GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 1998 🢒 GMC C-Series Medium Duty Truck B7 🢒 Engine 🢒 Engine Controls - 6.0L and 7.0L 🢒 Hard Start

Hard Start

Checks

Action

DEFINITION: The engine cranks OK but does not start for a long time. The engine does eventually run or may start but immediately dies.

Preliminary Checks
    • Refer to Symptoms for the Important Preliminary Checks.
    • Make sure the driver is using the correct starting procedure.

Sensor Checks
    • Check the Engine Coolant Temperature (ECT) sensor using the scan tool in order to compare the engine coolant temperature with the ambient air temperature on a cold engine. Check for a high resistance in the coolant sensor circuit or the sensor itself if the coolant temperature reading is more than 5°C (41°F) greater or less than the ambient air temperature on a cold engine. Refer to DTC 15 ECT Sensor Circuit High .
    • Check the Throttle Position (TP) sensor. If a sticking throttle shaft or a binding linkage causes a high TP sensor voltage (open throttle indication), the ECM will not control the idle. Monitoring the TP sensor voltage, the scan tool and/or voltmeter should display less than 1.25 volts with throttle closed. Refer to Fuel Metering System Diagnosis .

Fuel System Checks
    • Check the fuel pump relay for operation. The fuel pump should operate for 2 seconds when turning ON the ignition. Refer to Fuel Pump Electrical Circuit Diagnosis .
    • Check the fuel pressure. Refer to Fuel System Diagnosis .
    • Check for water contamination in the fuel.
    • Check the fuel pump check valve. A faulty in-tank fuel pump check valve will allow the fuel in the lines to drain back to the tank after stopping the engine. In order to check for this condition:
        1. Turn the ignition OFF.
        2. Disconnect the fuel line at the fuel filter.
        3. Remove the tank filler cap.
        4. Connect a radiator test pump to the fuel line and apply 102 kPa (15 psi) of pressure. If the pressure holds for 60 seconds, the check valve is OK.

Ignition System Checks
    • Check for the proper ignition voltage output with the spark tester J 26792 or equivalent.
    • Check the spark plugs for the following:
       - Wet plugs
       - Cracks
       - Wear
       - Improper gap
       - Burned electrodes
       - Heavy deposits
    • Check for bare and/or shorted ignition wires.
    • Check for moisture in the distributor cap.
    • Check for loose ignition coil connections.
    • Check for a worn distributor shaft.
    • Check the pickup coil and connections.
    • Check the Ignition Control circuit for an open or a short to ground. Refer to Distributor Ignition (DI) System Diagnosis .

Additional Check
    • Check the IAC operation. Refer to Fuel Metering System Diagnosis .
    • Check for no crank signal.
    • Check the EGR Valve operation. Refer to Exhaust Gas Recirculation (EGR) System Check .
    • Check the Service Bulletins for PROM updates.