Inspection of the Natural Gas Fuel System, If Equipped

m2 dm 11.05.004
  1. Leak test all fuel system components, joints, and fittings using a methane detector. A bubble solution can be used to pinpoint the exact location of leaks.
    Replace any leaking or damaged fuel tanks and fuel lines; repair or replace leaking or damaged fittings.
  2. Drain the CNG high-pressure fuel filter housing, if equipped.
    1. Purge the CNG fuel lines by closing the CNG fuel cylinder shutoff valves. Start the engine and let it idle until the fuel lines are empty and the engine stops.
      Gauges on the fuel panel should now read at or near 0 psi (0 kPa).
    2. Close the manual fuel shutoff valve on the fuel panel.
    3. Remove the two capscrews that secure the access cover to the fuel panel, then remove the access cover. See Fig.. Save the capscrews for installation.

      1. Fuel Panel Access Cover

      2. Capscrews (qty 2)

      3. Wiring Harness

      4. Pressure Relief Valve and Cap

      5. Coolant Outlet Line

      6. Coolant Inlet Line

      7. Fuel Inlet Line (to fuel cylinders)

      8. Fuel Outlet Line (to engine)

      Fig. 1, CNG Fuel Panel Assembly

    4. Slowly open the bleed valve on the manifold to relieve remaining fuel pressure within the system. See Fig..

      1. Coolant Inlet Port

      2. Coolant Outlet Port

      3. Pressure Relief Valve

      4. Pressure Regulator

      5. Wiring Harness

      6. Manifold Bleed Valve

      7. Manifold

      8. Manual Fuel Shutoff Valve

      9. Fuel Fill Port

      10. High-Pressure Filter

      11. Filter Bowl

      12. Filter Drain Plug

      13. Solenoid Valve

      14. Fuel Line To Cylinders

      Fig. 2, CNG Fuel Panel Components

    5. Put a clean receptacle under the filter assembly.

      6. Important: Some pressure may remain in the fuel system between the solenoid valve and the engine. Use caution when loosening fittings, as a small amount of gas may leak out.

    6. Using an 11/16-inch wrench, remove the drain plug from the filter bowl.
      When all liquid has drained, install and tighten the drain plug on the filter bowl.
    7. Close the bleed valve on the manifold and open the manual fuel shutoff valve on the fuel panel.
      Open the fuel cylinder shutoff valves.
    8. Use a methane detector to leak test all fuel system components between the fuel cylinders and the solenoid valve. A bubble solution can be used to pinpoint the exact location of leaks.
      Repair or replace any leaking components.
    9. Install the access cover on the fuel panel.
Note:
Parent topic: Monthly Post-Trip Inspection and Maintenance
Document Number: 0000117330
Manual Publication Date: 2025-02-11
Topic Publication Date: 2024-05-09