Detonation/Spark Knock

Inspection/Tests	Action
DEFINITION: A mild to severe ping, usually worse under acceleration. The engine makes sharp metallic knocks that change with throttle opening.
Preliminary Inspections	Refer to Important Preliminary Inspections Before Beginning . Search for bulletins. Inspect the powertrain control module (PCM) grounds for being clean, tight, and in the proper locations. Refer to Power and Grounding Component Views and Engine Controls Schematics . If there are no engine mechanical faults, fill the fuel tank with a known high quality fuel that meets the vehicles minimum octane requirements. Road test the vehicle and re-evaluate the performance of the vehicle.
Fuel System	Test for incorrect fuel pressure. Refer to Fuel System Diagnosis . Inspect for a restricted fuel filter. Refer to Fuel System Diagnosis . Test the fuel injectors. Refer to Fuel Injector Diagnosis (w/J39021 or w/Tech 2) or Fuel Injector Diagnosis (w/CH47976) . Inspect for a contaminated fuel condition. Refer to Alcohol/Contaminants-in-Fuel Diagnosis (with Special Tool) or Alcohol/Contaminants-in-Fuel Diagnosis (without Special Tool) . Inspect for the following conditions that may cause the engine to run lean: NOTE: Refer to Heated Oxygen and Oxygen Sensor Notice . Water intrusion in the heated oxygen sensor (HO2S) connector An exhaust leak between the HO2S and the engine-Refer to Exhaust Leakage . Vacuum leaks Incorrect fuel pressure-Refer to Fuel System Diagnosis . Restricted fuel injectors-Refer to Fuel Injector Diagnosis (w/J39021 or w/Tech 2) or Fuel Injector Diagnosis (w/CH47976) . Inspect for proper operation of the manifold absolute pressure (MAP) sensor-Refer to Altitude Versus Barometric Pressure . Fuel contamination-Refer to Alcohol/Contaminants-in-Fuel Diagnosis (with Special Tool) or Alcohol/Contaminants-in-Fuel Diagnosis (without Special Tool) . Vacuum hoses that are split, kinked, or improperly connected
Sensor/System	Inspect for an engine coolant temperature (ECT) sensor that has shifted in value. Refer to Temperature Versus Resistance .
Ignition System	In order to properly inspect the spark plugs or to correct a condition, refer to the following procedures: Ignition System Specifications Spark Plug Replacement Spark Plug Inspection Remove spark plugs and inspect for the following: Correct heat range Wet plugs Cracks Wear Improper gap Burned electrodes Heavy deposits Verify that the spark plugs are of the correct type. Inspect for proper secondary ignition voltage output with J 26792 HEI Spark Tester. See Special Tools . An improper spark plug gap will cause a driveability condition. Gap the spark plugs using a wire gage gap tool. If the spark plugs are found to be fouled, determine the cause before replacing the spark plugs. Inspect for damaged or misaligned spark plug boots.
Engine Cooling System	Inspect for obvious overheating problems: Low engine coolant-Refer to Loss of Coolant (2.9L) or Loss of Coolant (3.7L) . Faulty thermostat. Refer to Thermostat Diagnosis . Restricted air flow to the radiator or restricted coolant flow through the radiator. Inoperative cooling fan - Refer to Fan Clutch Diagnosis . Proper tension on the drive belts. Correct coolant solution should be a 50/50 mix. Refer to Cooling System Description and Operation .
Engine Mechanical	Inspect for the following engine mechanical problems: Excessive oil in combustion chamber-Leaking valve seals. Refer to Oil Consumption Diagnosis . High cylinder compression-Refer to Engine Compression Test . Combustion chambers for excessive carbon buildup-Clean the combustion chamber by using top engine cleaner. Follow the instructions on the can. Incorrect camshaft timing Inspect for incorrect, worn, or damaged basic engine parts. Inspect the following: The camshaft-Refer to Camshafts Cleaning and Inspection . The cylinder heads-Refer to Cylinder Head Cleaning and Inspection . The pistons, etc.-Refer to Piston, Connecting Rod, and Bearings Cleaning and Inspection .
Additional Inspections	Inspect the transmission torque converter clutch (TCC) operation. Refer to Symptoms - Automatic Transmission for the 4L60-E/4L65-E transmission.