Ignition - Misfiring

Ignition - misfiring


Fault symptom

Misfiring in one of the cylinders.


WARNING:
The electrical ignition system generates voltages of 40,000 V. Such voltages may be fatal to persons with a weak heart or those who have a pacemaker implant. In view of this, treat the ignition system with the respect it deserves.

Important: The ignition discharge module should be stood with the ignition coils facing downwards when testing is performed so that the transformer oil will provide good insulation in the high-tension part of the coils.


Diagnostic procedure




1 Check the operation of the ignition coils

- Remove the ignition discharge module from the camshaft cover.

- Remove the fuel pump fuse (14).

- Fit test spark plugs 86 11 386 in the spark plug connections. Ground the spark plugs with cable assembly 86 10 867.

- Activate with SAT scan tool command code 450 or run the starter motor.

- Check that the springs pressing on the spark plugs are in place and that the rubber seals are intact.

All ignition coils in working order?
YES Change the spark plugs.
NO Continue with point 2.







2 Check the performance of the ignition coil

- Unplug the ignition discharge module's 10-pin connector or connector 123/H4-9.

- Ignition switch in the ON position.

- Connect test tamp 86 11 857 between battery voltage or pin 10 and the trigger lead of the relevant ignition coil, see table below.

- Activate the ignition coils with ISAT command code 450 or run the starter motor.

The test lamp should light up and flicker extremely briefly. In case of uncertainty, repeat the command.

Does the test lamp light up and flicker briefly?
YES Change the ignition discharge module.
NO Continue with point 3.







3 Check the trigger lead

- Check the trigger lead in question for continuity, see table below.

- Check the lead for open circuit and shorting.

Is the lead OK?
YES Continue with the final check, point 4.
NO Rectify the fault.

Note: The pins in connector 123/H4-9/H4-10 may have lost their springiness with poor contact and unreliable operation as a result. Check one pin at a time and rectify any defects.
Also check that slid-out of the pins in the ignition discharge module's 10-pin connector does not occur when the connector is plugged into the module.




4 Final check

- Implementation of driving cycle:
Drive the car at varying engine loads and rpm for 5 minutes.

- Evaluation of driving cycle:

Does the fault recur?
YES Continue with "Before Control Module Replacement". Service and Repair
NO The steps taken to rectify the fault were correct.