Fuel Knock/Combustion Noise

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.

Checks	Action
DEFINITION: A mild to severe ping, usually worse under acceleration. The engine makes sharp metallic knocks that change with the throttle opening.
Preliminary Checks	Refer to Symptoms - Engine Controls . Ensure the vehicle has an actual problem. Inspect for smoke associated with the combustion noise. Refer to Fuel System Checks below.
Cooling System Checks	Inspect for obvious overheating problems. Refer to Engine Overheating 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, check 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 ignition ON and the engine OFF. FRP should be 1.1-1.4 MPa. If FRP is not within this range, check for high resistance in the low reference or 5-volt reference circuits or the sensor, or a faulty sensor. Inspect for an intermittent crankshaft position (CKP) sensor signal. Refer to Intermittent Conditions . Inspect the crankshaft position (CKP) sensor reluctor wheel. Remove the CKP sensor and attempt to move the reluctor wheel front to back or side to side with a probe. If there is any movement the reluctor wheel retaining bolts are loose.
Fuel System Checks	If excessive smoke is present, check for a stuck open fuel injector by performing the following procedure: Remove the ignition 1 relay. 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. Crank the engine while observing the glow plug holes for fuel spray. Replace the fuel injectors for the cylinders that spray fuel. Check for fuel in the oil and proper oil level. Refer to Fuel in Engine Oil in Engine Mechanical. Inspect for plugged fuel injectors. Refer to Fuel Injector Balance Test with Tech 2 (with Automatic Transmission) or Fuel Injector Balance Test with Tech 2 (with Manual Transmission) .
Engine Mechanical Checks	Inspect for incorrect basic engine parts such as cam, heads, pistons, etc. Inspect for any excessive oil entering combustion chamber.
Additional Checks	Review the Service Bulletins for control module software updates. Compare the scan tool data at idle with the scan tool data list. Refer to Scan Tool Data List .