1984 BMW 3 SERIES fuel pump

detach them. Pieces of masking tape with
numbers or letters written on them work well
(see illustration).
6Label and detach all coolant hoses from the
engine (see Chapter 3).
7Remove the cooling fan, shroud and
radiator (see Chapter 3). Note:On the M40
engine, it is only necessary to remove the
cooling fan and shroud; however, prevent
damage to the radiator by covering it with a
piece of wood or cardboard.
8Remove the drivebelts (see Chapter 1).
9Disconnect the fuel lines from the fuel rail
(see Chapter 4).
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, and 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.
10Disconnect the accelerator cable (see
Chapter 4) and kickdown linkage/speed
control cable (see Chapter 7B), if applicable,
from the engine.
11Where fitted, unbolt the power steering
pump (see Chapter 10). Leave the lines/hoses
attached, and make sure the pump is kept in
an upright position in the engine compartment
(use wire or rope to restrain it out of the way).
12On air-conditioned models, unbolt the
compressor (see Chapter 3) and set it aside,
or tie it up out of the way. Do not disconnect
the hoses.
13Drain the engine oil (see Chapter 1) and
remove the filter. Remove the engine splash
guard from under the engine.
14Remove the starter motor (see Chapter 5).15Remove the alternator (see Chapter 5).
This is not essential on all models, but it is a
good idea in any case to avoid accidental
damage.
16Unbolt the exhaust system from the
engine (see Chapter 4).
17If you’re working on a vehicle with an
automatic transmission, remove the torque
converter-to-driveplate fasteners (see
Chapter 7B). On the M40 engine, unbolt the
automatic transmission fluid coolant pipes
from the sump.
18Support the transmission with a jack.
Position a block of wood between them, to
prevent damage to the transmission. Special
transmission jacks with safety chains are
available - use one if possible.
19Attach an engine sling or a length of chain
to the lifting brackets on the engine. If the
brackets have been removed, the chain can
be bolted directly to the intake manifold studs,
but place a flat washer between the chain and
the nut, and tighten the nut all the way up to
the chain, to avoid the possibility of the studs
bending.
20Roll the hoist into position and connect
the sling to it. Take up the slack in the sling or
chain, but don’t lift the engine.
Warning: DO NOT place any part
of your body under the engine
when it’s supported only by a
hoist or other lifting device.
21On M10, M20 and M30 engines, remove
the transmission rear crossmember, and
slightly lower the rear of the transmission.
22Remove the transmission-to-engine block
bolts using a Torx socket. Note:The bolts
holding the bellhousing to the engine block
will require a swivel at the socket, and a very
long extension going back towards the
transmission.
23Remove the engine mounting-to-frame
bracket nuts. On the M40 engine, unbolt the
dampers from the mountings.
24Recheck to be sure nothing is still
connecting the engine to the transmission or
vehicle. Disconnect anything still remaining.
25Raise the engine slightly. Carefully work it
forwards to separate it from the transmission.
If you’re working on a vehicle with an
automatic transmission, you may find the
torque converter comes forward with theengine. If it stays with the transmission, leave
it, but you may find it easier to let it come
forward until it can be grasped easier and be
pulled from the crankshaft. Note:When
refitting the torque converter to the
transmission before the engine is refitted, be
sure to renew the transmission front pump
seal, which will probably be damaged when
the converter comes out with the engine.
Either method is acceptable, but be prepared
for some fluid to leak from the torque
converter if it comes out of the transmission. If
you’re working on a vehicle with a manual
transmission, draw the engine forwards until
the input shaft is completely disengaged from
the clutch. Slowly raise the engine out of the
engine compartment. Check carefully to make
sure everything is disconnected.
26Remove the flywheel/driveplate (and
where applicable, the engine rear plate), and
mount the engine on an engine stand (see
illustration). Do not turn the M40 engine
upside-down (see Cautionin Section 4).
Refitting
27Check the engine and transmission
mountings. If they’re worn or damaged, renew
them.
28Refit the flywheel or driveplate (see
Chapter 2A). If you’re working on a manual
transmission vehicle, refit the clutch and
pressure plate (see Chapter 7A). Now is a
good time to fit a new clutch.
29If the torque converter came out with the
engine during removal, carefully refit the
converter into the transmission before the
engine is lowered into the vehicle.
30Carefully lower the engine into the engine
compartment - make sure the engine
mountings line up.
31If you’re working on an automatic
transmission vehicle, guide the torque
converter onto the crankshaft following the
procedure outlined in Chapter 7B.
32If you’re working on a manual
transmission vehicle, apply a dab of high-
melting-point grease to the input shaft, and
guide it into the clutch and crankshaft pilot
bearing until the bellhousing is flush with the
engine block.. Do not allow the weight of the
engine to hang on the input shaft.
33Refit the transmission-to-engine bolts,
and tighten them securely.
Caution: DO NOT use the bolts to
force the transmission and
engine together.
34Refit the remaining components in the
reverse order of removal.
35Add coolant, oil, power steering and
transmission fluid as needed.
2B•6 General engine overhaul procedures
5.26 Removing the engine rear plate -
M40 engine5.5 Label each wire before unplugging the
connector
If there’s any possibility of
confusion, make a sketch of
the engine compartment and
clearly label the lines, hoses
and wires.
It may be necessary to rock
the engine slightly, or to turn
the crankshaft, to allow the
input shaft splines to mate
with the clutch plate

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

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

Note 3:The following checks assume the fuel
filter is in good condition. If you doubt the
condition of your fuel filter, renew it (see
Chapter 1).
Note 4:In order to get accurate test results, it
is recommended that the fuel pressure be
checked from both the main fuel pump and
transfer pump where applicable.
Fuel pump/transfer pump operational
check
6Bridge the connector terminals that
correspond to the fuel pump relay pins 30 and
87b (L-Jetronic systems) or 30 and 87
(Motronic systems) with a suitable jumper wire
(see illustrations).
7Have an assistant switch the ignition on
while you listen at the fuel tank. You should
hear a whirring sound for a couple of seconds.
Note:This test applies to the transfer pump
also. If there is no whirring sound, there is a
problem in the fuel pump circuit. Check the
fuel pump main fuse and relay first (see
Chapter 12). If the main relay is OK, test the
fuel pump relay.
Fuel system pressure check8Depressurise the fuel system (see Section 2).
9Detach 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 codebefore 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.
10Detach the fuel feed line from the fuel rail
on L-Jetronic (see illustration)and early
Motronic systems, or from the fuel filter to the
main fuel line on later Motronic systems.
11Using a tee-piece (three-way fitting), a
short section of high-pressure fuel hose and
clamps, attach a fuel pressure gauge without
disturbing normal fuel flow (see illustration).
Warning: Do not use a plastic tee
fitting for this test. It won’t be
able to withstand the fuel system
pressure.
12Reconnect the battery.
13Bridge the terminals of the fuel pump
relay using a jumper wire.
14Turn the ignition switch on.
15Note the fuel pressure, and compare it
with the pressure listed in this Chapter’s
Specifications.
16If the system fuel pressure is less than
specified:
a) Check the system for fuel leaks. Repair
any leaks found, and recheck the fuel
pressure.b) If there are no leaks, fit a new fuel filter
and recheck the fuel pressure.
c) If the pressure is still low, check the fuel
pump pressure (see below) and the fuel
pressure regulator (see Section 18).
17If the pressure is higher than specified,
check the fuel return line for an obstruction. If
the line is not obstructed, renew the fuel
pressure regulator.
18Turn the ignition off, wait five minutes and
look at the gauge. Compare the reading with
the system hold pressure listed in this
Chapter’s Specifications. If the hold pressure
is less than specified:
a) Check the system for fuel leaks. Repair
any leaks found, and recheck the fuel
pressure.
b) Check the fuel pump pressure (see
below).
c) Check the fuel pressure regulator (see
Section 18).
d) Check the injectors (see Section 20).
Fuel pump pressure check
Warning: For this test, a fuel
pressure gauge with a bleed
valve will be needed, in order to
relieve the high fuel pressure
safely. After the test is completed, the
normal procedure for depressurising will
not work, because the gauge is connected
directly to the fuel pump.
4•4 Fuel and exhaust systems
3.10 Disconnect the fuel feed line
(arrowed) from the fuel rail (L-Jetronic
system shown) . . .3.6d . . . then, use a jumper wire to bridge
the terminals on the connector that
correspond to fuel pump relay pins 30 and
87
3.6c On all 1989 and later models, remove
the four bolts and the protective cover to
gain access to the fuel pump relay and
ECU . . .3.6b On Motronic systems, use a jumper
wire to bridge the terminals on the
connector that correspond to the fuel
pump relay pins 30 and 873.6a On L-Jetronic systems, use a jumper
wire to bridge the terminals on the
connector that correspond to the fuel
pump relay pins 30 and 87b
3.11 . . . and connect the gauge between
the fuel feed line and the fuel rail using a
tee-piece fitting

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