With Manual Transmission

KNOCK CONTROL





Knock is caused by auto-ignition of the air/fuel mixture in the combustion chamber. This can occur before or after the spark plug has fired. In either case, the mixture is ignited at two or more points in the combustion chamber.

This results in an extremely rapid combustion process, characterized by several flame fronts. Pressure increases rapidly and a metallic knocking noise is heard.

Knock in a cylinder produces a certain type of vibration in the block. The mechanical stresses caused to the piezoelectric crystal in the knock sensor (KS) causes the device to generate a voltage. This signal, with the signals from the camshaft position (CMP) and engine speed (RPM) sensors, is used by the engine control module (ECM) to identify which cylinder is knocking.

The knock sensors (KS) also detect some normal engine noise. Filtering, amplifying and processing the signal allows the engine control module (ECM) to recognize vibrations corresponding to engine knock.

If the knock sensors detect engine knock above a certain threshold, ignition is retarded and the fuel/air mixture is enriched in order to eliminate it.