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 the following items:

Search for bulletins.
Verify that PCM grounds are clean, tight and in the proper locations.
Inspect the owner's driving habits. Is the A/C ON or the defroster mode ON full time? Are the tires at the correct pressure? Are the wheels and tires the correct size? Are there excessively heavy loads being carried? Is the acceleration rate too much, too often? Remove air filter element and inspect for dirt or for restrictions. Replace as necessary.
Inspect the type, quality and alcohol content of fuel. Oxygenated fuels have lower energy and may deliver reduced fuel economy.
Inspect fuel injectors. See SYSTEM & COMPONENT TESTING - 8.1L AVALANCHE, SIERRA, SILVERADO, SUBURBAN & YUKON XL article.
Inspect for incorrect 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.
Ensure that each fuel injector harness is connected to the correct injector and cylinder. Relocate the injector harnesses as necessary.
Inspect for foreign material accumulation in the throttle bore, coking on the throttle valve, or on the throttle shaft.
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 air filter that is dirty or restricted.
Inspect air intake system and crankcase for air leaks.
Inspect crankcase ventilation valve for proper operation. See EMISSION SYSTEMS & SUB-SYSTEMS in SYSTEM & COMPONENT TESTING - 8.1L AVALANCHE, SIERRA, SILVERADO, SUBURBAN & YUKON XL article.
Inspect for an inaccurate speedometer.
Use scan tool in order to monitor the Knock Sensor (KS) system for excessive spark retard activity.
Inspect for proper ignition voltage output with Spark Tester (J-26792).
Remove spark plugs and inspect for wet plugs, cracks, wear, improper gap, burned electrodes or heavy deposits.
An improper spark plug gap will cause a driveability problem.
Determine the cause of fouling before replacing spark plugs.
Visually and physically inspect the secondary ignition for ignition wires arcing to ground or ignition wires for proper routing.
Soaking the secondary ignition system with water from a spray bottle may help locate damaged or deteriorated components. Look and listen for arcing or misfiring as you apply water.
Inspect for loose ignition coil grounds. See ELECTRONIC IGNITION SYSTEM DIAGNOSIS under IGNITION SYSTEMS in SYSTEM & COMPONENT TESTING - 8.1L AVALANCHE, SIERRA, SILVERADO, SUBURBAN & YUKON XL article.
Inspect for low engine coolant level.
Inspect engine thermostat for proper operation and for correct heat range.
Inspect engine mechanical for compression, sticking or leaking valves, worn camshaft lobes, valve timing, bent push rods, worn rocker arms, broken valve springs or excessive oil in combustion chamber, caused by leaking valve seals. See CYLINDER COMPRESSION PRESSURE under MECHANICAL INSPECTION under PRELIMINARY INSPECTION & ADJUSTMENTS in BASIC DIAGNOSTIC PROCEDURES - 8.1L AVALANCHE, SIERRA, SILVERADO, SUBURBAN & YUKON XL article.
Inspect for incorrect basic engine parts. Inspect camshaft, cylinder heads, pistons, etc.
Visually and physically check the vacuum hoses for splits, kinks, and proper connections and routing as shown on the underhood Vehicle Emission Control Information label.
Inspect transmission Torque Converter Clutch (TCC) operation. See appropriate DIAGNOSIS article in AUTOMATIC TRANSMISSIONS. The scan tool should indicate a RPM drop, when the system commands the TCC ON.
Inspect exhaust system for a possible restriction. Inspect exhaust system for damaged or collapsed pipes. Inspect the mufflers for heat distress or possible internal failure. Inspect for possible plugged catalytic converters.
Electromagnetic Interference (EMI) on the reference circuit can cause an engine miss condition. A scan tool can usually detect EMI by monitoring the engine RPM. A sudden increase in RPM with little change in actual engine RPM change indicates EMI is present. Inspect for high voltage components near ignition control circuits, if a condition exists.
Inspect the Park/Neutral Position (PNP) switch circuit.
Inspect brake system for dragging or improper operation. Verify that operator does not drive with a foot on the brake pedal.