Possible Causes & Corrections
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Check the following items:
- Verify that the powertrain control module (PCM) grounds are clean, tight, and in the proper locations.
- Search for bulletins.
- Monitor Engine Coolant Temperature (ECT) sensor with scan tool. Compare engine coolant temperature with the ambient air temperature on a cold engine. If coolant temperature reading is more than 5 degrees more or less than the ambient air temperature on a cold engine, check for high resistance in the coolant sensor circuit.
- Inspect Mass Airflow (MAF) sensor installation. A MAF sensor that is incorrectly installed may cause a hard start condition. The embossed arrows on MAF sensor indicate direction of intake air flow. The arrows must point toward engine. Install MAF sensor in proper direction.
- Inspect Camshaft Position (CMP) sensor for proper mounting and/or a bad connection. An extended crank occurs if PCM does not receive a CMP signal.
- Check fuel pump relay operation. See FUEL PUMP ELECTRICAL CIRCUIT DIAGNOSIS under FUEL SYSTEMS in BASIC DIAGNOSTIC PROCEDURES - 8.1L AVALANCHE, SIERRA, SILVERADO, SUBURBAN & YUKON XL article.
- A faulty in-tank fuel pump check valve allows fuel in the lines to drain back to the tank after the engine stops. See FUEL SYSTEM PRESSURE TEST under FUEL SYSTEMS in BASIC DIAGNOSTIC PROCEDURES - 8.1L AVALANCHE, SIERRA, SILVERADO, SUBURBAN & YUKON XL article.
- Verify that both fuel injector fuses are not open. An open fuel injector fuse causes four injectors and four ignition coils not to operate. Inspect the injector circuits and the ignition coil circuits for an intermittent short to ground. Replace the fuse.
- 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 four ignition coils and four fuel injectors not to operate. Inspect the ignition coil circuits and the fuel injector circuits for an intermittent short to ground.
- Inspect for proper ignition voltage output with a Spark Tester (J-26792).
- Remove spark plugs and inspect for correct heat range, wet plugs, cracks, wear, improper gap, burned electrodes or heavy deposits.
- Determine cause of the conditions before replacing spark plugs.
- Inspect for bare or shorted ignition wires.
- 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.
- Excessive oil in combustion chamber or leaking valve seals.
- Low cylinder compression. See CYLINDER COMPRESSION PRESSURE under MECHANICAL INSPECTION under PRELIMINARY INSPECTION & ADJUSTMENTS in BASIC DIAGNOSTIC PROCEDURES - 8.1L AVALANCHE, SIERRA, SILVERADO, SUBURBAN & YUKON XL article.
- Combustion chambers for excessive carbon buildup. Clean chambers using top engine cleaner.
- Incorrect basic engine parts. Inspect cylinder heads, camshafts, pistons, etc.