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." Testing and Inspection
^ Make sure the customer has an actual problem.
^ Check fuel quality. Refer to "Specific Gravity Check."

FUEL SYSTEM
^ CHECK: For air leaks in fuel supply to injection pump. Refer to Fuel System Diagnosis.
^ CHECK: Injection pump static timing.
^ CHECK: Injection nozzles.

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 degrees 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 "DTC 15" and compare resistance values. Powertrain Controls - ECM/PCM

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.