GM Service Manual Online
For 1990-2009 cars only

Inspection/Test

Action

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

Preliminary

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

Fuel System

    • Test the fuel pressure. Refer to Fuel System Diagnosis .
    • Test for contaminated fuel. Refer to Alcohol/Contaminants-in-Fuel Diagnosis .

Inspect the following that may cause the engine to run lean:

Notice: Refer to Heated Oxygen and Oxygen Sensor Notice in the Preface section.

    • Any water intrusion into the HO2S connector.
    • An exhaust leak between the HO2S and the engine--Refer to Exhaust Leakage in Engine Exhaust.
    • Any vacuum leaks.
    • Incorrect fuel pressure--Refer to Fuel System Diagnosis .
    • An inaccurate mass air flow (MAF) sensor.
    • Fuel Contamination--Refer to Alcohol/Contaminants-in-Fuel Diagnosis .
    • Vacuum hoses for splits, kinks and proper connections.

Ignition System

Inspect the spark plugs. Refer to Spark Plug Inspection

Engine Cooling System

Inspect for causes of overheating:

    • Low engine coolant level. Refer to Loss of Coolant in Engine Cooling.
    • Restricted air flow to radiator, or restricted coolant flow through the radiator. Refer to Engine Overheating in Engine Cooling.
    • Insufficient cooling fan operation. Refer to Cooling Fan Inoperative in Engine Cooling.

Engine Mechanical

    • Inspect for excessive oil in the combustion chamber-leaking valve seals. Refer to Oil Consumption Diagnosis in Engine Mechanical.
    • Engine compression--Refer to Engine Compression Test in Engine Mechanical.
    • Inspect the combustion chamber for excessive carbon buildup. Clean using Top Engine Cleaner. Follow instructions on can.
    • Inspect the following for incorrect basic engine parts:
       - Camshafts
       - Cylinder heads
       - Pistons, etc.

Additional

    • Inspect the torque converter clutch (TCC) system for proper operation. Refer to Torque Converter Diagnosis in Automatic Transaxle.
    • 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.