GM Service Manual Online
For 1990-2009 cars only

Fuel Knock/Combustion Noise EFI

Checks

Action

Definition: A mild to severe ping which is usually worse upon acceleration. The engine makes sharp metallic knocks which change with the throttle opening.

Preliminary Checks

    • Refer to Symptoms .
    • Make sure the vehicle has an actual problem.
    • Check the fuel quality. Refer to Fuel Quality Diagnosis .

Cooling System Checks

    • Check for obvious overheating problems. Refer to the appropriate service manual.
    • Check for a low engine coolant level.
    • Check for a loose water pump belt.
    • Check for restricted air flow through the radiator, or restricted coolant flow.
    • Check for a malfunctioning or incorrect thermostat.
    • Check for a correct coolant solution. The solution should be a 50/50 mix of anti-freeze and water.

Fuel System Checks

    • Check for air leaks in the fuel supply to the injection pump. Refer to Fuel Supply System Check .
    • Check the injection pump static timing. Refer to Fuel Injection Pump Timing Adjustment .
    • Check the injection nozzles. Refer to Injection Nozzle(s) Diagnosis .

Engine Mechanical Checks

    • Check for incorrect basic engine parts such as the cam, the heads, the pistons, etc.
    • Check for any excessive oil entering the combustion chamber.

Additional Checks

Check the Service Bulletins for control module software updates.

Fuel Knock/Combustion Noise MFI

Checks

Action

Definition: A mild to severe ping which is usually worse upon acceleration. The engine makes sharp metallic knocks which change with the throttle opening.

Preliminary Checks

    • Refer to Symptoms .
    • Make sure the vehicle has an actual problem.
    • Check the fuel quality. Refer to Fuel Quality Diagnosis .

Cooling System Checks

    • Check for obvious overheating problems. Refer to the appropriate service manual.
    • Check for a low engine coolant level.
    • Check for a loose water pump belt.
    • Check for restricted air flow through the radiator, or restricted coolant flow.
    • Check for a malfunctioning or incorrect thermostat.
    • Check for a correct coolant solution. The solution should be a 50/50 mix of anti-freeze and water.

Fuel System Checks

    • Check for air leaks in the fuel supply to the injection pump. Refer to Fuel Supply System Check .
    • Check the injection pump static timing. Refer to Fuel Injection Pump Timing Adjustment .
    • Check the injection nozzles. Refer to Injection Nozzle(s) Diagnosis .

Engine Mechanical Checks

    • Check for incorrect basic engine parts such as the cam, the heads, the pistons, etc.
    • Check for any excessive oil entering the combustion chamber.

Additional Checks

Check the Service Bulletins for control module software updates.