Knock Control: Function

WARNING: This page does not describe the selected car, but rather 10 other vehicles, including the 2004 Land Rover Discovery, 2003 Land Rover Discovery, 2002 Land Rover Range Rover, 2002 Land Rover Discovery, and 2001 Land Rover Range Rover. However, it is still accessible from the selected car via links, so may be relevant.

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.