GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2001 🢒 GMC C Sierra - 2WD 🢒 Engine 🢒 Engine Controls - 8.1L 🢒 Detonation/Spark Knock

Checks

Action

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

Preliminary Checks
    • Refer to Important Preliminary Checks Before Starting in Symptoms - Engine Controls .
    • Search for bulletins.
    • Check the PCM grounds for being clean, tight, and in the proper locations. Refer to Engine Controls Schematics .
    • If the scan tool readings are normal refer to supporting text of the Engine Controls Diagnostic Check and there are no engine mechanical faults, fill the fuel tank with a known high quality fuel that meets the vehicles minimum octane requirements. Refer to Fuel System Specifications . Road test the vehicle and re-evaluate the vehicles performance.

Fuel System
    • Check for incorrect fuel pressure. Refer to Fuel System Diagnosis .
    • Check for a restricted fuel filter. Refer to Fuel System Diagnosis .
    •  Check for a contaminated fuel condition. Refer to Alcohol/Contaminants-in-Fuel Diagnosis .
    • Check the items that can cause an engine to run lean long term fuel trim near 24 percent. For a lean condition, refer to DTC P0171 or P0174 .

Ignition System

Check the spark plugs for being the proper heat range. Refer to Spark Plug Inspection .

Engine Cooling System

Check 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

Check the engine for the following mechanical conditions:

    • Excessive oil in combustion chamber--Leaking valve seals. Refer to Oil Consumption Diagnosis in Engine Mechanical 8.1L.
    • Low cylinder compression--Refer to Engine Compression Test Engine Mechanical 8.1L.
    • Combustion chambers for excessive carbon buildup--Clean the combustion chamber by using top engine cleaner. Follow the instructions on the can.
    • Inspect the following components for incorrect basic engine parts:
       - Camshaft
       - Cylinder heads
       - Pistons, etc.
    • Refer to the appropriate procedures in Engine Mechanical 8.1L.

Additional Checks
    • Check the park/neutral position (PNP) switch operation.
    • Check the transmission torque converter clutch (TCC) operation. The TCC applying too soon can cause the engine to spark knock. Refer to Powertrain On Board Diagnostic (OBD) System Check - Automatic Transmission in Automatic Transmission-4L80E or Diagnostic System Check - Automatic Transmission in Automatic Transmission-Allison.