Detonation Retard

Knock sensors consist of piezoelectric crystals encased in metal and plastic housings located on each cylinder head, under intake manifold. Vibrations in engine cause crystal to generate small amounts of voltage. This voltage signal is used by PCM to determine necessary timing retardation.

One knock sensor is installed on each head under intake manifold. Using 2 knock sensors makes it possible for system to be more accurate and responsive.

When knocking occurs, ignition timing is retarded until knocking is eliminated. Since engine knock limits vary from cylinder to cylinder, knock regulation is cylinder selective.

Knock control starts when coolant temperature is 104°F (40°C) or above. Ignition angle of knocking cylinder is retarded in steps to a maximum of 12 degrees or until knocking stops.

If cylinder knock continues, PCM will switch from premium fuel ignition map to ignition map for regular fuel. This allows ignition timing to be retarded up to 3 additional degrees.