BMW 3 (E46). Manual — part 50

Reconnect battery.

CAUTION!

To prevent damaging engine
electronic systems, install all ground
wires previously removed, including
the ground wires for the ignition
coils.

Tightening torques

Coolant drain plug
to cylinder block

25 Nm (18 ft-lb)

Radiator cooling
fan to coolant
pump

40 Nm (30 ft-lb)

Radiator drain
screw to radiator

2.5 Nm (22 in-lb)

Spark plug to
cylinder head

25 Nm (18 ft-lb)

113-4

Diagnostic Testing

Cylinder compression,
checking

A compression gauge is needed to
make a compression test. For accurate
test, the battery and starter must be
capable of cranking the engine at least
300 rpm, and the engine should be at
normal operating temperature.

Note:

Performing a compression test may
cause a fault to set in the ECM and
may illuminate the engine service light.
The light can only be turned out using
either BMW special service scan tools
or an equivalent aftermarket scan tool.
Disconnecting the battery will not erase
the fault memory nor turn out the light.

Disable ignition system by removing
DME main relay (arrow) from the
electronics box (E-box) in left rear of
engine compartment

WARNING!

The ignition system produces
high voltages that can be fatal.
Avoid contact with exposed
terminals and use extreme
caution when working on a car
with the ignition switched on or
the engine running.

Do not touch or disconnect
ignition components while the
engine is running or being
cranked by the starter.

CAUTION!

Failure to remove the DME main
relay or attempting to disable the
ignition system by other methods
may result in damage to the engine
control module (ECM).

Remove housing for interior ventilation
microfilter.

Remove upper cover and
microfilter.

Open wiring harness loom cover
(A) and remove wires.

Unfasten screws (B) and remove
lower microfilter housing.

-

Remove oil filler cap.

-

Remove engine cover over ignition
coils. Replace oil filler cap.

Remove ignition coils.

Pull up on spring clips to
disconnect ignition coil harness
connectors.

Remove coil grounding straps.

Remove coils.

Remove spark plugs.

Note:

Check the spark plugs for oil deposits
that may indicate poor cylinder sealing,
then set them aside in order. Used
spark plugs should be reinstalled in the
same cylinder from which they were

removed.

Install compression gauge in first
cylinder's spark plug hole, tight
enough to form a good seal.

-

With parking brake set,
transmission in PARK or
NEUTRAL, and accelerator pedal
pressed to floor, crank engine with
starter. Record highest value
indicated by gauge.

Note:

The compression gauge reading
should increase with each
compression stroke and reach
near its maximum reading in about
4-6 strokes.

All cylinders should reach
maximum compression in the
same number of strokes. If a
cylinder needs significantly more
strokes to reach maximum
compression, there is a problem.

-

Release pressure at compression
gauge valve, then remove gauge
from spark plug hole. Repeat test
for each cylinder and compare
results with values given below.

Compression pressures

Minimum

10 - 11 bar

(142 - 156 psi)

Maximum
difference between
cylinders

0.5 bar (7 psi)

-

Compression readings may be
interpreted as follows: