Technical Description: Compensation: Knocking

Fig 1: Identifying Basic Quantity, Fuel (Knocking)

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Fig 2: Identifying Basic Quantity, Fuel (Knocking) Graph

Courtesy of SAAB-SCANIA OF AMERICA, INC.

If the engine is knocking, it is corrected by retarding the ignition for the cylinder in question. If knocking persists despite the retardation, the correction factor will be increased. Closed loop will then be deactivated (if it was active) as it would otherwise counter-compensate.

NOTE: Knock control on modern engines is not a safety function but a normal function. Consequently, it is considered normal when knock control reduces engine torque in certain cases. The engine knock control increases for e.g. high intake air temperatures or high coolant temperatures. Further influencing factors are driving at high altitudes and low octane fuel.
Certain engine variants require petrol with an octane rating of 98 RON in order to provide the specified engine torque/power.