Detonation/Spark Knock/Pings

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

PRELIMINARY CHECKS
Perform the careful visual and physical checks as described in Preliminary Checks. - Important Preliminary Checks

^ Make sure the customer has an actual problem.

^ Remove air filter and check for dirt or for being plugged. Replace as necessary.

^ If there is spray from only one injector, then, there is a malfunction in the injector assembly, or in the signal to the injector assembly. The malfunction can be isolated, by switching the injector connectors. If the problem remains with the original injector, after switching the connector, the injector is defective. Replace the injector. If the problem moves with the injector connector, the problem is an improper signal in the injector circuits, refer to Chart A-3 Engine Cranks But Will Not Run. Related Tests, Information and Procedures

COOLING SYSTEM
Check: For obvious overheating problems. Refer to Cooling System/Testing and Inspection. Cooling System

Check: Engine cooling fan(s) operation.

Check: Low engine coolant.

Check: Loose water pump belt.

Check: Restricted air flow to radiator, or restricted water flow through radiator.

Check: Faulty or incorrect thermostat.

Check: Correct coolant solution - should be a 50/50 mix of GM # 1052753 anti-freeze coolant (or equivalent) and water.

SENSOR
Check: Engine Coolant Temperature (ECT) sensor which has shifted in value. Compare ECT resistance to the chart under "Diagnostic Aids" in Diagnostic Trouble Code (DTC) 15 chart. Powertrain Controls - ECM/PCM

FUEL SYSTEM
NOTE: To determine if the condition is caused by a rich or lean 02S signal, the vehicle should be driven at the speed of the complaint. Monitoring long term fuel trim will help identify the problem.

Lean - Long term fuel trim greater than 150. Refer to "Diagnostic Aids" in DTC 44. Powertrain Controls - ECM/PCM

Rich - Long term fuel trim less than 115. Refer to "Diagnostic Aids" in DTC 45. Powertrain Controls - ECM/PCM

Check: Fuel pressure, refer to Chart A-7 Fuel System Diagnosis. Related Tests, Information and Procedures

Check: For poor fuel quality, proper octane rating.

NOTE: If scan tool readings are normal (see typical Tech 1 scanner values) and there are no engine mechanical faults, fill fuel tank with a premium gasoline that has a minimum octane rating of 92 and re-evaluate vehicle performance. Scan Tool Testing and Procedures

IGNITION SYSTEM
Check: Spark plugs for proper heat range.

Check: Knock Sensor system operation. Refer to Chart C-5 Knock Sensor (KS) System. Chart C-5 Knock Sensor (KS) System Check

Check: Ignition timing. Refer to underhood "Vehicle Emission Control Information" label.

ENGINE MECHANICAL
Check: For carbon buildup. Remove carbon with top engine cleaner. Follow instructions on can.

Check: For incorrect basic engine parts such as cam, heads, pistons and other related engine parts.

Check: For excessive oil entering combustion chamber.

ADDITIONAL CHECKS
Check: Proper operation of air cleaner diaphragm motor.

Check: For proper transmission shift points.

Check: [1][2]Torque Converter Clutch operation. Refer to Chart C-8 Torque Converter Clutch System. Chart C-8 Torque Converter Clutch (TCC) Diagnosis

Check: For correct PROM. Refer to PROM - Programmable Read Only Memory. PROM - Programmable Read Only Memory

Check: For cooling fan operation. Refer to Chart C-12 Electric Cooling Fan Control Circuit Diagnosis if equipped with electric cooling fans. Chart C-12 Coolant Fan Control Circuit

Check: EGR valve operation. Refer to Chart C-7 Exhaust Gas Recirculation Check. Chart C-7 EGR System Check