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Knock Learn
Knock Learn is a method the VCM uses to provide a longer term adjustment for fuel octane. If the VCM detects knock it will instantaneously reduce timing (Knock Retard) but will also modify the Knock Learn factor to affect the proportion the VCM uses to interpolate between the High Octane and Low Octane Main Spark tables. If no knock is detected over a reasonable period then the Knock Learn factor will slowly return to the High Octane table.

If a MAF DTC is set then the knock learn factor is set to the Low Octane tables. (HP Tuners speed density enhancements disable this behavior).

The various thresholds determine when the VCM will modify the knock learn factor. The knock learn factor can be logged using the scanner on many vehicles.

Knock Retard Recovery Rate (Decay)

Knock Retard Fast Attack

Burst Knock Retard

Maximum Knock Retard

Minimum Spark Advance

Static Spark Retard