For 1990-2009 cars

#### Detonation/Spark Knock

Inspection/Tests | Action
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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 engine control module (ECM) grounds are clean, tight, and in the proper locations. Refer to Power and Grounding Component Views 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 restricted fuel filter. Refer to Fuel System 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 .

- | Vacuum leaks.

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

- | Restricted fuel injectors. Refer to Customer Concern Verification Sheets or Customer Concern Verification Sheets .

- | An inaccurate mass air flow (MAF) sensor.

- | Vacuum hoses that are split, kinked, or incorrectly 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 , 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 Cooling Fan Inoperative .

Engine Mechanical | Inspect for the following engine mechanical problems:

• | Excessive oil in combustion chamber. Leaking valve seals. Refer to Oil Consumption Diagnosis .

• | Low cylinder compression. Refer to Engine Compression Test .

• | 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 .

- | The cylinder heads. .Refer to Cylinder Head Cleaning and Inspection .

- | The pistons, etc. Refer to Piston, Connecting Rod, and Bearing Cleaning and Inspection .

• | Refer to Symptoms - Engine Mechanical .

Additional Inspections |

• | Inspect the park/neutral position (PNP) switch operation.

• | Inspect the transmission torque converter clutch (TCC) operation. The TCC applying too soon can cause the engine to spark knock. Refer to Torque Converter Diagnosis .