Knock Sensor
Knock sensors consist of piezoelectric crystals encased in metal and plastic housings located on crankcase. Vibrations in engine cause crystal to generate small amounts of voltage. This voltage signal is used by ECM to determine necessary timing retardation.
Knock sensors are bolted to engine block under intake manifold. See Fig 1 . Using 2 sensors makes it possible for ECM to sense cylinder knock more accurately. On 1.8L engines KS I is located adjacent to cylinders No. 1 and 2. KS II is located adjacent to cylinders 3 and 4. On 2.7L, 2.8L and 4.2L engines KS I is located on right cylinder bank and monitors bank 1 cylinders. KS II is located on left cylinder bank and monitors bank 2 cylinders.
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, ECM 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.