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.

• High Octane: This is the High Octane spark advance versus RPM and Cylinder Airmass.
• Low Octane: This is the Low Octane spark advance versus RPM and Cylinder Airmass.

  
  

• High Octane vs. MAP vs. RPM: This is the High Octane spark advance versus MAP and RPM (some I4/5/6 vehicles).
• Low Octane vs. MAP vs. RPM: This is the Low Octane spark advance versus MAP and RPM (some I4/5/6 vehicles).
• High Octane vs. MAP vs. RPM (Alcohol): This is the High Octane spark advance versus MAP and RPM when running alcohol fuel (some I4/5/6 vehicles).
• Low Octane vs. MAP vs. RPM (Alcohol): This is the Low Octane spark advance versus MAP and RPM when running alcohol fuel (some I4/5/6 vehicles).

  
  

• High Octane PE Spark vs. MAP vs. RPM: This is the High Octane spark advance used during PE mode versus MAP and RPM (some I4/5/6 vehicles).
• Low Octane PE Spark vs. MAP vs. RPM: This is the Low Octane spark advance used during PE mode versus MAP and RPM (some I4/5/6 vehicles).
• High Octane PE Spark vs. MAP vs. RPM (Alcohol): This is the High Octane spark advance used during PE mode versus MAP and RPM when running alcohol fuel (some I4/5/6 vehicles).
• Low Octane PE Spark vs. MAP vs. RPM (Alcohol): This is the Low Octane spark advance used during PE mode versus MAP and RPM when running alcohol fuel (some I4/5/6 vehicles).

  
  

• Main Spark - Intake Min, Exhaust Min: Main Spark when intake camshaft is at minimum and exhaust camshaft is at minimum.
• Main Spark - Intake Min, Exhaust Max: Main Spark when intake camshaft is at minimum and exhaust camshaft is at maximum.
• Main Spark - Intake Max, Exhaust Min: Main Spark when intake camshaft is at maximum and exhaust camshaft is at minimum.
• Main Spark - Intake Max, Exhaust Max: Main Spark when intake camshaft is at maximum and exhaust camshaft is at maximum.

  
  

• Cranking Spark: This table is used to define the spark during engine cranking.

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.

• TPS: This value is the Throttle Position required to disable the Main Spark tables
• TPS Hysteresis: This value is added to the value above as the threshold to activate Main Spark table in relation to TPS.
• Speed: This value is the Speed required to disable the Main Spark tables
• Speed Hysteresis: This value is added to the value above as the threshold to activate Main Spark table in relation to speed.

Base Spark Tables

• Base Spark vs. Airflow vs. RPM Closed Throttle, In Drive: This is the base spark used predominantly at idle with selector in gear.
• Base Spark vs. Airflow vs. RPM Closed Throttle, In Park: This is the base spark used predominantly at idle with selector in Park or Neutral.

Idle Spark Advance

• Base: This is the base spark used predominantly at idle.
• Coastdown: This is the base spark used predominantly while the vehicle in in coastdown.
• Idle Spark Adder (P/N): This adds to the current idle spark while in Park/Neutral.
• Idle Spark Adder (In Gear): This adds to the current idle spark while in Gear.
• Idle Spark Mult vs. Baro: This modifies the idle spark in relation to barometic pressure.

  
  

• Base vs. MAP: This is the base spark used predominantly at idle (some I4/5/6 vehicles).
• Base vs. MAP (Alcohol): This is the base spark used predominantly at idle when running alcohol fuel (some I4/5/6 vehicles).

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

• AFR Spark Advance Correction - Add: This table is used to modify spark advance based on the current commanded AFR value (Fuel/Air multiplier). It is used during lean cruise mode and adds to the current spark advance.
• AFR Spark Advance Correction - Mult: The multiplier table is used to proportionally enable or disable this feature in relation to MAP.
• AFR Spark Advance Correction - Gas: These values are added to the spark advance in relation to EQ Ratio. It is used in the various enrichments modes (PE, COT, etc.)
• AFR Spark Advance Correction - Alcohol: These values are added to the spark advance in relation to EQ Ratio. It is used in the various enrichments modes (PE, COT, etc.)
• AFR Spark Advance Mult vs. Fuel Composition: The multiplier table is used to modify the spark value based on fuel composition (flex fuel only).
• AFR Spark Advance Correction Mult vs. MAP: The multiplier table is used to proportionally enable or disable this feature in relation to MAP.

  
  

• IAT Spark Advance Correction - Add (Base): This table is used to modify spark advance based on inlet air temperature. It adds to the current spark advance.
• IAT Spark Advance Correction - Mult: The multiplier is used to proportionally enable or disable this feature.
• IAT Spark Advance Correction - Mult 2: The multiplier is used to proportionally enable or disable this feature.

  
  

• ECT Spark Advance Correction - Add (Base): This table is used to modify spark advance based on engine coolant temperature. It adds to the current spark advance.
• ECT Spark Advance Correction - Mult: The multiplier is used to proportionally enable or disable this feature.

  
  

• Lightoff Spark (Normal): Catalytic converter lightoff (warmup) spark table. Used to modify timing during startup to heat the cats faster.
• Lightoff Spark (Coast): Catalytic converter lightoff (warmup) spark table. Used to modify timing during startup to heat the cats faster during coastdown.
• Lightoff Spark Idle (P/N): Catalytic converter lightoff (warmup) spark table. Used to modify timing during startup to heat the cats faster during idle in Park/Neutral.
• Lightoff Spark Idle (Gear): Catalytic converter lightoff (warmup) spark table. Used to modify timing during startup to heat the cats faster during idle in Gear.

  
  

• Launch Spark: Base launch spark table. Used to modify timing during cold start takeoffs.

  
  

• Piston Slap Spark: This table is used to modify spark advance to reduce piston slap (noise) during warmup.

  
  

• Startup Spark Correction: During the first 80 seconds of engine operation the VCM has the ability to modify the spark advance based on cylinder air and time. Generally this is used to assist in cold start low speed drivability. This value adds to the spark advance.
• Startup Spark Correction Mult vs. Startup ECT: The Multiplier table is used to enable and disable startup spark correction based on coolant temperature it is a proportional value between 0 and 1.

  
  

• EGR Spark Advance Correction - Add: This table is used to modify spark advance based on EGR operating conditions. It adds to the current spark advance.

  
  

• Startup Flare Control: This table is used to adjust timing to attempt to control RPM flaring during startup.
• Startup Flare Control - Mult: The multiplier table is used to proportionally enable or disable this feature in relation to ECT.

  
  

Idle Adaptive Spark Control

• Overspeed: Amount of spark adjustment in response to an idle overspeed condition.
• Underspeed: Amount of spark adjustment in response to an idle underspeed condition.

  
  

• Overspeed (P/N): Amount of spark adjustment in response to an idle overspeed condition in Park/Neutral.
• Overspeed (Gear): Amount of spark adjustment in response to an idle overspeed condition in Gear.
• Overspeed (Coast): Amount of spark adjustment in response to an idle overspeed condition in coastdown.
• Underspeed (P/N): Amount of spark adjustment in response to an idle underspeed condition in Park/Neutral.
• Underspeed (Gear): Amount of spark adjustment in response to an idle underspeed condition in Gear.
• Underspeed (Coast): Amount of spark adjustment in response to an idle underspeed condition in coastdown.

Mean Best Timing

• Max Torque Timing vs. RPM vs. Cyl Air: Theoretical spark advance that delivers maximum torque. PCM torque calculation routines reference this table when estimating current engine torque output relative to theoretical maximum. We do not recommend modifying this table.

AC Torque Spark

• AC Bump Torque Spark: Enables/Disables spark adjustment when AC cycle on/off.
• AC Bump Torque Idle Spark: Enables/Disables spark adjustment when AC cycle on/off at idle if AC Bump Torque Spark is enabled.

M6 Spark Smoothing

• M6 Spark Smoothing: Enables/Disables spark adjustment/smoothing for M6 transmission.

V6 Spark Limiter (V6 only)

• High RPM Threshold: Above this RPM the VCM will set the spark to the value specified by High RPM Spark.
• High RPM Spark: The VCM will set the spark to this value when the RPM exceeds High RPM Threshold.
• Spark Limiter Speed vs. Gear: The VCM will retard the spark above the specified speed as a form of limiter function.