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 visual and physical checks as described under Preliminary Checks.
^ Park/Neutral Position (PNP) switch. Be sure Tech 1 scanner indicates drive with gear selector in drive or overdrive. Refer to Chart C-1A P/N Position (PNP) Switch Diagnosis.
^ If Tech 1 scanner readings are normal (refer to Scan-Tool Diagnostics / Typical Scan Data Values) and there are no engine mechanical faults, fill fuel tank with a premium gasoline that has a minimum octane reading of 92 and re-evaluate vehicle performance.

Check: Exhaust Gas Recirculation (EGR) system for not opening. Refer to Chart C-7 EGR System Check.

Check: Torque Converter Clutch (TCC) operation for TCC applying too soon. Refer to Torque Converter Clutch System.

COOLING SYSTEM
Check for obvious overheating problems:
- Low engine coolant.
- Restricted air flow to radiator, or restricted water flow through radiator.
- Inoperative electric cooling fan circuit. Refer to Chart C-12 Electric Cooling Fan Control Circuit.
- Correct coolant solution should be a 50/50 mix of GM # 1052753 or equivalent anti-freeze coolant and water.

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 fuel trim will help identify a problem.

Lean Condition
A lean condition is present when the long term fuel trim value reads near 160. Refer to "Diagnostic Aids" located in DTCs 44 and 64.

Rich Condition
A rich condition is present when the long term fuel trim value reads near 108. Refer to "Diagnostic Aids" located in DTCs 45 and 65.

Check: Fuel pressure. Refer to Chart A-7 Fuel System Diagnosis.

IGNITION SYSTEM
Check: Spark plugs for proper heat range.

Check: Knock Sensor (KS) system for no retard. Refer to Chart C-5 Knock Sensor System Check.

Check: Distributor vent system. Refer to Chart C-4C Distributor Vent System Check.

ENGINE MECHANICAL
Check: For excessive oil in the combustion chamber.
- Valve oil seals for leaking.

Check: Combustion chambers for excessive carbon buildup. Remove carbon with top engine cleaner following instructions on can.

Check: Perform a cylinder compression test.

Check: For incorrect basic engine parts such as cam, heads, pistons, etc.

ADDITIONAL CHECKS
Check: PROM Calibration I.D. for most current and/or incorrect software. Refer to PROM - Programmable Read Only Memory for calibration information.