GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Buick 🢒 1999 🢒 Century (China) (CNG) 🢒 Engine 🢒 Engine Controls - 3.0L (L46) 🢒 Detonation/Spark Knock

Detonation/Spark Knock

Checks

Action

DEFINTION: A mild to severe Ping, usually worse under acceleration. The engine makes sharp metallic knocks that change with throttle opening.

Preliminary Checks
    •  Refer to Intermittent Conditions Before Starting.
    •  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 Diagnosis .
    •  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 Spark Plug Usage .

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 antifreeze coolant and water. Refer to Fluid and Lubricant Recommendations .

Engine Mechanical
    • Excessive oil in combustion chamber--Leaking valve seals. Refer to Oil Consumption Diagnosis .
    •  Low cylinder compression. Refer to Engine Compression Test .
    •  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 P1404 Exhaust Gas Recirculation (EGR) Closed Position Performance .
    •  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 Functional Test .
    •  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.