GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2003 🢒 GMC MD Steel Tilt (W Model) 🢒 Engine 🢒 Engine Controls - 4.8L, 5.3L, and 6.0L 🢒 Detonation/Spark Knock

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 Starting in Symptoms - Engine Controls .
    • Search for bulletins.
    • Verify that the powertrain control module (PCM) grounds are clean, tight, and in the proper locations.
    • 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 restricted fuel filter. Refer to Fuel System Diagnosis .
    • Inspect for a contaminated fuel condition. Refer to Alcohol/Contaminants-in-Fuel Diagnosis .
    • Inspect for the following conditions that may cause the engine to run lean:

Notice: Refer to Heated Oxygen and Oxygen Sensor Notice in the Preface section.

       - Water intrusion in the HO2S connector
       - An exhaust leak between the HO2S and the engine.
       - Vacuum leaks
       - Incorrect fuel pressure--Refer to Fuel System Diagnosis .
       - Restricted fuel injectors--Refer to Fuel System Diagnosis .
       - An inaccurate MAF sensor
       - Fuel contamination--Refer to Alcohol/Contaminants-in-Fuel Diagnosis .
       - 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.
    • Restricted air flow to the radiator or restricted coolant flow through the radiator.
    • Inoperative cooling fan.

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 Bearing Cleaning and Inspection in Engine Mechanical.
    • Refer to Symptoms - Engine Mechanical in Engine Mechanical.

Additional Inspections
    • Inspect the park/neutral position (PNP) switch operation.
    • Inspect the transmission torque converter clutch (TCC) operation. The TCC applying too soon can cause the engine to spark knock.