suffering from overheating and/or
abnormal combustion, which caused
excessively high operating temperatures. The
cooling and lubrication systems should be
checked thoroughly. A hole in the piston crown
is an indication that abnormal combustion (pre-
ignition) was occurring. Burned areas at the
edge of the piston crown are usually evidence
of spark knock (detonation). If any of the aboveproblems exist, the causes must be corrected,
or the damage will occur again. The causes
may include intake air leaks, incorrect fuel/air
mixture, or incorrect ignition timing. On later
vehicles with high levels of exhaust emission
control, including catalytic converters, the
problem may be with the EGR (exhaust gas
recirculation) system, where applicable.
9Corrosion of the piston, in the form of small
pits, indicates that coolant is leaking into the
combustion chamber and/or the crankcase.
Again, the cause must be corrected or the
problem may persist in the rebuilt engine.
10Measure the piston ring side clearance by
laying a new piston ring in each ring groove
and slipping a feeler gauge in beside it(see
illustration). Check the clearance at three or
four locations around each groove. Be sure to
use the correct ring for each groove - they are
different. If the side clearance is greater than
the figure listed in this Chapter’s Specifi-
cations, new pistons will have to be used.
11Check the piston-to-bore clearance by
measuring the bore (see Section 16) and the
piston diameter. Make sure the pistons and
bores are correctly matched. Measure the
piston across the skirt, at 90° to, and in line
with, the gudgeon pin (see illustration). (Any
difference between these two measurements
indicates that the piston is no longer perfectly
round.) Subtract the piston diameter from the
bore diameter to obtain the clearance. If it’s
greater than specified, the block will have to
be rebored, and new pistons and rings fitted.
2B•16 General engine overhaul procedures
18.11 Measure the piston diameter at a
90-degree angle to the gudgeon pin, at the
same height as the gudgeon pin
18.10 Check the ring side clearance with a
feeler gauge at several points around the
groove18.4 The piston ring grooves can be
cleaned with a special tool, as shown
here18.2 Removing the compression rings with
a ring expander - note the mark (arrowed)
facing up
If a groove cleaning tool isn’t available,
a piece broken off the old ring will do
the job, but protect your hands - piston
rings can be sharp

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

Warning: Do not remove the
pressure cap from the radiator or
expansion tank until the engine
has cooled completely and
there’s no pressure remaining in the
cooling system. Removing the cap from a
hot engine risks personal injury by
scalding.
Heating system
The heating system consists of a blower fan
and heater matrix located in the heater box,
with hoses connecting the heater matrix to the
engine cooling system, and the heater/air
conditioning control head on the dashboard.
Hot engine coolant is circulated through the
heater matrix passages all the time the engine
is running. Switching the heater on opens a
flap door to direct air through the heater
matrix, and the warmed air enters the
passenger compartment. A fan switch on the
control head activates the blower motor,
which forces more air through the heater
matrix, giving additional heater output for
demisting, etc.
Air conditioning system
The air conditioning system consists of a
condenser mounted in front of the radiator, an
evaporator mounted adjacent to the heater
matrix, a compressor mounted on the engine,
a filter-drier (receiver-drier) which contains a
high-pressure relief valve, and the plumbing
connecting all of the above components.
A blower fan forces the warmer air of the
passenger compartment through the
evaporator matrix (a radiator-in-reverse),
transferring the heat from the air to the
refrigerant. The liquid refrigerant boils off into
low-pressure vapour, taking the heat with it
when it leaves the evaporator.
Note: Refer to the precautions at the start
of Section 12 concerning the potential
dangers associated with the air conditioning
system.
2 Antifreeze-
general information
Warning: Do not allow antifreeze
to come in contact with your skin
or painted surfaces of the
vehicle. Rinse off spills
immediately with plenty of water. If
consumed, antifreeze can be fatal;
children and pets are attracted by its
sweet taste, so wipe up garage floor and
drip pan coolant spills immediately. Keep
antifreeze containers covered, and repair
leaks in your cooling system as soon as
they are noticed.
The cooling system should be filled with a
60/40% water/ethylene-glycol-based anti-
freeze solution, which will prevent freezing
down to approximately -27°C (-17°F). The
antifreeze also raises the boiling point of thecoolant, and (if of good quality) provides
protection against corrosion.
The cooling system should be drained,
flushed and refilled at the specified intervals
(see Chapter 1). Old or contaminated
antifreeze solutions are likely to cause
damage, and encourage the formation of rust
and scale in the system. Use distilled water
with the antifreeze, if available, or clean
rainwater. Tap water will do, but not if the
water in your area is at all “hard”.
Before adding antifreeze, check all hose
connections, because antifreeze tends to
search out and leak through very minute
openings. Engines don’t normally consume
coolant, so if the level goes down, find the
cause and correct it.
The antifreeze mixture should be
maintained at its correct proportions; adding
too much antifreeze reduces the efficiency of
the cooling system. If necessary, consult the
mixture ratio chart on the antifreeze container
before adding coolant. Hydrometers are
available at most car accessory shops to test
the coolant. Use antifreeze which meets the
vehicle manufacturer’s specifications.
3 Thermostat-
check and renewal
1
Warning: Do not remove the
radiator cap, drain the coolant, or
renew the thermostat until the
engine has cooled completely.
Check
1Before assuming the thermostat is to blame
for a cooling system problem, check the
coolant level, drivebelt tension (see Chapter 1)
and temperature gauge (or warning light)
operation.
2If the engine seems to be taking a long time
to warm up (based on heater output or
temperature gauge operation), the thermostat
is probably stuck open. Renew the
thermostat.
3If the engine runs hot, use your hand to
check the temperature of the upper radiator
hose. If the hose isn’t hot, but the engine is,
the thermostat is probably stuck closed,preventing the coolant inside the engine from
circulating to the radiator. Renew the
thermostat.
Caution: Don’t drive the vehicle
without a thermostat. The engine
will be very slow to warm-up in
cold conditions, resulting in poor
fuel economy and driveability. A new
thermostat is normally an inexpensive
component anyway.
4If the upper radiator hose is hot, it means
that the coolant is flowing and the thermostat
is at least partly open. Consult the “Fault
finding” Section at the rear of this manual for
cooling system diagnosis.
Renewal
All models
5Disconnect the negative cable from the
battery.
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.
6Drain the cooling system (see Chapter 1). If
the coolant is relatively new or in good
condition, save it and re-use it.
M10 engines
7The thermostat is located in the bottom
hose. First remove the cooling fan.
8Note the fitted position of the thermostat,
then unscrew the hose clamps and withdraw
the thermostat from the hose connections
(see illustration).
9Refit the thermostat-to-hose connections,
and tighten the hose clamps.
10Refit the cooling fan.
M20 and M30 engines
11Loosen the hose clamp (see illustration),
then detach the hose(s) from the thermostat
cover.
3•2 Cooling, heating and air conditioning systems
3.11 On M20 and M30 engine models,
loosen the hose clamp (A) and disconnect
the hose from the thermostat housing
cover - note that the coolant temperature
sender unit (barely visible behind the fuel
pressure regulator) is located at the top of
the thermostat housing (B)
3.8 On the M10 (four-cylinder) engine, the
thermostat (arrowed) is connected in-line
in the radiator hose

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

4
Carburettor (Solex 2B4)
Main jet
Stage 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . X120
Stage 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . X90
Air correction jet
Stage 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135
Stage 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75
Venturi diameter
Stage 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 mm
Stage 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 mm
Idle/air jet
Stage 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50/120
Stage 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40/125
Float needle valve diameter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.0 mm
Choke gap (pulldown) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.0 to 5.5 mm
Throttle positioner spring preload . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22.0 to 24.0 mm
Float level
Stage 1 float chamber . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27.0 to 29.0 mm
Stage 2 float chamber . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29.0 to 31.0 mm
Chapter 4 Fuel and exhaust systems
Accelerator cable - check, adjustment and renewal . . . . . . . . . . . . . 9
Air cleaner assembly - removal and refitting . . . . . . . . . . . . . . . . . . . 8
Air filter renewal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . See Chapter 1
Airflow meter - check, removal and refitting . . . . . . . . . . . . . . . . . . . 16
Carburettor - cleaning and adjustment . . . . . . . . . . . . . . . . . . . . . . . 12
Carburettor - general information . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Carburettor - removal and refitting . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Cold start injector and thermotime switch -
checkand renewal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Engine idle speed check and adjustment . . . . . . . . . See Chapter 1
Exhaust system check . . . . . . . . . . . . . . . . . . . . . . . . See Chapter 1
Exhaust system servicing - general information . . . . . . . . . . . . . . . . 22
Fuel filter renewal . . . . . . . . . . . . . . . . . . . . . . . . . . . See Chapter 1
Fuel injection system - check . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Fuel injection system - depressurising . . . . . . . . . . . . . . . . . . . . . . . 2Fuel injection system - fault finding . . . . . . . . . . . . See end of Chapter
Fuel injection - general information . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Fuel injection systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Fuel injectors - check and renewal . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Fuel lines and fittings - repair and renewal . . . . . . . . . . . . . . . . . . . . 5
Fuel pressure regulator - check and renewal . . . . . . . . . . . . . . . . . . 18
Fuel pump, transfer pump and fuel level sender unit -
removal and refitting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Fuel pump/fuel pressure - check . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Fuel system check . . . . . . . . . . . . . . . . . . . . . . . . . . . See Chapter 1
Fuel tank - removal and refitting . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Fuel tank cleaning and repair - general information . . . . . . . . . . . . . 7
General information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Idle air stabiliser valve - check, adjustment and renewal . . . . . . . . . 21
Throttle body - check, removal and refitting . . . . . . . . . . . . . . . . . . . 17
4•1
Easy,suitable for
novice with little
experienceFairly easy,suitable
for beginner with
some experienceFairly difficult,
suitable for competent
DIY mechanic
Difficult,suitable for
experienced DIY
mechanicVery difficult,
suitable for expert
DIY or professional
Degrees of difficulty
Specifications Contents

Carburettor (Solex 2BE)
Main jet
Stage 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . X120
Stage 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . X110
Air correction jet
Stage 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 140
Stage 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
Venturi diameter
Stage 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 mm
Stage 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 mm
Idle fuel jet
Stage 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47.5 mm
Idle air jet
Stage 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 180
Float needle valve diameter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.0 mm
Throttle positioner coil resistance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.97 to 1.63 ohms
Intake air temperature resistance
-10º C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8200 to 10 500 ohms
20º C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2200 to 2700 ohms
80º C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 300 to 360 ohms
Float level
Stage 1 float chamber . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27.0 to 29.0 mm
Stage 2 float chamber . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29.0 to 31.0 mm
Fuel pressure checks (carburettor engines)
Fuel pump delivery pressure (engine idling) . . . . . . . . . . . . . . . . . . . . . . 0.1 to 0.3 bars
Fuel pressure checks (fuel injection engines)
Fuel system pressure (relative to intake manifold pressure)
3-Series (E30)
316i with M40/B16 engine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.0 ± 0.06 bars
318i with M10/B18 engine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.5 to 3.0 bars
318i with M40/B18 engine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.0 ± 0.06 bars
320i with M20/B20 engine (L-Jetronic) . . . . . . . . . . . . . . . . . . . . . . 2.5 to 3.0 bars
320i with M20/B20 engine (Motronic) . . . . . . . . . . . . . . . . . . . . . . . 2.5 ± 0.05 bars
325i with M20/B25 engine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.0 ± 0.05 bars
5-Series (E28/”old-shape”)
All models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.5 to 3.0 bars
5-Series (E34/”new-shape”)
518i with M40/B18 engine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.0 ± 0.06 bars
All other models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.5 to 3.0 bars
Fuel system hold pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.1 bars
Fuel pump maximum pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.3 to 6.9 bars
Fuel pump hold pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.5 bars
Transfer pump pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.28 to 0.35 bars
Injectors
Injector resistance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14.5 to 17.5 ohms
Accelerator cable free play . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.0 mm
Torque wrench settingsNm
Carburettor mountings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Fuel pump to cylinder head . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Throttle body nuts/bolts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 to 26
4•2 Fuel and exhaust systems
1 General information
With the exception of early models (316 and
518 models) all engines are equipped with
electronic fuel injection.
Early 316 and 518 models are equipped
with Solex carburettors. The carburettor fitted
is either a Solex 2B4 (early models) or
2BE (later models). The mechanical fuel pumpis driven by an eccentric lobe on the
camshaft.
Fuel injection models are equipped with
either the L-Jetronic or the Motronic fuel
injection system. From 1988, fuel injection
models are equipped with an updated version
of the Motronic system - this system is easily
distinguished from the earlier system by the
absence of a cold start injector. The electric
fuel pump is located beneath the rear of the
vehicle, or inside the fuel tank. The fuel pump
relay on Motronic systems is activated from aearth signal from the Motronic control unit
(ECU). The fuel pump operates for a few
seconds when the ignition is first switched on,
and it continues to operate only when the
engine is actually running.Air intake system
The air intake system consists of the air
filter housing, the airflow meter and throttle
body (fuel injection models), and the intake
manifold. All components except the intake
manifold are covered in this Chapter; for

information on removing and refitting the
intake manifold, refer to Chapter 2A.
The throttle valve inside the throttle body or
carburettor is actuated by the accelerator
cable. When you depress the accelerator
pedal, the throttle plate opens and airflow
through the intake system increases.
On fuel injection systems, a flap inside the
airflow meter opens wider as the airflow
increases. A throttle position switch attached
to the pivot shaft of the flap detects the angle
of the flap (how much it’s open) and converts
this to a voltage signal, which it sends to the
computer.
Fuel system
On carburettor models, the fuel pump
supplies fuel under pressure to the
carburettor. A needle valve in the float
chamber maintains the fuel at a constant
level. A fuel return system channels excess
fuel back to the fuel tank.
On fuel injection models, an electric fuel
pump supplies fuel under constant pressure
to the fuel rail, which distributes fuel to the
injectors. The electric fuel pump is located
inside the fuel tank on later models, or beside
the fuel tank on early models. Early models
also have a transfer pump located in the fuel
tank. The transfer pump acts as an aid to the
larger main pump for delivering the necessary
pressure. A fuel pressure regulator controls
the pressure in the fuel system. The fuel
system also has a fuel pulsation damper
located near the fuel filter. The damper
reduces the pressure pulsations caused by
fuel pump operation, and the opening and
closing of the injectors. The amount of fuel
injected into the intake ports is precisely
controlled by an Electronic Control Unit (ECU
or computer). Some later 5-Series models
have a fuel cooler in the return line.
Electronic control system (fuel
injection system)
Besides altering the injector opening
duration as described above, the electronic
control unit performs a number of other tasks
related to fuel and emissions control. It
accomplishes these tasks by using data
relayed to it by a wide array of information
sensors located throughout the enginecompartment, comparing this information to
its stored map, and altering engine operation
by controlling a number of different actuators.
Since special equipment is required, most
fault diagnosis and repair of the electronic
control system is beyond the scope of the
home mechanic. Additional information and
testing procedures for the emissions system
components (oxygen sensor, coolant
temperature sensor, EVAP system, etc.) is
contained in Chapter 6.
2 Fuel injection system-
depressurising
1
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.
1Remove the fuel pump fuse from the main
fuse panel (see illustrations). Note:Consult
your owner’s handbook for the exact location
of the fuel pump fuse, if the information is not
stamped onto the fusebox cover.
2Start the engine, and wait for it to stall.
Switch off the ignition.
3Remove the fuel filler cap to relieve the fuel
tank pressure.
4The fuel system is now depressurised.
Note:Place a rag around fuel lines before
disconnecting, to prevent any residual fuel
from spilling onto the engine(see
illustration).
5Disconnect the battery negative cable
before working on any part of the 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. 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.
3 Fuel pump/fuel pressure-
check
3
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.
Carburettor engines
1To test the fuel pump, it will be necessary to
connect a suitable pressure gauge between
the fuel pump outlet, and the carburettor
supply pipe. For this particular test, the fuel
return valve, which is normally connected in
the fuel line from the fuel pump to the
carburettor, mustbe bypassed.
2With the engine running at idle speed, the
pump pressure should be between 0.1 and
0.3 bars.
3Should a pressure gauge not be available, a
simpler (but less accurate) method of testing
the fuel pump is as follows.
4Disconnect the outlet hose from the fuel
pump.
5Disconnect the LT lead from the coil, to
prevent the engine firing, then turn the engine
over on the starter. Well-defined spurts of fuel
should be ejected from the outlet hose.
Fuel injection engines
Note 1:The electric fuel pump is located
inside the fuel tank on later models, or beside
the fuel tank on early models. Early models are
also equipped with a transfer pump located in
the fuel tank. The transfer pump feeds the
main pump, but can’t generate the high
pressure required by the system.
Note 2:The fuel pump relay on Motronic
systems is activated by an earth signal from
the Motronic control unit (ECU). The fuel
pump operates for a few seconds when the
ignition is first switched on, and then
continues to operate only when the engine is
actually running.
Fuel and exhaust systems 4•3
2.4 Be sure to place a rag under and
around any fuel line when disconnecting2.1b Removing the fuel pump fuse on
5-Series models2.1a Removing the fuel pump fuse on
3-Series models
4