GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Buick 🢒 2000 🢒 GL7 (Export) 🢒 Engine 🢒 Engine Controls - 3.0L (LW9) 🢒 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 for low fuel pressure. Refer to Fuel System Pressure Test .
    •  Test for contaminated fuel. Refer to Alcohol/Contaminants-in-Fuel Diagnosis .
    •  Inspect the items that can cause an engine to run lean. Refer to Diagnostic Aids in DTC P0172 Fuel Trim System Rich .

Ignition System

Inspect the spark plugs for proper heat range and reach.

    • 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 spark tester; 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 spark tester; 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.

Engine Cooling System

Inspect for obvious overheating problems:

    •  A low engine coolant level
    •  A restricted air flow to the radiator, or restricted water flow through the radiator
    • Any inoperative electric cooling fan circuits
    •  The correct coolant solution should be a 50/50 mix. Refer to Coolant Description in Engine Cooling.

Engine Mechanical
    • Excessive oil in the combustion chambers and leaking valve seals. Refer to Base Engine Misfire Diagnosis in Engine Mechanical.
    •  A low cylinder compression. Refer to Engine Compression Test in Engine Mechanical.
    •  Excessive carbon buildup in the combustion chambers. Clean using Top engine cleaner. Follow the instructions on the can.
    •  Inspect the following components for incorrect basic engine parts. Refer to Base Engine Misfire Diagnosis in Engine Mechanical:
       -  The camshaft
       -  The cylinder heads
       -  The pistons, etc.

Additional
    •  Inspect for correct EGR system operation. Refer to DTC P0401 Exhaust Gas Recirculation (EGR) Flow Insufficient .
    •  Test the transaxle range switch input with the vehicle in Drive and the gear selector in Drive or Overdrive.
    •  Test the TCC operation. The TCC applying too soon can cause the engine to spark knock. Refer to Torque Converter Diagnosis in Automatic Transaxle-4T65-E.
    •  If the 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 the vehicle performance.