Fault Diagnosis, Ignition Misfiring

FAULT DIAGNOSIS, IGNITION - MISFIRING

Symptom of fault
Misfiring in any cylinder

Diagnostic procedure
1. Connect an ISAT scan tool

- Ignition switched ON.
- Select each individual ignition coil in the ISAT menu "ACTIVATE" with the submenu "IGNITION COILS".

Activation of an ignition coil takes place for 10 seconds at 200 Hz. If a longer activation time is required, the command must be repeated.

- Listen for the sound of each individual ignition coil operating.
- If all the ignition coils are working, continue with step 4.
- If any ignition coil is not working, continue with step 2.





2. With the ignition switched OFF, unplug the 10-pole connector of the [1][2]ignition discharge module.

- Ignition switched ON.
- Connect the test lamp between pin 10 and the trigger cable of the relevant ignition coil.
- Activate the ignition coil concerned with the ISAT command.

The test lamp must light up with extremely short interuptions for 10 seconds. In the event of uncertainty, repeat the command.

- If the test lamp lights up with extremely short interuptions, install a new [1][2]ignition discharge module.
- If the test lamp does not light up or lights up with a steady glow, continue with step 3.





3. Check the relevant trigger cable for continuity/shorting.

- If the cable is OK, continue at "Procedure before replacing ECM".





4. Check the operation of the [1][2]ignition discharge module.

- Disconnect the [1][2]ignition discharge module from the camshaft cover.
- Install a test spark plug (part no. 86 11 386) in the spark plug connection concerned.
- Ground the spark plug with cable 8610867.
- Activate each individual ignition coil with an ISAT scan tool.
- Check that a spark is produced on the activated spark plug.
- If no spark is produced, install a new [1][2]ignition discharge module.
- If a spark is produced, install a new spark plug.

5. Drive the car to check whether the fault symptoms persist. If so, continue at "Procedure before replacing ECM".

CAUTION: The [1][2]ignition discharge module must be positioned with the ignition coils facing down during the test so that the transformer oil is insulating the high-voltage part of the ignition coils.

WARNING: HIGH VOLTAGE. The electronic ignition system generates voltages of 40,000 Volts. 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.