GM Service Manual Online
For 1990-2009 cars only

Checks

Action

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

Preliminary

    â€¢ Refer to Important Preliminary Checks Before Starting in Symptoms - Engine Controls .
    â€¢ Search for bulletins.

Fuel System

    â€¢ Check the fuel pressure. Refer to Fuel System Diagnosis .
    â€¢ Check for items that cause the engine to run lean.
    â€¢ Check for contaminated fuel. Refer to Alcohol/Contaminants-in-Fuel Diagnosis .

Ignition System

Check the spark plugs. Refer to Spark Plug Inspection

Engine Cooling System

Check for causes of overheating:

    â€¢ Low engine coolant level. Refer to Oil Consumption Diagnosis in Engine Cooling.
    â€¢ Restricted air flow to radiator, or restricted coolant flow through the radiator. Refer to Engine Overheating in Engine Cooling.
    â€¢ Insufficient cooling fan operation. Refer to Cooling Fan Inoperative in Engine Cooling.

Engine Mechanical

    â€¢ Check for excessive oil in the combustion chamber-leaking valve seals.
    â€¢ Engine compression
    â€¢ Check the combustion chamber for excessive carbon buildup. Clean using Top Engine Cleaner.
    â€¢ Check for incorrect basic engine parts. Inspect the following:
       - Camshafts
       - Cylinder heads
       - Pistons, etc.

Additional Checks

    â€¢ Check the torque converter clutch (TCC) system for proper operation. Refer to Torque Converter Diagnosis in Automatic Transaxle.
    â€¢ If the scan tool readings are normal, 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.