GM Service Manual Online
For 1990-2009 cars only

Detonation/Spark Knock

Checks

Action

DEFINITION: A mild to severe ping, usually worse under acceleration. The engine makes sharp metallic knocks that change with throttle opening.

Preliminary Checks

    • Refer to Important Preliminary Checks Before Starting in Symptoms - Engine Controls .
    • Search for bulletins.
    • Check the powertrain control module (PCM) grounds for being clean, tight, and in the proper locations. Refer to Engine Controls Schematics .
    • If the scan tool readings are normal refer to supporting text of the Diagnostic System Check--Engine Controls and there are no engine mechanical faults, fill the fuel tank with a known high quality fuel that meets the vehicles minimum octane requirements. Refer to Fuel System Specifications . Road test the vehicle and re-evaluate the vehicles performance.

Fuel System

    • Check for incorrect fuel pressure. Refer to Fuel System Diagnosis .
    • Check for a restricted fuel filter. Refer to Fuel System Diagnosis .
    •  Check for a contaminated fuel condition. Refer to Alcohol/Contaminants-in-Fuel Diagnosis .
    • Check the items that can cause an engine to run lean long term fuel trim near 24 percent. For a lean condition, refer to DTC P0131 or P0151 .

Ignition System

Check the spark plugs for being the proper heat range. Refer to Spark Plug Inspection in Engine Electrical.

Engine Cooling System

Check for obvious overheating problems:

    • Low engine coolant--Refer to Loss of Coolant in Engine Cooling for the type and amount of engine coolant to be used.
    • Restricted air flow to the radiator or restricted coolant flow through the radiator.
    • Inoperative cooling fan--Refer to Fan Clutch Diagnosis in Engine Cooling.

Engine Mechanical

Check for the following engine mechanical problems:

    • Excessive oil in combustion chamber--Leaking valve seals. Refer to Oil Consumption Diagnosis in Engine Mechanical 4.8L, 5.3L, 6.0L.
    • Low cylinder compression--Refer to Engine Compression Test Engine Mechanical 4.8L, 5.3L, 6.0L.
    • Combustion chambers for excessive carbon buildup--Clean the combustion chamber by using top engine cleaner. Follow the instructions on the can.
    • Check for incorrect basic engine parts. Inspect the following:
       - Camshaft
       - Cylinder heads
       - Pistons, etc.

Additional Checks

    • Check the park/neutral position (PNP) switch operation. Refer to Park/Neutral Position Switch Adjustment in Automatic Transmission-4L60-E.
    • Check the transmission torque converter clutch (TCC) operation. The TCC applying too soon can cause the engine to spark knock. Refer to Diagnostic Starting Point - Automatic Transmission in Automatic Transmission 4L60E or Diagnostic Starting Point - Automatic Transmission in Automatic Transmission 4L80E.