Knock Control

Knock Control
The ECM uses active knock control to prevent possible engine damage due to pre-ignition. This is achieved by converting engine block noise into a suitable electrical signal that can be processed by the ECM. A major contributing factor to engine 'knock' is fuel quality, the ECM can function satisfactorily on 91 RON fuel as well as the 95 RON fuel that it is calibrated for.

Conditions
The ECM knock control system operates as follows:
^ Hot running engine.
^ 91 or 95 RON fuel.

Function
The ECM knock control uses two sensors located one between the centre 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.