GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2007 🢒 Sierra Classic - 4WD 🢒 Engine 🢒 Engine Controls and Fuel - 8.1L 🢒 Hard Start

Inspection/Test

Action

DEFINITION: Engine cranks OK, but does not start for a long time. Does eventually run, or may start but immediately dies.

Preliminary
    • Refer to Important Preliminary Inspections Before Starting in Symptoms - Engine Controls .
    • Verify that the powertrain control module (PCM) grounds are clean, tight, and in the proper locations. Refer to Power and Grounding Component Views and Engine Controls Schematics .
    • Search for bulletins.

Sensor/System
    • Verify that the engine coolant temperature (ECT) sensor is not shifted in value. Connect a scan tool. Compare the engine coolant temperature to the intake air temperature (IAT) on a cold engine. The ECT and IAT sensor values should be within ± 3°C (5°F) of each other. If the ECT sensor is out of range with the IAT sensor, measure the resistance of the ECT sensor. Refer to Temperature Versus Resistance for resistance specifications.

       Important:  The embossed arrows on the MAF sensor indicate the direction of the intake air flow. The arrows must point toward the engine.

    • Inspect the mass air flow (MAF) sensor installation. A MAF sensor that is incorrectly installed may cause a hard start. Install the MAF in the proper direction. Refer to Mass Airflow Sensor/Intake Air Temperature Sensor Replacement .
    • Inspect the camshaft position (CMP) sensor for proper mounting and/or a bad connection. An extended crank occurs if the PCM does not receive a CMP signal.

Fuel System
    • Inspect the fuel pump relay operation. The fuel pump should turn ON for 2 seconds when you turn ON the ignition. Refer to Fuel Pump Electrical Circuit Diagnosis .
    • A faulty in-tank fuel pump check valve allows the fuel in the lines to drain back to the tank after the engine stops. Refer to Fuel System Diagnosis .
    • 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. Refer to Circuit Testing .
    • Inspect for incorrect fuel pressure. Refer to Fuel System Diagnosis .
    • Inspect for a contaminated fuel condition. Refer to Alcohol/Contaminants-in-Fuel Diagnosis .

Ignition System
    • 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. Refer to Circuit Testing . Replace the fuse.
    • Inspect for proper ignition voltage output with the J 26792 Spark Tester. Refer to Electronic Ignition (EI) System Diagnosis .
    • Remove the spark plugs and inspect for the following conditions:
       - Correct heat range
       - Wet plugs
       - Cracks
       - Wear
       - Improper gap
       - Burned electrodes
       - Heavy deposits
       - Refer to Spark Plug Inspection .
    • Determine the cause of the conditions before replacing the spark plugs.
    • Inspect for bare or shorted ignition wires. Refer to Spark Plug Wire Inspection .
    • Inspect for loose ignition coil grounds. Refer to Electronic Ignition (EI) System Diagnosis .

Engine Mechanical

Inspect for the following conditions:

    • Excessive oil in combustion chamber or leaking valve seals.
    • Low cylinder compression .
    • Combustion chambers for excessive carbon buildup--Clean the chambers using top engine cleaner. Follow the instructions on the can.
    • Incorrect basic or worn engine parts--Inspect the following:
       - Cylinder heads
       - Camshaft
       - Pistons, etc.