GM Service Manual Online
For 1990-2009 cars only

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

Preliminary Checks

Refer to Symptoms - Engine Controls .

Verify the customer concern.

Cooling System Checks

    • Check for a low engine coolant level.
    • Check for the proper tension on the drive belts.
    • Check for restricted air flow through the radiator, or for restricted coolant flow.
    • Check for a faulty thermostat. Refer to Thermostat Diagnosis in Engine Cooling.
    • Check for a correct coolant mixture.

Sensor Check

Check for an engine coolant temperature (ECT) sensor that has a shift in value. Refer to Temperature Versus Resistance .

Fuel System Checks

    • Check if a lean system causes this condition. Drive the vehicle at the speed that caused this condition. Monitoring the fuel trim will help to identify the problem.
    • If the system is lean, the long term fuel trim will be more than 150.
    • Check the fuel pressure. Refer to Fuel System Diagnosis .
    • Check for a poor fuel quality and for an incorrect octane rating.
    • If the fuel trim readings are normal and there are no engine mechanical concerns, then fill the fuel tank with a known good fuel, and re-evaluate the vehicle performance.

Ignition System Checks

    • Check the spark plugs for their proper heat range and gap.
    • Check the knock sensor (KS) system operation.
    • Check the ignition timing.

Engine Mechanical Checks

    • Check for carbon build-up. Remove the carbon with a high quality engine cleaner. Follow the instructions on the can.
    • Check the combustion chamber pressure by performing a compression test.

Additional Checks

    • Check for the proper operation of the exhaust gas recirculation (EGR) valve.
    • Check the torque converter clutch (TCC) operation. Refer to Diagnostic Starting Point - Automatic Transmission in Automatic Transmission.
    • Check the Service Bulletins for calibration updates.