Fuel Knock/Combustion Noise

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.
- Make sure the customer has an actual problem.
- Check fuel quality. Refer to Specific Gravity Check in Fuel Delivery.

FUEL SYSTEM
- CHECK: For air leaks in fuel supply to injection pump. Refer to Fuel System Diagnosis in Fuel Delivery. Testing and Inspection
- CHECK: Injection pump static timing Refer to Fuel Delivery. Adjustments
- CHECK: Injection nozzles. Refer to Fuel Delivery. Testing and Inspection

SENSOR
- CHECK: Engine Coolant Temperature (ECT) sensor - Using a scan tool, compare engine coolant temperature with ambient temperature on a cold engine.
- If coolant temperature reading is 5° greater than or less than ambient air temperature on a cold engine, check for high resistance in coolant sensor circuit or sensor itself. Refer to Diagnostic Trouble Code (DTC) 15/DTC Charts and compare resistance values. Testing and Inspection

ENGINE MECHANICAL
- CHECK: For incorrect basic engine parts such as cam, heads, pistons, etc.
- CHECK: For excessive oil entering combustion chamber.

ADDITIONAL CHECKS
- CHECK: Service Bulletins for PROM updates. Refer to Programmable Read Only Memory (PROM). PROM - Programmable Read Only Memory