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:
- Test for a cylinder misfire. Start engine and allow to stabilize. DO NOT perform this test for more than 2 minutes to prevent damaging catalytic converter. Perform Cylinder Power Balance Test with a scan tool. If there is an RPM drop on all cylinders, equal to within 50 RPM, refer to ROUGH, UNSTABLE OR INCORRECT IDLE AND STALLING . If there is no spark, refer to NO-START- ENGINE CRANKS OKAY under NO-START DIAGNOSIS in BASIC DIAGNOSTIC PROCEDURES - 4.2L BRAVADA, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article. If there is spark, remove spark plugs in affected cylinders and inspect for insulation cracks, wear, improper gap, burned electrodes, or heavy deposits. Check ignition system for moisture, dust, cracks, burns, etc.
- Perform Fuel Injector Balance Test. Refer to FUEL SYSTEMS in SYSTEM & COMPONENT TESTING - 4.2L BRAVADA, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article.
- Perform a cylinder compression check. See CYLINDER COMPRESSION PRESSURE under MECHANICAL INSPECTION under PRELIMINARY INSPECTION & ADJUSTMENTS in BASIC DIAGNOSTIC PROCEDURES - 4.2L BRAVADA, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article.
- Inspect the engine for improper valve timing, worn rocker arms, worn camshaft lobes, broken or weak valve springs, and intake and exhaust manifold passages for casting flash.
- Test fuel pressure. Refer to FUEL SYSTEMS in BASIC DIAGNOSTIC PROCEDURES - 4.2L BRAVADA, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article.
- Inspect for water contamination in fuel.
- Perform the fuel injector coil test. Refer to FUEL SYSTEMS in SYSTEM & COMPONENT TESTING - 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.