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/physical checks as described in "PRELIMINARY CHECKS". Testing and Inspection
^ Check Park/Neutral Position (PNP) or trans range switch. Be sure Tech-1 scan tool indicates drive with gear selector in drive or overdrive. Refer to "DIAGNOSTIC CHARTS/C-CHARTS/CHART C-1A PARK NEUTRAL POSITION - TRANS RANGE SWITCH DIAGNOSIS". Chart C-1A Park/Neutral Switch Diagnosis

^ Using a tech-1 scan tool, read/record sensor data and compare with normal values. Refer to "SCAN TOOL DIAGNOSITICS/TYPICAL SCAN DATA VALUES" Scan Tool Data List If tech-1 scan tool readings are normal, and there are no engine mechanical faults, fill fuel tank with a premium gasoline that has a minimum octane reading of 92 and re-evaluate vehicle performance.
^ Check service Bulletins updates. Check for correct EPROM.

COOLING SYSTEM
^ Check for obvious overheating problems:
- Low engine coolant.
- Loose water pump belt.
- Restricted air flow to radiator, or restricted water flow through radiator.
- Inoperative electric cooling fan circuit. Refer to "DIAGNOSTIC CHARTS/C-CHARTS/CHART C-12 COOLANT FAN FUNCTIONAL CHECK". Chart C-12 Coolant Fan Functional Check
- Correct coolant solution should be a 50/50 mix of GM #1052753 anti-freeze coolant or equivalent and water.

IGNITION SYSTEM
^ Check Knock Sensor (KS) system for no retard. Refer to "DIAGNOSTIC CHARTS/C-CHARTS/CHART C-5 KNOCK SENSOR (KS) SYSTEM CHECK". Chart C-5 Knock Sensor (KS) System Check

ENGINE MECHANICAL
^ Check for excessive oil consumption (leaking valve ol seals)
^ Check for excessive carbon build up in combustion chamber. Remove carbon with top engine cleaner and follow instructions on can.
^ Check combustion chamber pressure by performing a compression test.
^ Check for incorrect basic engine parts such as cam, heads, pistons, etc.
^ Check spark plugs for correct heat range and proper torque.

FUEL SYSTEM

NOTE: To determine if the condition is caused by a rich or lean system, the vehicle should be driven at the speed of the complaint. Monitoring long term fuel trim will help identify a problem. Long term fuel trim for a normal running engine is near 128.

^ Long term fuel trim near 198 is a rich command compensating for a lean running engine. If the engine is very lean, a long term fuel trim of 198 may not fully compensate for the lean condition, resulting in driveability symptoms.
^ Long term fuel trim near 58 is a lean command compensating for a rich running engine. If the engine is very rich, a long term fuel trim of 58 may not fully compensate for the rich condition, resulting in driveability symptoms.

^ Check fuel pressure. Refer to "DIAGNOSTIC CHARTS/A-CHARTS/CHART A-7 FUEL SYSTEM DIAGNOSIS".
^ Check in-line fuel fllter. Replace if dirty or plugged.
^ Check fuel injectors. Perform injector coil/balance test. Refer to "DIAGNOSTIC CHARTS/C-CHARTS/CHART C-2A FUEL INJECTOR TESTING". Chart C-2A Fuel Injector Balance Test
^ Check for contaminated fuel.

ADDITIONAL CHECKS
^ Check TCC operation, TCC applying too soon (if equipped). Refer to "DIAGNOSTIC CHARTS/C-CHARTS/CHART C-8 TRANSMISSION DIAGNOSIS". Chart C-8 Transmission Diagnosis
^ Check for intake valve deposits.