GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 1997 🢒 Savana 🢒 Engine 🢒 Engine Controls - 5.0L, 5.7L, and 7.4L 🢒 Detonation/Spark Knock

Check

Action

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

Preliminary Checks
    • Refer to Important Preliminary Checks .
    • Make sure the customer has an actual problem.
    • Check the Transmission Range (TR) pressure switch assembly operation. Refer to Transmission Fluid Pressure Switch Assembly.

Cooling System Checks
    • Check for an obvious overheating problem. Refer to the Diagnosis of the Cooling System in Engine Cooling.
    • Check for a low engine coolant level.
    • Check for the proper tension on the drive belts.
    • Check for restricted air flow through the radiator, or restricted coolant flow.
    • 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.

Sensor Check

Check for an Engine Coolant Temperature (ECT) sensor that has a shift in value. Refer to DTC P1115 Engine Coolant Temperature (ECT) Sensor Circuit Intermittent High Voltage Diagnostic Aids. Refer to DTC P0118 Engine Coolant Temperature (ECT) Sensor Circuit High Voltage Diagnostic Aids.

Fuel System Checks
    • Check if a Lean system causes this condition. Drive the vehicle at the speed of the complaint. Monitoring the Fuel Trim will help identify the problem.
    • If the system is Lean, the Long Term Fuel Trim will be greater than 150. Refer to DTC P0132 HO2S Circuit High Voltage Bank 1 Sensor 1 Diagnostic Aids. Refer to DTC P0138 HO2S Circuit High Voltage Bank 1 Sensor 2 Diagnostic Aids.
    • Check the fuel pressure. Refer to Fuel System Diagnosis .
    • Check for a poor fuel quality and a proper octane rating.
    • If the scan tool readings are normal and there are no engine mechanical faults, fill the fuel tank with a premium gasoline that has a minimum octane rating of 92 and re-evaluate the vehicle's performance.

Ignition System Checks
    • Check the spark plugs for their proper heat range and gap.
    • Check the Knock Sensor (KS) system operation. Refer to DTC P0327 Knock Sensor (KS) Circuit .
    • Check the ignition timing. Refer to Setting Timing for the 4.3L. Refer to Setting Timing for the 5.0L, 5.7L, 7.4L.

Engine Mechanical Checks
    • Check for carbon build up. Remove the carbon with a top engine cleaner. Follow the instructions on the can.
    • Check the combustion chamber pressure by performing a compression test. Refer to Engine Mechanical.

Additional Checks
    • Check for the proper operation of the EGR Valve. Refer to Exhaust Gas Recirculation (EGR) System Diagnosis .
    • Check for the proper operation of the Air Intake system. Refer to Air Induction System .
    • Check for the proper operation of the transmission shift points. Refer to the Transmission Controls section.
    • Check the Torque Converter Clutch (TCC) operation. Refer to Torque Converter Clutch Solenoid in Automatic Transmission.
    • Check the Service Bulletins for PROM updates.