Inspection of the Natural Gas Fuel System, If Equipped

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  1. Inspect fuel tanks for dents, scratches, gouges, or other signs of damage. Inspect the fuel lines and connections for leaks.
    Check that the fuel tanks are securely mounted. Look for signs of abrasion between components.
    Compressed Natural Gas (CNG) Fuel System : Ensure that the CNG fuel cylinder storage box is secured to the frame. Inspect for signs of looseness.
    Liquefied Natural Gas (LNG) Fuel System : Ensure that the LNG fuel tank is secured to the mounting brackets and that the mounting brackets are secured to the frame. Ensure all rubber isolator straps are secure around the LNG fuel tank.
  2. Check for the presence of all required decals present in the following locations:

    • Gas detection system overhead console;

    • Above the door handle on both doors;

    • Left front bumper;

    • End-of-frame crossmember;

    • LNG fuel tank fill port (maximum psi), if equipped.

  3. Check for the presence of vent caps on pressure relief valves and devices. If any caps are missing, have the fuel system inspected by a qualified technician.
    CNG Fuel System : Each fuel cylinder should have two caps (one on each end), which are visible on the back of the CNG fuel cylinder storage box. One additional cap is located on the pressure relief valve on the inboard side of the CNG fuel box, next to the fuel outlet line.
    LNG Fuel System : A red cap should be present on the secondary relief valve (Fig.).

    1. Pressure Control Regulator

    2. Vapor Shutoff Valve

    3. Fuel Fill Hose

    4. Secondary Relief Valve (red cap)

    5. Fuel Fill Fitting

    6. Fuel Level Sender Box

    7. Primary Relief Valve

    8. Tank Pressure Gauge

    9. Fill Vent Fitting

    10. Excess Flow Valve

    11. Fuel Shutoff Valve (liquid)

    12. Fill Check Valve

    Fig. 1, LNG Tank Plumbing Components

  4. Inspect all plumbing components, including the fuel shutoff valve(s), primary and secondary relief valves, and the LNG vapor shutoff and excess flow valves, if equipped, for signs of damage or leaks. See Fig. or Fig..
    Inspect the fuel fill fitting for signs of damage or leaks.
    Inspect all lines for signs of leaks or damage, and check all threaded connections.

    1. High Pressure Gauge

    2. Low Pressure Gauge

    3. Manual Fuel Shutoff Valve

    4. Fuel Fill Port

    Fig. 2, CNG Fuel Panel

  5. Inspect all fuel gauge components for signs of leaks or damage. Inspect the fuel level sender cable and wiring.
  6. Inspect all coolant hoses for signs of chafing, kinks, or leaks. The LNG fuel system utilizes coolant hoses between the engine and the vaporizer; the CNG fuel system utilizes coolant hoses between the engine and the pressure regulator inside the fuel panel.
  7. If equipped with an LNG fuel system, check the fuel tank pressure gauge to ensure that pressure is within the normal range of 120 to 150 psi (827 to 1034 kPa). If tank pressure exceeds 230 psi (1586 kPa) and the pressure relief valve does not open automatically, vent the tank immediately.
  8. Inspect the LNG vaporizer for signs of damage or leaks. See Fig.. Inspect the vaporizer mounting brackets for signs of looseness.

    1. Pressure Relief Device

    2. Fuel Inlet Line

    3. Check Valve

    4. CNG Quick-Connect Port

    5. Coolant Inlet Line

    6. Vaporizer

    7. Fuel Shutoff Solenoid Valve

    8. Coolant Outlet Line

    9. Pressure Gauge

    10. Overpressure Regulator

    11. Pressure Relief Valve

    12. Fuel Outlet Line

    Fig. 3, LNG Vaporizer Assembly

Note:
Parent topic: Daily Pretrip Inspection and Maintenance
Document Number: 0000117335
Manual Publication Date: 2025-02-11
Topic Publication Date: 2024-05-09