GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2004 🢒 TopKick C-Series (Conventional) C4/C5 🢒 Engine 🢒 Engine Controls - 6.6L (LB7) 🢒 Fuel Knock/Combustion Noise

Inspection

Action

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

Preliminary Inspection
    • Refer to Symptoms - Engine Controls .
    • Ensure the vehicle has an actual problem.
    • Compare the scan tool data with the scan tool data list while the engine is idling. Refer to Scan Tool Data List .
    • Inspect for smoke associated with the combustion noise. Refer to Fuel System Inspection below.

Cooling System Inspection
    • Inspect for obvious overheating problems. Refer to Diagnostic Starting Point - Engine Cooling in Engine Cooling.
    • Inspect for a low engine coolant level.
    • Inspect for any restricted air flow through the radiator. Refer to Radiator Cleaning in Engine Cooling.
    • Inspect for a malfunctioning or incorrect thermostat.
    • Inspect for a correct coolant solution. The solution should be a 50/50 mix of anti-freeze and water.

Sensor Inspection
    • Inspect the engine coolant temperature (ECT) sensor by using the scan tool in order to compare the ECT with the ambient air temperature on a cold engine. If the coolant temperature reading is more than 5 degrees more or less than the ambient air temperature on a cold engine, inspect for a high resistance in the coolant sensor circuit or the sensor itself.
    • Inspect the fuel rail pressure (FRP) sensor. Use the scan tool to observe FRP with the engine OFF. FRP should be between 1.1-1.4 MPa. If not , inspect for high resistance in the low reference or 5-volt reference circuits, or the sensor.
    • Inspect for an intermittent crankshaft position (CKP) sensor signal. Refer to Intermittent Conditions .

Fuel System Inspection
    • If excessive smoke is present, inspect for a stuck open fuel injector by performing the following procedure:
        1. Remove the ignition 1 relay.
        2. Remove the glow plugs. Refer to Glow Plug Replacement - Bank 1 and Glow Plug Replacement - Bank 2 .

        Important: Do not stand in front of the glow plug holes while cranking the engine.

        3. Crank the engine while observing the glow plug holes for fuel spray.
        4. Replace the fuel injectors for the cylinders that spray fuel.
        5. Check for fuel in the oil and proper oil level. Refer to Fuel in Engine Oil in Engine Mechanical-6.6L.
    • Inspect for plugged fuel injectors. Refer to Fuel Injector Balance Test with Tech 2 .

Engine Mechanical Inspection

Inspect the following components for incorrect basic engine parts:

    • The camshaft--Refer to Camshaft and Bearings Cleaning and Inspection in Engine Mechanical-6.6L.
    • The cylinder heads--Refer to Cylinder Head Cleaning and Inspection in Engine Mechanical-6.6L.
    • The piston, connecting rod, or bearings--Refer to Piston, Connecting Rod, and Bearing Cleaning and Inspection in Engine Mechanical-6.6L.

Additional Inspection

Review the Service Bulletins for control module software updates.