Detonation/Spark Knock

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

PRELIMINARY CHECKS
^ Perform the careful visual / physical checks as described in Preliminary Checks.
^ Make sure the customer has an actual problem.
^ If an injector is suspect on Central MFI engine, refer to Procedures / Diagnostic Charts / Chart A-6 Fuel System Diagnosis. Testing and Inspection
^ Check trans Range (TR) pressure switch assembly operation. Refer to Procedures / Diagnostic Charts / C Charts / Transmission Range Pressure Switch Circuit Check. Testing and Inspection

COOLING SYSTEM
^ Check for low engine coolant and obvious overheating problems.
^ Check for a loose water pump belt.
^ Check for restricted air flow to radiator, or restricted coolant flow.
^ Check for a faulty or incorrect thermostat.
^ Correct coolant solution should be a 50/5O mix of GM #1052753 anti-freeze coolant (or equivalent) and water.

SENSOR
^ Check the Engine Coolant Temperature (ECT) sensor which has shifted in value. Refer to Procedures / Diagnostic Charts / Code 15 Coolant Sensor Circuit. Testing and Inspection

FUEL SYSTEM
^ Check to determine if the condition is caused by a rich or lean system, the vehicle should be driven at the speed of the complaint. Monitoring fuel trim will help identify problem.
Lean - Long term trim greater than 150, refer to Procedures / Diagnostic Charts / Code 44 Oxygen Sensor Circuit, "Diagnostic Aids". Testing and Inspection
^ Check the fuel pressure, refer to Procedures / Diagnostic Charts / Chart A-6 Fuel System Diagnosis. Testing and Inspection
^ Check for poor fuel quality and proper octane rating. If scan tool readings are normal and there are no engine mechanical faults, fill fuel tank with a premium gasoline that has a minimum octane rating of 92 and re-evaluate vehicle performance.

IGNITION SYSTEM
^ Check spark plugs for proper heat range and gap.
^ Check knock sensor system for proper operation, refer to Procedures / Diagnostic Charts / C Charts / Knock Sensor (KS) System. Testing and Inspection
^ Check ignition timing.

ENGINE MECHANICAL
^ Check combustion chambers for excessive carbon buildup. Remove carbon with top end engine cleaner and follow instructions on can.
^ Check for incorrect basic engine parts such as cam, heads, pistons, etc.

ADDITIONAL CHECKS
^ Check for proper operation of Exhaust Gas Recirculation (EGR) valve.
^ Check for proper operation of air intake system.
^ Check for proper transmission shift points.
^ Check the [1][2]Torque Converter Clutch (TCC) operation.
^ Check Service Bulletins for PROM updates.