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For 1990-2009 cars only
Makes 🢒 Buick 🢒 2001 🢒 Century 🢒 Engine 🢒 Engine Controls - 3.1L (LG8) 🢒 Detonation/Spark Knock

Detonation/Spark Knock

Inspection/Test

Action

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

Preliminary
    •  Refer to Intermittent Conditions before starting.
    •  Search for bulletins.

Fuel System
    •  Test the fuel system circuits for proper operation. Refer to Fuel Pump Electrical Circuit Diagnosis .
    •  Test for low fuel pressure. Refer to Fuel System Diagnosis .
    •  Test for faulty fuel injectors. Refer to Fuel Injector Balance Test with Special Tool , Fuel Injector Balance Test with Tech 2 , Fuel Injector Solenoid Coil Test test procedures.
    •  Inspect for fuel contamination. Refer to Alcohol/Contaminants-in-Fuel Diagnosis .
    •  Inspect any items which may cause an engine to run rich, long term fuel trim is significantly in the negative range. Refer to Diagnostic Aids for DTC P0172.
    •  Inspect any items which may cause an engine to run lean, long term fuel trim is significantly in the positive range. Refer to Diagnostic Aids for DTC P0171.

Ignition System

Inspect the spark plugs for proper heat range and reach. Refer to Ignition System Specifications .

    • Inspect for proper ignition voltage output using the following steps:
        1.  Attach the J 26792 spark tester to engine ground.
        2.  Connect the spark plug end of the spark plug wire to the J 26792 . Leave the other end of the spark plug wire connected to the coil being tested.
        3.  Connect the spark plug end of the companion spark plug wire to ground.

The companion spark plug wire is the wire attached to the corresponding coil tower.

        4.  Crank the engine while observing the J 26792 . A spark should be observed.
        5.  Repeat the above steps for each coil.
    •  If spark is not present at the coils, inspect for the following conditions:
       -  Coils--Cracks, carbon tracking/arcing, or a resistance value outside the specified range.

Coil Resistance
5000-8000ohms (5K-8Kohms)

       -  Spark Plug wires--signs of arcing, cross firing, cracks, carbon tracking, plug boot damage, pinched, improper routing, or a resistance value outside the specified range.

Spark Plug Wire Resistance
600ohms per foot (1 968ohms per meter)

    Important: :  Spraying the secondary ignition wires with a light mist of water may help locate an intermittent problem. Ignition voltage will arc to ground when a secondary component is faulty.

       -  Defective ignition module.
       -  Ignition system wiring--Loose ignition module feed or ground connection, or damaged system wiring.
    •  Remove spark plugs and inspect for the following conditions:
       -  Fouled plugs
       -  Cracks
       -  Wear
       -  Improper gap
       -  Burned or damaged electrodes
       -  Improper heat range or reach
    •  If spark plugs are gas or oil fouled, the cause of the fouling must be determined before replacing the spark plugs. Refer to Spark Plug Inspection .

Engine Cooling System

Inspect for obvious overheating problems:

    •  Low engine coolant
    •  Restricted air flow to radiator, or restricted water flow through radiator.
    •  Inoperative electric cooling fan circuits.
    •  Correct coolant solution should be a 50/50 mix. Refer to Cooling System Description and Operation in Engine Cooling.

Engine Mechanical
    •  Excessive oil in combustion chamber--Refer to Oil Consumption Diagnosis in Engine Mechanical.
    •  Low cylinder compression. Refer to Engine Compression Test in Engine Mechanical.
    •  For incorrect basic engine parts. Inspect the following conditions:
       -  Cylinder heads
       -  Camshaft and valve train components
       -  Pistons, etc.

Additional
    •  Test for proper EGR system operation. Refer to DTC P0401 .
    •  Inspect the Transaxle Range Switch input with the vehicle in drive and the gear selector in drive or overdrive.
    •  Test the torque converter clutch (TCC) operation. TCC applying too soon can cause the engine to spark knock. Refer to Torque Converter Diagnosis in Automatic Transaxle.
    •  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 rating of 87 and re-evaluate vehicle performance.