Compression Check: Testing and Inspection

Notes:
Test compression pressure at normal operating temperature.
If the minimum compression pressure is not reached, test cylinder leakage.
Unscrew all the spark plugs for testing.
Turn crankshaft with starter and compression pressure recorder.

WARNING
The engines are equipped with an ignition system with variable ignition characteristics (EZL).
Because of high ignition voltage, it is very dangerous to touch components of the ignition system (ignition coil, ignition cables, spark plug connector, plug-on unit) when
^ The engine is running
^ The engine is started
^ The key in the steering lock is in position 2 and the engine is cranked by hand.





1 Switch off ignition. Detach connector from ignition distributor pickup (green cable on control module) (arrow).





Caution:
On injection engines, detach the fuel pump relay module (N16/4) before turning the crankshaft to ensure that no fuel is injected.





2 Connect compression pressure recorder. This is done by clamping one of the two alligator clamps (arrow) of the compression pressure recorder, Part No. 001 589 76 21 00, to the positive terminal post of the battery.





3 Detach connector (X27) from plug connection (terminal 50).
4 Plug in connector of adapter cable (01), Part No. 124 589 36 63 00.
5 Crank engine several times with starter motor, in idle position, selector lever in position "P", and parking brake applied so that residues and soot are ejected.





6 To test each cylinder, press the compression pressure recorder into the spark plug hole of the particular cylinder and, with the throttle valve fully opened, crank engine approx. 8 revolutions. Test all the cylinders in this way.
- Specified Value: 9.0 - 10.0 bar (130 - 145 psi)
- Minimum Value: Approx. 7.5 bar (109 psi)
- Permissible difference between cylinders: 3.0 bar (43.5 psi) max.
7 Blow out spark plug recesses with compressed air. Remove any residues on the tapered sealing seat.