GM
> Engine > Spark Control > Spark Retard
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.
- Min MAP: Minimum MAP to enable knock learn.
- Max RPM: Maximum RPM to enable knock learn.
- Min RPM: Minimum RPM to enable knock learn.
- Min ECT: Minimum ECT to enable knock learn.
- Min IAT: Minimum IAT to enable knock learn.
- Total Knock Retard: Maximum knock retard to enable knock
learn.
- Enable Multiplier vs. ECT: Proportionally enable or
disable this feature in relation to ECT.
Knock Retard Recovery Rate (Decay)
- Knock Retard Decay vs RPM High CylAir: Knock Retard
Decay Rate when CylAir exceeds threshold (below). Used on V6
engines.
- Knock Retard Decay vs RPM Low CylAir: Knock Retard Decay
Rate when CylAir is below threshold (below). Used on V6
engines.
- Cyl Air Threshold: CylAir threshold to determine which
decay rate to use. Used on V6 engines.
Knock Retard Fast Attack
- Knock Fast Attack Gain vs. Coolant Temp: This is the
gain in relation to coolant temperature.
- Knock Fast Attack Gain vs. Baro: This is the gain in
relation to barometric pressure.
- Knock Fast Attack Base Retard vs. RPM: This is the
amount of timing that is subtracted in proportion to each knock
detected. It is multiplied by the Temperature and Baro gain
factors. The higher this number is the more aggressive Knock Retard
will be.
- Knock Fast Attack Recovery Rate vs. RPM: This is the
rate at which knock retard is removed in the absence of further
knock. The higher this value is the faster knock retard will be
removed.
Burst Knock Retard
- Burst Knock Enable Delta Cyl Air Threshold vs. RPM: If
this value is exceeded the VCM will remove the amount of timing
specified in the Burst KR vs RPM table (Note: for 97/98 LS1 this
table is a single value).
- Burst Knock Retard vs. RPM: Amount of Knock Retard when
the CylAir delta threshold is exceeded.
- Burst Knock Retard vs. ECT: Amount of Knock Retard when
the CylAir delta threshold is exceeded (97/98 LS1 Only)
- Burst Knock Retard Multiplier vs. RPM: After the value
from the Burst knock Retard vs. Run Time vs. Coolant Temp table is
selected, this table provides the gain to that value based on
engine RPM. Multiplier range is 0 through 8. The Burst knock Retard
vs. Run Time vs. Coolant Temp and Burst Knock Retard Multiplier vs.
RPM tables replace the Burst Knock Retard vs. RPM table in earlier
calibrations.
- Burst knock Retard vs. Run Time vs. Coolant Temp: Base
amount of Knock Retard/Advance when the CylAir delta threshold is
exceeded. Table spark value can be from -25 to +55 degrees spark.
During the first 120 seconds of engine run time, the values in the
0 through 120 seconds rows can be in use. After 120 seconds, the
values in the 120 second row only are used. Depending on engine
temperature, the spark change can be + or -. The Burst knock Retard
vs. Run Time vs. Coolant Temp and Burst Knock Retard Multiplier vs.
RPM tables replace the Burst Knock Retard vs. RPM table in earlier
calibrations.
- Burst Knock Retard vs. CylAir Delta: Amount of Burst
Knock Retard in relation to the detected change in cylinder
airmass.
Maximum Knock Retard
- Maximum Knock Retard vs. MAP (Not in Power Enrich): This
is the maximum amount of Knock Retard when not in PE Mode.
- Maximum Knock Retard vs. RPM (in Power Enrich): This is
the maximum amount of Knock Retard when in PE Mode.
- Maximum Knock Retard vs. RPM: This is the maximum amount
of Knock Retard allowed.
- Maximum Knock Retard vs. AFR: Used on V6 engines, this
is the maximum amount of Knock Retard versus current commanded
AFR.
- Load Dynamic Knock Retard Max: Maximum allowed Knock
Retard based on load dynamics.
Minimum Spark Advance
- Minimum Spark Advance vs. RPM: This is the minimum limit
for spark advance during any retard event. Spark will not be
retarded below this value.
Static Spark Retard
- Static Spark Retard vs. RPM vs. Cylinder: Static spark
retard per cylinder.
- Static Spark Retard Enable Cylair: Cylair must be above
this to enable static spark retard per cylinder.