GM Service Manual Online
For 1990-2009 cars only

Inspection

Action

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

Preliminary

    • Refer to Important Preliminary Inspections before starting in Symptoms - Engine Controls .
    • Inspect the engine control system grounds for being clean, tight, and in the correct locations. Refer to Engine Controls Schematics . Ensure the resistance between the engine control module (ECM) housing and the battery negative cable is less than 0.5 ohms.
    • Verify that the ECM and ECM bracket fasteners are at the correct torque.
    • If the scan tool readings are normal and there are not any engine mechanical faults, fill the fuel tank with a known high quality fuel that meets the vehicle's minimum octane requirements. Road test the vehicle and re-evaluate the vehicle's performance.

Fuel System

    • Test for incorrect fuel pressure. Refer to Fuel System Diagnosis .
    • Test for a restricted fuel filter. Refer to Fuel System Diagnosis .
    • Test for a contaminated fuel condition. Refer to Alcohol/Contaminants-in-Fuel Diagnosis .
    • Test the fuel injectors. Refer to Fuel Injector Solenoid Coil Test .
    • Test the items that can cause an engine to run lean. For a lean condition, refer to DTC P2177 or P2179 and DTC P2187 or P2189 .

Sensor/System

Use a scan tool to monitor the knock sensor (KS) system. Refer to Knock Sensor (KS) System Description .

Ignition System

Ensure that the spark plugs are the correct heat range. Refer to Ignition System Specifications .

Engine Cooling System

Test for obvious overheating conditions. Test or inspect for the following conditions:

    • Low engine coolant level
    • Incorrect engine coolant
    • Restricted air flow to the radiator or restricted coolant flow through the radiator
    • Engine coolant leaks
        Refer to the following procedures in Engine Cooling:
       -  Engine Overheating

Engine Mechanical

    • Inspect for the following engine mechanical conditions:
       - Excessive oil in combustion chambers and for leaking valve seals
       - High cylinder compression
       - Incorrect camshaft timing
       - Excessive carbon buildup in the combustion chambers--Clean the chambers using top engine cleaner. Follow the instructions on the can.
       - For more information, refer to the following procedures:
    • Inspect the following components for incorrect basic engine parts:
       - Camshafts
       - Cylinder heads
       - Pistons, connecting rods, or bearings
       - Refer to the following procedures:

Additional

Test the transmission torque converter clutch (TCC) for the correct operation. Applying the TCC too soon can cause the engine to spark knock. Refer to Torque Converter Diagnosis .