Spark Knock Control

The PCM uses the knock sensor to determine when spark knock exists and can retard timing up to a maximum of 15°. The knock sensor is a piezoelectric flat response (wide resonant band) device that produces an AC voltage of different amplitude and frequency based on engine mechanical vibration. The amplitude and frequency are dependent on the level of knock the sensor detects.

The PCM learns an average noise level from the knock sensor (based on a calibrated average) and monitors the signal to verify that it stays above a minimum value. The knock sensor signal is only used during the top dead center combustion event of the firing cylinder. When in a combustion event, the PCM filters the knock signal and compares it to the normal calibration noise level for that RPM. If the PCM has determined that knock is present during the combustion event, it will retard timing on the next firing cylinders until the knock is eliminated. The PCM will always try to work back to a zero compensation level or no spark retard.

The Scan tool displays the actual amount of spark advance degrees and actual amount of spark retard degrees as SPARK and SPARK RETARD CYL # 1-4. If excessive spark knock is detected, the retarding of timing will cause a reduced power condition.