Engine Does Not Run on All Cylinders

Engine does not run on all cylinders

WARNING: The electrical ignition system generates voltage 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.

Fault symptom

Engine does not run on all cylinders.


Diagnostic procedure




1 Identification of faulty cylinder

- Start the engine and run it at idling speed.

- Turn off one injector at a time to identify the faulty cylinder. To turn off an injector, unplug its connector.

- Listen to the sound of the engine to determine which cylinder is faulty.

- Continue with point 2.




2 Check the ignition discharge module

- Remove the ignition discharge module from the camshaft cover.

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

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

Are sparks obtained?
YES Continue with point 3.
NO Continue fault diagnosis as described in "Ignition - misfiring".

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.




3 Check the compression

- Carry out a compression test on the cylinder concerned.

Compression test OK?
YES Change the spark plug and try to start the engine. If the fault symptom persists, continue fault diagnosis as described "Fuel Injector". [1][2]Checking Injector Flow Capacity
NO Determine compression failure.

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 slide-out of the pins in the ignition discharge module's 10 pin connector does not occur when the connector is plugged into the module.