GM Service Manual Online
For 1990-2009 cars only

Check

Action

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 .

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 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 of the complaint. Monitoring the Fuel Trim will help identify the problem.
    • If the system is Lean, the Long Term Fuel Trim will be greater than 150.
    • Check the fuel pressure. Refer to Fuel System Diagnosis .
    • Check for a poor fuel quality and a proper 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's 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 top 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 EGR Valve. Refer to Exhaust Gas Recirculation (EGR) System Diagnosis .
    • Check the Torque Converter Clutch (TCC) operation. Refer to Diagnostic Starting Point - Automatic Transmission (4L60E) or Diagnostic Starting Point - Automatic Transmission (4L80E) in Automatic Transmission.
    • Check the Service Bulletins for calibration updates.