Detonation/Spark Knock

Definition: A mild to severe ping, usually worse under acceleration. The engine makes sharp metallic knocks that change with throttle opening. Sounds like popcorn popping.


PRELIMINARY CHECKS

^ Perform the careful visual/physical checks as described at start of "Symptoms,".

^ Park/Neutral position switch. Be sure "Scan tool" indicates drive with gear selector in drive or overdrive. Use CHART C-1A.

^ If "Scan tool" readings are normal and there are no engine mechanical faults, fill fuel tank with a gasoline that has a minimum octane reading of 87 and revaluate vehicle performance.

^ CHECK: Exhaust gas recirculation system for not opening. Use CHART C-7.


COOLING SYSTEM

^ Check for obvious overheating problems:

- Low engine coolant.

- Restricted air flow to radiator, or restricted water flow through radiator.

- Correct engine coolant solution should be a 50/50 mix of anti-freeze engine coolant (or equivalent) and water.


FUEL SYSTEM

^ NOTICE: To determine if the condition is caused by a rich or lean system, the car should be driven at the speed of the complaint. Monitoring L.T. Fuel Trim will help identify problem.

Lean- L.T. Fuel Trim above 142. Refer to "Diagnostic Aids" for diagnostic trouble code 44.

Rich - L.T. Fuel Trim below 118. Refer to "Diagnostic Aids" for diagnostic trouble code 45.

^ CHECK: Fuel pressure, use CHART A-7.

IGNITION SYSTEM

^ CHECK: Spark plugs for proper heat cause. Refer to Owner's Manual.

^ CHECK: Ignition timing, using a "Scan tool".


ENGINE MECHANICAL

^ CHECK: For excessive oil in the combustion chamber.

- Valve oil seals for leaking.

^ CHECK: Combustion chambers for excessive carbon build up. 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.