Ignition - Misfiring

WARNING: The electronic ignition system generates voltages of 40,000 V. This voltage can prove fatal to people with weak hearts or those who are fitted with pacemakers. The ignition system should therefore be treated with great respect.







FAULT DIAGNOSIS, IGNITION - MISFIRING

Fault symptom
Misfiring in one of the cylinders Diagnostic procedure

1. Checking the operation of the ignition coils
Connect the Scan Tool.
Ignition switch in the ON position.
Select "ACTIVATE".
Select "IGNITION COILS"
Select "IGNITION CYL1", "CYL2", "CYL3" AND "CYL4". Each individual ignition coil must be selected separately.
An ignition coil is activated for 10 seconds at 200 Hz. For longer activation the command must be repeated.
Listen for the sound of each ignition coil working.

If all the ignition coils am working, continue with point 4.

If any ignition coil is not working, continue with point 2.






2. Checking the operation of the ignition coils
Unplug the ignition discharge module's 10-pin connector.
Ignition switch in the ON position.
Connect the test lamp to pin 10 and the trigger lead of the ignition coil in question see table below. Then activate the ignition coil concerned by means of a Scan Tool command.

Trigger lead cylinder 10-pin connector,
No. No.
1 2
2 3
3 4
4 5

The test lamp should light up for 10 seconds and go out for extremely brief instants during this time. If there is any uncertainty repeat the command.

If the test lamp lights up and goes out for extremely brief instants, change the ignition discharge module.

If the test lamp does not light up or lights up continuously, continue with point 3.





3. Checking The Trigger Lead
Check the trigger lead concerned for continuity, see table.
Check the lead for continuity/shorting.





If the wiring is OK, continue with point 5.

If the wiring is not OK, rectify the fault.

IMPORTANT:The ignition discharge module must be positioned with the ignition coils facing downwards during the test to ensure that the transformer oil effectively insulates the high-tension part of the ignition coils.





4. Checking The Operation Of The Ignition Discharge Module
Detach the ignition discharge module from the camshaft cover.
Fit test spark plugs (part No. 86 11 386) in the ignition discharge module. Ground the spark plugs with cable 86 10 867. Activate each individual ignition coil by means of the Scan Tool. Check that each activated spark plug produces a spark.

If a spark is produced, change the spark plug.

If no spark is produced, change the ignition discharge module.

5. Final Check
Drive the car on test and check whether the fault symptom persists. If it does, refer to Before Replacing A Control Module.