Detonation/Spark Knock/Pings

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.
^ If scan tool readings are normal (refer to Diagnostic System Check) and there are no engine mechanical faults, fill fuel tank with a premium gasoline that has a minimum octane rating of 92 and revaluate vehicle performance.
^ Check for Service Bulletin updates.
^ For correct EPROM.

COOLING SYSTEM
Check for obvious overheating problems:
- Low engine coolant.
- Loose serpentine belt.
- Restricted air flow to radiator, or restricted coolant flow.
- Inoperative electric cooling fan circuit, use CHART C-12. Chart C-12 Coolant Fan Functional Check
- Correct coolant solution should be a 50/50 mix of GM #1052753 anti-freeze coolant (or equivalent) and water.

IGNITION SYSTEM CHECKS
^ Knock Sensor (KS) system for no retard, use Chart-C5. Chart C-5 Knock Sensor (KS) System Check

ENGINE MECHANICAL CHECKS
^ For excessive oil in the combustion chamber.
- Valve oil seals for leaking.

^ Combustion chambers for excessive carbon buildup. Remove carbon with top engine cleaner and follow instructions on can.
^ Combustion chamber pressure by performing a compression test.
^ For incorrect basic engine parts such as cam, heads, pistons, etc.
^ Spark plugs for correct heat range and proper torque.

FUEL SYSTEM
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 Long Term (L.T.) fuel trim will help identify a problem.
Lean - L.T. Fuel Trim near 198. Refer to "Diagnostic Aids" in the text of Diagnostic Chart 44. Powertrain Controls - ECM/PCM
Rich - L.T. Fuel Trim near 58. Refer to "Diagnostic Aids" in the text of Diagnostic Chart 45. Powertrain Controls - ECM/PCM

^ Check fuel pressure, use CHART A-7. Related Tests, Information and Procedures

ADDITIONAL CHECKS
^ Exhaust Gas Recirculation (EGR) system, refer to CHART C-7. Chart C-7 Exhaust Gas Recirculation (EGR) System Check
^ Torque Converter Clutch (TCC) operation. TCC applying too soon. Refer to Chart C-8. Chart C-8 Torque Converter Clutch (TCC) Diagnosis
^ For intake valve deposits.