Engine management system - V8 (Spark plugs): Description and operation

Spark plugs

The spark plugs are platinum tipped on both centre and earth electrodes. The platinum tips give a long maintenance free life.

Cleaning or resetting the spark plug gap is not recommended as this could result in damaging the platinum tips and thereby reducing reliability.

The misfire detection system will malfunction and store erroneous codes if the incorrect spark plugs are used.

Input/Output The ignition coils provide a voltage to the spark plugs via the ht leads. The cylinder head via the individual thread of each spark plug provides the earth path.

The spark plugs can fail in the following ways: l Faulty component. l Connector or wiring fault. l Breakdown of high tension lead causing tracking to chassis earth. l Incorrect spark plugs fitted.

In the event of a spark plug failure, misfire on specific cylinder may be observed:

High tension (ht) leads

The ht leads are located on top of the engine, below the plenum chamber. Their function is to transfer the ht voltage generated by the ignition coils to the spark plugs in the engine.

Input/Output The input to the ht lead is ht voltage from the ignition coil pack. The ht lead then supplies this voltage to the spark plug. Output ht voltage is used by the spark plugs to ignite the air/fuel mixture in the combustion chamber.

The ht leads can fail in the following ways: l Connector/ Wiring fault. l Faulty component causing spark tracking to chassis earth. l Damage to ht leads during component removal.

In the event of a ht lead failure the following symptom may be observed: l Misfire on specific cylinder.

All ignition system related faults are diagnosed by the misfire detection system and its fault codes.