Knock Detection Control

The KNK (knock) input signal is critical in the prevention of engine detonation. The ECM uses the knock sensor(s) to determine when, and to what degree, engine detonation is occurring and then retards ignition timing as needed. The spark advance program is designed to provide the maximum spark advance possible, while keeping the engine from producing an audible "ping". If problems occur with this input signal, detonation may result, producing significant levels of HC and NOx emissions.

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The ECM is designed to filter out KNK signal voltages that it considers are outside of the engine detonation range. Thus, a check of a knock control system by tapping on the engine close to the knock sensor may produce an output signal, but will not cause spark timing to retard. A check of the KNK signal pattern using the Diagnostic Tester Oscilloscope or lab scope may provide you the most diagnostic information.

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