Possible Causes & Corrections

Check the following items:

• Search for bulletins.
• Ensure vehicle operator is using the correct starting procedure.
• 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 for a restricted exhaust.
• Inspect the fuel pump relay for proper operation. The fuel pump should operate for the first 2 seconds after turning ignition on. Refer to Fuel Pump Electrical Circuit Diagnosis under FUEL SYSTEMS in BASIC DIAGNOSTIC PROCEDURES - 4.2L BRAVADA, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article.
• 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 fuel injector coil test. Refer to FUEL SYSTEMS in SYSTEM & COMPONENT TESTING - 4.2L BRAVADA, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article.
• Perform fuel injector balance test. Refer to FUEL SYSTEMS in SYSTEM & COMPONENT TESTING - 4.2L BRAVADA, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article.
• Inspect fuel pump check valve. Refer to FUEL SYSTEMS in BASIC DIAGNOSTIC PROCEDURES - 4.2L BRAVADA, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article.
• Inspect the spark plugs for wet plugs, cracks, wear, improper gap, burned electrodes or heavy deposits.
• Inspect for loose ignition coil connections
• Inspect for loose ignition control module connections.
• Inspect for a faulty control module or ignition system grounds.
• Improper valve timing.
• Low compression.
• Worn rocker arms.
• Broken or weak valve springs.
• Worn camshaft lobes.
• Proper Cam Phaser operation.
• Inspect for a restricted exhaust.