Fuel Knock/Combustion Noise

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 . Make sure the vehicle has an actual problem. Check the fuel quality.
Cooling System Checks	Check for obvious overheating problems. Refer to Engine Overheating in Engine Cooling. Check for a low engine coolant level. Check for a loose water pump belt. Check for any restricted air flow through the radiator, or restricted coolant flow. Check for a malfunctioning or incorrect thermostat. Check for a correct coolant solution. The solution should be a 50/50 mix of anti-freeze and water.
Sensor Check	Check the engine coolant temperature (ECT) sensor by using the scan tool in order to compare the engine coolant temperature 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.
Fuel System Checks	Check for air leaks in the fuel supply to the injection pump. Refer to Fuel System Diagnosis . Check the injection pump static timing. Refer to Fuel Injection Pump Timing Adjustment . Check the injection nozzles. Refer to Fuel Injection Nozzle Diagnosis .
Engine Mechanical Checks	Check for incorrect basic engine parts such as cam, heads, pistons, etc. Check for any excessive oil entering combustion chamber.
Additional Checks	Check the Service Bulletins for control module software updates.