Possible Causes & Corrections
WARNING: This page is about a different car, the 2003 GMC Sierra and 2003 Chevrolet Silverado. However, it is still accessible from the selected car via links, so may be relevant.
Check the following items:
- Low engine coolant level.
- Proper tension on the drive belts.
- Restricted air flow through the radiator or restricted coolant flow.
- Faulty thermostat.
- Check for a correct coolant mixture.
- Inspect for an Engine Coolant Temperature (ECT) sensor that has a shift in value. See DIAGNOSTIC TROUBLE CODE DEFINITIONS in SELF-DIAGNOSTICS - 4.3L SIERRA & SILVERADO article.
- Drive vehicle at the speed of the complaint. Monitoring the fuel trim will help identify the problem.
- If system is lean, the long term fuel trim will be more than 150 on scan tool.
- Check fuel pressure. See FUEL SYSTEMS in BASIC DIAGNOSTIC PROCEDURES - 4.3L SIERRA & SILVERADO article.
- Inspect for a poor fuel quality and a proper octane rating.
- If fuel trim readings are normal and there are no engine mechanical concerns, fill fuel tank with a known-good fuel and re-evaluate vehicle performance.
- Inspect spark plugs for proper heat range and gap.
- Check Knock Sensor (KS) system for excessive spark retard activity.
- Inspect ignition timing.
- Inspect for carbon build up. Remove carbon with a top engine cleaner.
- Test combustion chamber pressure by performing a compression test. See CYLINDER COMPRESSION PRESSURE under MECHANICAL INSPECTION under PRELIMINARY INSPECTION & ADJUSTMENTS in BASIC DIAGNOSTIC PROCEDURES - 4.3L SIERRA & SILVERADO article.
- Check for proper operation of EGR valve. See DIAGNOSTIC TROUBLE CODE DEFINITIONS in SELF-DIAGNOSTICS - 4.3L SIERRA & SILVERADO article.
- Test the Torque Converter Clutch (TCC) operation. See appropriate DIAGNOSIS in AUTOMATIC TRANSMISSIONS. TCC applying too soon can cause engine to spark knock.
- Check Service Bulletins for calibration updates.