Detonation/Spark Knock. Buick GL7 (Export) 2000

For 1990-2009 cars

#### Detonation/Spark Knock

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

Preliminary

• | Refer to Powertrain On Board Diagnostic (OBD) System Check .

• | 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.