GM Service Manual Online
For 1990-2009 cars only

Inspections

Action

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

Preliminary

    â€¢ Refer to Symptoms - Engine Controls .
    â€¢ Verify the customer's concern.

Cooling System

    â€¢ Inspect for a low engine coolant level.
    â€¢ Inspect for a correct coolant mixture.
    â€¢ Inspect for the proper tension on the drive belts. Refer to Drive Belt Tensioner Diagnosis .
    â€¢ Inspect for restricted air flow through the radiator, or restricted coolant flow.
    â€¢ Inspect for a faulty thermostat. Refer to Thermostat Diagnosis .

Sensor/System

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

Fuel System

    â€¢ Drive the vehicle at the speed of the complaint. Monitoring the fuel trim will help identify the problem.
    â€¢ If the system is lean, the long term fuel trim will be more than 150.
    â€¢ Test the fuel pressure. Refer to Fuel System Diagnosis .
    â€¢ Inspect for a poor fuel quality and a proper octane rating.
    â€¢ 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

    â€¢ Inspect the spark plugs for their proper heat range and gap.
    â€¢ Inspect the knock sensor (KS) system operation.
    â€¢ Inspect the ignition timing.

Engine Mechanical

    â€¢ Inspect for carbon build up. Remove the carbon with a top engine cleaner. Follow the instructions on the can.
    â€¢ Test the combustion chamber pressure by performing a compression test. Refer to Engine Compression Test .

Additional

    â€¢ Inspect the torque converter clutch (TCC) operation. Refer to Torque Converter Diagnosis .
    â€¢ Search for Service Bulletins for calibration updates.