Detonation/Spark Knock

WARNING: This page is about a different car, the 2004 GMC Sierra, 2004 GMC Cab & Chassis Sierra, 2004 Chevrolet Silverado, and 2004 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.

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 Starting in Symptoms - Engine Controls . Search for bulletins. Verify that the powertrain control module (PCM) grounds are clean, tight, and in the proper locations. Refer to Power and Grounding Component Views in Wiring Systems 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 vehicles performance.
Fuel System	Inspect for incorrect fuel pressure. Refer to Fuel System Diagnosis . Inspect for a contaminated fuel condition. Refer to Alcohol/Contaminants-in-Fuel Diagnosis (Without Special Tool) or Alcohol/Contaminants-in-Fuel Diagnosis (With Special Tool) . Inspect for the following conditions that may cause the engine to run lean: NOTE: Refer to Heated Oxygen and Oxygen Sensor Notice in Cautions and Notices. Water intrusion in the HO2S connector An exhaust leak between the HO2S and the engine-Refer to Exhaust Leakage in Engine Exhaust. Vacuum leaks Incorrect fuel pressure-Refer to Fuel System Diagnosis . Restricted fuel injectors-Refer to Fuel System Diagnosis . An inaccurate MAF sensor-Refer to Scan Tool Data List Fuel contamination-Refer to Alcohol/Contaminants-in-Fuel Diagnosis (Without Special Tool) or Alcohol/Contaminants-in-Fuel Diagnosis (With Special Tool) . Vacuum hoses that are split, kinked, or improperly connected
Ignition System	Verify that the spark plugs are of the proper heat range. Refer to Spark Plug Inspection .
Engine Cooling System	Inspect for obvious overheating problems: Low engine coolant-Refer to Loss of Coolant in Engine Cooling for the type and amount of engine coolant to be used. Restricted air flow to the radiator or restricted coolant flow through the radiator. Inoperative cooling fan - Refer to Fan Clutch Diagnosis in Engine Cooling.
Engine Mechanical	Inspect for the following engine mechanical problems: Excessive oil in combustion chamber-Leaking valve seals. Refer to Oil Consumption Diagnosis in Engine Mechanical. Low cylinder compression-Refer to Engine Compression Test Engine Mechanical. Combustion chambers for excessive carbon buildup-Clean the combustion chamber by using top engine cleaner. Follow the instructions on the can. Inspect for incorrect basic engine parts. Inspect the following: The camshaft-Refer to Camshaft and Bearings Cleaning and Inspection in Engine Mechanical. The cylinder heads-Refer to Cylinder Head Cleaning and Inspection in Engine Mechanical. The pistons, etc.-Refer to Piston, Connecting Rod, and Bearings Cleaning and Inspection in Engine Mechanical. Refer to Symptoms - Engine Mechanical in Engine Mechanical.
Additional Inspections	Inspect the park/neutral position (PNP) switch operation. Refer to Diagnostic System Check - Automatic Transmission in Automatic Transmission-4L60-E/4L65-E and Allison Transmission. Inspect the transmission torque converter clutch (TCC) operation. The TCC applying too soon can cause the engine to spark knock. Refer to Diagnostic System Check - Automatic Transmission in Automatic Transmission 4L60-E/4L65-E and Allison Transmision.