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
|
| • | Refer to Symptoms, Important Preliminary Checks
Before Starting.
|
| • | Check PCM grounds for being clean, tight and in their proper locations. |
| • | If the scan tool readings are normal (refer to supporting text
of the Powertrain On-Board Diagnostic (OBD) System Check) and there
are no engine mechanical faults. Fill the fuel tank with a premium gasoline
that has a minimum octane reading of 92 and re-evaluate vehicle performance. |
|
Fuel System
|
| • | Check for low fuel pressure. Refer to Fuel Pressure Check. |
| • | Check for restricted fuel filter. |
| • | Check for contaminated fuel. Refer to Fuel Quality Diagnosis. |
| • | Check items which can cause an engine to run rich (long term fuel
trim near -99%). |
| • | Check items that can cause an engine to run lean (long term fuel
trim near 100%). |
|
Ignition System
| Spark plugs for proper heat range. Refer to Owners Manual or General Information.
|
Engine Cooling System
| Check for obvious overheating problems:
| • | Restricted air flow to radiator, or restricted water flow through
radiator. |
| • | Inoperative electric cooling fan circuit(s). |
| • | Refer to Engine Cooling
. |
|
Engine Mechanical
|
| • | Excessive oil in combustion chamber -- Leaking valve seals.
Refer to Engine Mechanical.
|
| • | Low cylinder compression. Refer to Engine Mechanical.
|
| • | Combustion chambers for excessive carbon buildup. Clean using
Top engine cleaner. Follow instructions on container. |
| • | For incorrect basic engine parts. Inspect the following: |
Refer to Engine Mechanical.
|
Additional Checks
|
| • | Check Park/Neutral Position (PNP) switch operation. Connect scan
tool and monitor PNP signal. The scan tool should indicate P-N----
when in park or neutral and -R-OD21 when in any forward gear
or reverse. |
| • | Check TCC operation. TCC applying too soon can cause the engine
to spark knock. Refer to Transmission Controls.
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