Knock Control: Function

The ECM knock control uses two sensors located one between the center two cylinders of each bank. The knock sensors consist of piezo ceramic crystals that oscillate to create a voltage signal. During pre-ignition, the frequency of crystal oscillation increases which alters the signal output to the ECM.

If the knock sensors detect pre-ignition in any of the cylinders, the ECM retards the ignition timing by 3° for that particular cylinder. If this action stops the engine knock, the ignition timing is restored to its previous figure in increments of 0.75°. If this action does not stop engine knock then the ECM retards the ignition timing a further 3° up to a maximum of -15° and then restores it by 0.75° and so on until the engine knock is eliminated.

The ECM also counteracts engine knock at high intake air temperatures by retarding the ignition as above. The ECM uses the IAT signal to determine air temperature.