Possible Causes & Corrections
WARNING: This page is about a different car, the 2003 Oldsmobile Bravada, 2003 GMC Envoy XL, 2003 GMC Envoy, and 2003 Chevrolet TrailBlazer. However, it is still accessible from the selected car via links, so may be relevant.
Check the following items:
- Compare customer vehicle with a similar unit. Verify the customer's concern.
- Remove air filter and check for dirt or a restriction.
- Inspect transmission shift pattern and downshift operation.
- Inspect for a restricted fuel filter, contaminated fuel, or improper fuel pressure. Refer to FUEL SYSTEMS in BASIC DIAGNOSTIC PROCEDURES - 4.2L BRAVADA, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article.
- Perform the fuel injector balance test. Refer to FUEL SYSTEMS in SYSTEM & COMPONENT TESTING - 4.2L BRAVADA, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article.
- Inspect exhaust system for a possible restriction.
- Inspect exhaust system for damaged or collapsed pipes. Inspect the muffler for heat distress or a possible internal failure.
- Inspect control module grounds for being clean, tight, and in their proper location.
- Inspect Torque Converter Clutch (TCC) operation. See appropriate DIAGNOSIS article in AUTOMATIC TRANSMISSIONS.
- Inspect A/C operation.
- Test generator output voltage.
- Monitor Knock Sensor (KS) system for retarded timing.
- Engine compression. See CYLINDER COMPRESSION PRESSURE under MECHANICAL INSPECTION under PRELIMINARY INSPECTION & ADJUSTMENTS in BASIC DIAGNOSTIC PROCEDURES - 4.2L BRAVADA, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article. Low compressions can be caused by faulty valve timing or improper or worn camshaft.
- Camshaft Phaser for proper operation.