Detonation/Spark Knock
Checks
| Action
|
DEFINITION: A mild to severe ping,
usually worse under acceleration. The engine makes sharp metallic knocks
that change with throttle opening.
|
Preliminary Checks
|
| • | Search for service bulletins. |
|
Fuel System
|
| • | Check for contaminated fuel. Refer to Alcohol/Contaminants-in-Fuel Diagnosis
. |
| • | Check items that can cause an engine to run lean (long term fuel
trim significantly in the positive range). Refer to Diagnostic Aids for
DTC P0171 Fuel Trim System Lean
. |
|
Ignition System
|
| • | Check the spark plugs for proper heat range and reach. |
| • | Check the Knock Sensor (KS) system for no retard timing. |
|
Engine Cooling System
| Check for obvious overheating problems:
| • | Restricted air flow to radiator, or restricted water flow through
radiator. |
| • | Inoperative electric cooling fan circuits. |
| • | Correct coolant solution should be a 50/50 mix of Dexcool or equivalent
antifreeze coolant and water. |
|
Engine Mechanical
|
| • | Excessive oil in combustion chamber-leaking valve seals. Refer
to Oil Consumption Diagnosis
in Engine Mechanical. |
| • | Combustion chambers for excessive carbon buildup. Clean using
top engine cleaner. Follow instructions on can. |
| • | For incorrect basic engine parts. Inspect the following: |
| • | Refer to the Engine Mechanical portion of the service manual. |
|
Additional Checks
|
- Check the Park/Neutral Position (PNP) switch input with the vehicle
in drive and the gear selector in drive or overdrive.
- Check Torque Convertor Clutch operation. TCC applying too soon
can cause the engine to spark knock. Refer to
Torque Converter Diagnosis
in Automatic Transmission 4L60-E.
- If scan tool readings are normal and there are no engine mechanical
malfunctions, fill the fuel tank with a known quality gasoline that has a
minimum octane reading of 87 and re-evaluate vehicle performance.
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