Detonation/Spark Knock. GMC Truck GMC C-Series Medium Duty Truck B7 1998

For 1990-2009 cars only

Makes 🢒 GMC_Truck 🢒 1998 🢒 GMC C-Series Medium Duty Truck B7 🢒 Engine 🢒 Engine Controls - 6.0L and 7.0L 🢒 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 for the Important Preliminary Checks.

•	Make sure the customer has an actual problem.

•	Check for fuel spray from both injectors. Refer to Engine Cranks but Does Not Run .

•	Check the neutral switch. Refer to Neutral Switch Diagnosis - Automatic Transmission Only .

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 faulty or incorrect thermostat.

•	Check for a correct coolant solution. The solution should be a 50/50 mix of anti-freeze and water.

Sensor Check

Check for an Engine Coolant Temperature (ECT) sensor that has a shift in value. Refer to the Diagnostic Aids in DTC 15 ECT Sensor Circuit High .

Fuel System Checks

•	Determine if a lean system is causing the 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 the Diagnostic Aids in DTC 44 Lean Exhaust Indicated .

•	Check the fuel pressure. Refer to Fuel System Diagnosis .

•	Check for poor fuel quality and proper octane rating. Fill the fuel tank with a premium gasoline that has a minimum octane rating of 92 and re-evaluate vehicle performance if the scan tool readings are normal and there are no engine mechanical faults.

Ignition System Checks

•	Check the spark plugs for their proper heat range and gap.

•	Check the Knock Sensor (KS) system operation. Refer to Knock Sensor (KS) System Diagnosis .

•	Check the ignition timing. Refer to Distributor Ignition (DI) System Diagnosis .

Engine Mechanical Checks

•	Check for carbon buildup. Remove the carbon with a top engine cleaner. Follow the instructions on the can.

•	Check for the incorrect basic engine parts such as cam, heads, pistons, etc. Refer to the appropriate service manual.

•	Check for excessive oil entering the combustion chamber.

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 cleaner. Refer to Air Intake System Diagnosis .

•	Check for the proper transmission shift points. Refer to Transmission/Transaxle.

•	Check the Service Bulletins for PROM updates.