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 Symptoms - Engine Controls , Important Preliminary Checks Before Starting.
    • Search for bulletins.
    • Verify that the PCM grounds are clean, tight, and in the correct locations.
    • 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 premium gasoline that has a minimum octane reading of 92 and re-evaluate the vehicle's performance.

Fuel System

    • Check for a low fuel pressure. Refer to Cuts Out, Misses .
    • Check for a restricted fuel filter.
    •  Check for contaminated fuel. Refer to Alcohol/Contaminants-in-Fuel Diagnosis .
    • Check the items that can cause an engine to run rich.
    • Check items that can cause an engine to run lean.

Ignition System

Check the spark plugs for the correct heat range.

Engine Cooling System

Check for obvious overheating problems:

    • A low engine coolant level
    • A restricted air flow to the radiator, or restricted water flow through the radiator
    • Check for any inoperative cooling fans. Refer to Electric Cooling Fan Diagnosis.
    • Refer to Engine Overheating in Engine Cooling.

Engine Mechanical

Check for the following conditions:

    • Any excessive oil in the combustion chambers may indicate leaking valve seals. Refer to Oil Consumption Diagnosis in Engine Mechanical.
    • A low cylinder compression--Refer to Engine Compression Test in Engine Mechanical.
    • Any excessive carbon buildup in the combustion chambers. Clean the chambers using Top Engine cleaner. Follow the instructions on the container.
    • Any incorrect basic engine parts--Inspect the following parts:
       - The camshaft
       - The cylinder heads
       - The pistons, etc.

Refer to Symptoms - Engine Mechanical in Engine Mechanical.

Additional Checks

    • Check for the correct transaxle range switch operation.
    • Check the toque 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 Transaxle.