Detonation/Spark Knock. GMC Truck GMC C Sierra

For 1990-2009 cars only

Makes 🢒 GMC_Truck 🢒 2004 🢒 GMC C Sierra - 2WD 🢒 Engine 🢒 Engine Controls - 4.8L, 5.3L, and 6.0L 🢒 Detonation/Spark Knock

Inspection/Tests

Action

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

Preliminary Inspections

•	Refer to Important Preliminary Inspections Before Starting in Symptoms - Engine Controls .

•	Search for bulletins.

•	Verify that the powertrain control module (PCM) grounds are clean, tight, and in the proper locations. Refer to Power and Grounding Component Views in Wiring Systems and Engine Controls Schematics .

•	If there are no engine mechanical faults, fill the fuel tank with a known high quality fuel that meets the vehicles minimum octane requirements. Road test the vehicle and re-evaluate the vehicles performance.

Fuel System

•	Inspect for incorrect fuel pressure. Refer to Fuel System Diagnosis .

•	Inspect for a contaminated fuel condition. Refer to Alcohol/Contaminants-in-Fuel Diagnosis .

•	Inspect for the following conditions that may cause the engine to run lean:

Notice: Refer to Heated Oxygen and Oxygen Sensor Notice in the Preface section.

-	Water intrusion in the heated oxygen sensor (HO2S) connector

-	An exhaust leak between the HO2S and the engine--Refer to Exhaust Leakage in Engine Exhaust.

-	Vacuum leaks

-	Incorrect fuel pressure--Refer to Fuel System Diagnosis .

-	Restricted fuel injectors--Refer to Fuel Injector Balance Test with Special Tool or Fuel Injector Balance Test with Tech 2 .

-	An inaccurate mass air flow (MAF) sensor

-	Fuel contamination--Refer to Alcohol/Contaminants-in-Fuel Diagnosis .

-	Vacuum hoses that are split, kinked, or improperly connected

Ignition System

Verify that the spark plugs are of the proper heat range. Refer to Spark Plug Inspection .

Engine Cooling System

Inspect for obvious overheating problems:

•	Low engine coolant--Refer to Loss of Coolant in 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.

•	Inoperative cooling fan--Refer to Fan Clutch Diagnosis in Engine Cooling.

Engine Mechanical

Inspect for the following engine mechanical problems:

•	Excessive oil in combustion chamber--Leaking valve seals. Refer to Oil Consumption Diagnosis in Engine Mechanical.

•	Low cylinder compression--Refer to Engine Compression Test in Engine Mechanical.

•	Combustion chambers for excessive carbon buildup--Clean the combustion chamber by using top engine cleaner. Follow the instructions on the can.

•	Inspect for incorrect basic engine parts. Inspect the following:

-	The camshaft--Refer to Camshaft and Bearings Cleaning and Inspection in Engine Mechanical.

-	The cylinder heads--Refer to Cylinder Head Cleaning and Inspection in Engine Mechanical.

-	The pistons, etc.--Refer to Piston, Connecting Rod, and Bearing Cleaning and Inspection in Engine Mechanical.

•	Refer to Symptoms - Engine Mechanical in Engine Mechanical.

Additional Inspections

•	Inspect the park/neutral position (PNP) switch operation. Refer to Diagnostic System Check - Automatic Transmission in Automatic Transmission-4L60-E.

•	Inspect the transmission torque converter clutch (TCC) operation. The TCC applying too soon can cause the engine to spark knock. Refer to Diagnostic System Check - Automatic Transmission in Automatic Transmission-4L60-E.