GM > Engine > Spark Control > Spark Advance


Main Spark Tables
The VCM constantly looks up both High Octane and Low Octane spark tables and interpolates a value between the two tables based on the current Knock Learn factor. If the engine has been operating for a moderate time without any Knock Retard then Knock Learn is zero and the interpolation favors the High Octane table, if Knock has been detected then the interpolation will move towards the Low Octane table. During MAF failure the Knock Learn is set to maximum and the Low Octane table is used (HP Tuners speed density enhancements allow both spark tables to function).


Note: Excessive spark advance will cause knock (detonation, pinging) and lead to severe engine damage. Do NOT rely on knock sensors as the only source of detecting knock during tuning.



Main Spark Table Selects
If either of these TPS or MPH values is exceeded the VCM will select the Main Spark tables, otherwise the Base Spark tables are used. The value minus the hysteresis is required to revert back to the Base table from the Main tables.


Base Spark Tables


Idle Spark Advance


Spark Correction
The VCM incorporates a number of corrections to the spark advance depending on current engine operating conditions.


Idle Adaptive Spark Control


Mean Best Timing


AC Torque Spark


M6 Spark Smoothing


V6 Spark Limiter (V6 only)