Possible Causes & Corrections
WARNING: This page does not describe the selected car, but rather 7 other vehicles, including the 2003 GMC Yukon XL, 2003 GMC Sierra, 2003 GMC Cab & Chassis Sierra, 2003 Chevrolet Suburban, and 2003 Chevrolet Silverado. However, it is still accessible from the selected car via links, so may be relevant.
Check for the following items:
- Search for bulletins.
- Verify that PCM grounds are clean, tight and in the proper locations.
- Check fuel pressure. See FUEL SYSTEM PRESSURE TEST under FUEL SYSTEMS in BASIC DIAGNOSTIC PROCEDURES - 8.1L AVALANCHE, SIERRA, SILVERADO, SUBURBAN & YUKON XL article.
- Inspect for a restricted fuel filter.
- Inspect for a contaminated fuel condition.
- Verify that both fuel injector fuses are not open. An open fuel injector fuse causes 4 ignition coils and 4 fuel injectors not to operate. Inspect ignition coil circuits and fuel injector circuits for an intermittent short to ground.
- Inspect fuel injectors. Refer SYSTEM & COMPONENT TESTING - 8.1L AVALANCHE, SIERRA, SILVERADO, SUBURBAN & YUKON XL article.
- Inspect cause for engine to run rich: Water intrusion in HO2S connector, engine oil contaminated by fuel, EVAP canister purge condition, incorrect fuel pressure, leaking fuel pressure regulator, leaking fuel injectors, inaccurate MAF sensor, blockage on MAF sensor inlet screen, vacuum hoses that are split, kinked, or improperly connected, air intake duct that is collapsed or restricted, or an air filter that is dirty or restricted.
- Inspect cause for engine to run lean: Water intrusion in HO2S connector, exhaust leak between HO2S and engine, vacuum leaks, incorrect fuel pressure, restricted fuel injectors, inaccurate MAF sensor, fuel contamination, or vacuum hoses that are split, kinked, or improperly connected.
- Soak the secondary ignition system with water from a spray bottle. Soaking the secondary ignition system may help locate damaged or deteriorated components. Look and listen for arcing or misfiring as you apply water.
- Test for proper ignition voltage output with Spark Tester (J-26792).
- Remove spark plugs and check for correct heat range, wet plugs, cracks, wear, improper gap, burned electrodes or heavy deposits.
- An improper spark plug gap will cause a driveability problem. Gap spark plugs using a wire gauge gap tool.
- Determine cause of the fouling before replacing spark plugs.
- Using scan tool, monitor the Misfire Current Counters while driving the vehicle in the conditions that the misfire occurred. If a misfiring cylinder can be located, use DTC P0300 diagnostic procedures for diagnosis. See DIAGNOSTIC TROUBLE CODE DEFINITIONS in SELF-DIAGNOSTICS - 8.1L AVALANCHE, SIERRA, SILVERADO, SUBURBAN & YUKON XL article.
- Inspect for loose ignition coil grounds.
- Inspect engine thermostat for proper operation and for proper heat range.
- Inspect generator output voltage. Repair charging system if generator output voltage is less than 9 volts or more than 16 volts.