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

^ Refer to Symptoms, Important Preliminary Checks Before Starting.

^ Search for bulletins.

^ Check PCM grounds for being clean, tight and in their proper locations. Refer to PCM wiring diagrams in Electrical Diagnosis.

^ It the scan tool readings are normal (refer to supporting text of the Powertrain On-Board Diagnostic (OBD) System Check) and there are no engine mechanical faults. Fill the fuel tank with a premium gasoline that has a minimum octane reading of 92 and reevaluate vehicle performance.

FUEL SYSTEM

^ Check for low fuel pressure. Refer to Fuel System Diagnosis.

^ Check for restricted fuel filter. Refer to Fuel System Diagnosis.

^ Check for contaminated fuel. Refer to Alcohol/Contaminants-in-Fuel Testing Procedure

^ Check items which can cause an engine to run rich (long term fuel trim near -99%). For a Rich condition, refer to DTC P0132 HO2S Circuit High Voltage Bank 1 Sensor 1 and DTC P0152 HO2S Circuit High Voltage Bank 2 Sensor 1.

^ Check items that can cause an engine to run lean (long term fuel trim near 100%). For a Lean condition, refer to DTC P0131 HO2S Circuit Low Voltage Bank 1 Sensor 1 and DTC P0151 HO2S Circuit Low Voltage Bank 2 Sensor 1.

IGNITION SYSTEM

^ Spark plugs for proper heat range.

^ Check distributor vent system for being restricted or open. Refer to Distributor Vent System Check

ENGINE 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(s). Refer to Electric Cooling Fan Diagnosis.

^ Correct coolant solution should be a 50/50 mix of GM 1052753 or equivalent antifreeze coolant and water. Refer to Engine Cooling (6B).

ENGINE MECHANICAL

^ Excessive oil in combustion chamber-Leaking valve seals. Refer to Engine Mechanical

^ Low cylinder compression. Refer to Engine Mechanical.

^ Combustion chambers for excessive carbon buildup. Clean using Top engine cleaner. Follow instructions on can.

^ For incorrect basic engine parts. Inspect the following:

- Camshaft

- Cylinder heads

- Pistons, etc.

^ Refer to Engine Mechanical.

ADDITIONAL CHECKS

^ Check Park/Neutral Position (PNP) switch operation. Connect scan tool and monitor PNP signal. The scan tool should indicate P-N- when in park or neutral and -R-OD21 when in any forward gear or reverse. Refer to PNP Switch Check

^ Check TCC operation. TCC applying too soon can cause the engine to spark knock. Refer to Transmission Controls.