GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2002 🢒 GMC K Sierra - 4WD (CNG) 🢒 Engine 🢒 Engine Controls - 6.0L 🢒 Poor Fuel Fill Quality

Checks

Action

DEFINITION 1: Fuel filling time, as measured against previous filling time, is noticeably longer than expected.

DEFINITION 2: Only one CNG fuel tank appears to fill.

Fuel System Checks

Inspect for the following conditions:

    • A contaminated or clogged fill valve filter. A service interval is not specified for the fill valve filter. Its condition depends on fuel quality. Use of CNG with excessive amounts of contaminants or compressor oil will increase the frequency of service. Service if necessary.
    • A fill line union check valve that is restricted or improperly installed. The check valve flow direction arrow should point towards the fuel tank.

       Important: The customer may comment that one fuel tank does not appear to fill. An inoperative high pressure lock-off (HPL) solenoid valve will allow a fuel tank to fill, but will not allow it to empty.

    • Test all of the high pressure lock-off (HPL) solenoids for proper operation. Test by performing the following:
        1. Disconnect the HPL solenoid power and ground connector at each CNG fuel tank except one.
        2. Operate the engine on CNG while only one HPL solenoid is connected.
        3. Observe the fuel gage while the engine is operating on one CNG fuel tank for about two minutes.
        4. Repeat the above procedure for each HPL until all CNG fuel tanks have independently operated the engine.
        5. An HPL condition exists if any of the following symptoms are observed:
   • The fuel gage drops toward empty.
   • The engine switches over to gasoline operation (KL6).
   • The engine stalls (KL8).
        6. If an HPL condition exists, test for the following:
   • A closed HPL manual shut-off valve.
   • A lack of power or ground at the HPL connector when commanded ON.
   • An open or shorted HPL solenoid. Replace the HPL as necessary. Refer to High Pressure Lock-Off Solenoid Replacement .