Detonation/Spark Knock. Buick Skylark 1997

Checks

Action

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 the Powertrain On Board Diagnostic (OBD) System Check

•	Refer to Important Preliminary Checks Before Starting.

•	Refer to Visual/Physical Checks

•	Search for bulletins.

Fuel System

•	Check for low fuel pressure. Refer to Fuel System Pressure Test .

•	Check for contaminated fuel. Refer to Alcohol/Contaminants-in-Fuel Test .

•	Check items that can cause an engine to run lean (long term fuel trim significantly in the positive range). Refer to Diagnostic Aids for DTC P0171.

Ignition System

•	Check the spark plugs for proper heat range and reach. Refer to General Information.

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.

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 for proper EGR system Operation. Refer to DTC P0401 Exhaust Gas Recirculation (EGR) Flow Insufficient .

•	Check the Transaxle Range Switch input with the vehicle in drive and the gear selector in drive or overdrive.

•	Check TCC operation. TCC applying too soon can cause the engine to spark knock. Refer to Torque Converter Clutch in Transaxle Diagnosis.

•	If scan tool readings are normal and there are no engine mechanical faults, fill the fuel tank with a known quality gasoline that has a minimum octane reading of 87 and re-evaluate vehicle performance.