Detonation/Spark Knock. Buick Roadmaster 1996

For 1990-2009 cars

#### Detonation/Spark Knock

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 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.

• | If 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 re-evaluate 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 Test .

• | Check items which can cause an engine to run rich (long term fuel trim near -14%). 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 22%). 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. Refer to Owners Manual or Section OB.

• | 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 Park/Neutral Position Switch Check .

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