GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 1998 🢒 Chevy P12 Chassis 🢒 Engine 🢒 Engine Controls - 7.4L 🢒 Detonation/Spark Knock

Checks

Action

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

Preliminary Checks
    • Refer to Symptoms , Important Preliminary Checks Before Starting.
    • Search for bulletins.
    • Check the PCM grounds for being clean, tight, and in their proper locations. Refer to PCM wiring diagrams .
    • If the scan tool readings are normal (refer to supporting text of the Powertrain On-Board Diagnostic (OBD) System Check) and there are no engine mechanical faults, fill the fuel tank with a regular unleaded gasoline rated at 87 octane or higher and re-evaluate the vehicle's performance.

Fuel System
    • Check for a low fuel pressure condition. Refer to Fuel System Diagnosis .
    • Check for a restricted fuel filter. Refer to Fuel System Diagnosis .
    •  Check for a contaminated fuel condition. Refer to Alcohol/Contaminants-in-Fuel Diagnosis .
    • Check the items which can cause an engine to run rich (long term fuel trim near -13%). For a rich condition, refer to DTC P0132 HO2S Circuit High Voltage Bank 1 Sensor 1 and DTC P0152 HO2S Circuit High Voltage Bank 2 Sensor 1 .
    • Check the items that can cause an engine to run lean (long term fuel trim near 23%). For a Lean condition, refer to DTC P0131 HO2S Circuit Low Voltage Bank 1 Sensor 1 and DTC P0151 HO2S Circuit Low Voltage Bank 2 Sensor 1 .

Ignition System
    • Check the spark plugs for being the proper heat range. Refer to Engine Electrical/Spark Plugs .
    • Check the Knock Sensor (KS). Refer to Knock Sensor (KS) System Diagnosis .

Engine Cooling System

Check for obvious overheating problems:

    • Low engine coolant. Refer to Engine/Engine Cooling for the type and amount of engine coolant to be used.
    • Restricted air flow to the radiator or restricted coolant flow through the radiator.
    • Check for the proper tension on the drive belts.
    • Check for a faulty thermostat. Refer to Diagnosis of the Thermostat in Engine Cooling .
    • Check for a correct coolant solution. The coolant should be a 50/50 mix of antifreeze and water.

Engine Mechanical

Check for the following engine mechanical problems:

    • Excessive oil in combustion chamber-Leaking valve seals. Refer to Engine/Engine Mechanical.
    • Low cylinder compression. Refer to Engine/Engine Mechanical .
    • Combustion chambers for excessive carbon buildup. Clean the combustion chamber by using top engine cleaner. Follow the instructions on the can.
    • Check for incorrect basic engine parts. Inspect the following:
       - Camshaft
       - Cylinder heads
       - Pistons, etc.
    • Refer to Engine/Engine Mechanical.

Additional Checks
    • Check the Park/Neutral Position (PNP) switch operation. Refer to Park/Neutral Position (PNP) Switch System Diagnosis .
    • Check for proper EGR operation of the EGR Valve. Refer to EGR System Diagnosis .
    • Check for the proper operation of the Air Intake System. Refer to Air Induction System .