Inspecting the CNG Fuel System

p3 mm 47.06.000

Warning: As with all pressure vessels, CNG/LNG storage and fuel delivery systems are inherently dangerous and should be treated as such. Beyond the visual inspections listed below, all maintenance and repairs to compressed natural gas (CNG) or liquified natural gas (LNG) systems should be performed by trained personnel. Individuals who are not trained in all aspects concerning CNG/ LNG fuel delivery systems are not permitted to service, maintain, test, or inspect a system in any way. Failure to comply with safety regulations may lead to fire or explosion, resulting in property damage, personal injury, or death.

Notice: Do not use a high-pressure washer or steam cleaner on natural gas fuel system plumbing components, as this can introduce moisture and contaminants into the threads of the fittings and damage the sealants. It can also harm the integrity of the CNG tank, and can cause premature failure of the pressure relief devices (PRDs) causing loss of CNG.

Gas detection sensors are located on the cab overhead console, the sleeper, and in the engine compartment on the frontwall. The sensors are located in high areas, where rising gas vapors will pass by or accumulate. Do not use a high-pressure washer, steam cleaner, or silicone-based chemicals on the gas detection sensors, as this may permanently disable the sensors. When cleaning the vehicle, cover the sensors with a plastic covering. Keep the sensors covered until the area has been cleared of any cleaning fumes. Harsh chemicals and extremely high temperatures may damage the sensor.

Important: Use an approved NG leak checking solution while preforming the following inspection.

For Fuel Managements System inspections refer to the suppliers procedures and best practices. These below should be competed in accordance with FMS inspections.

  1. Ensure that the fuel cylinder storage box is secured to the frame. Inspect for any signs of looseness. If necessary, tighten the storage box mounting bolts 160 lbf·ft (217 N·m). See Fig..
    If necessary, tighten frame-rail-mounted tank mounting nuts and bolts as follows. See Fig..

    • Tank mounting bracket to frame rail nuts and bolts, 130 lbf·ft (176 N·m)

    • Top plate bolts, 160 lbf·ft (217 N·m)

    • Gusset bolts, 160 lbf·ft (217 N·m)

    1. Frame Rail

    2. CNG Fuel Cylinder Storage Box

    3. Mounting Bolts (qty 12 per side)

    Fig. 1, Fuel Cylinder Storage Box Mounting Bracket (passenger side shown)

    1. CNG Fuel Cylinder, Frame Rail Mounted

    2. Top Plate Bolts (qty 6 per side)

    3. Frame Rail

    4. Mounting Bracket

    5. Gussett Bolts (qty 2 per side)

    6. Bracket to Frame Nuts and Bolts (qty 8 per side)

    Fig. 2, Fuel Cylinder Mounting Bracket (frame-rail mounted tank)

    2. Note: During initial pre-delivery inspection (PDI), tighten the storage box mounting bolts (shown in Fig.) 180 lbf·ft (244 N·m).

  2. Inspect the fuel fill port for signs of damage, oil residue, or leaks. Ensure the port dust cover and the O-ring inside the port are both present and in good condition. See Fig. and Fig..

    1. High Pressure Gauge

    2. Low Pressure Gauge

    3. Manual Fuel Shutoff Valve

    4. Fuel Fill Ports and Dust Caps

    Fig. 3, CNG Fuel Panel (back-of-cab box only)

    1. High Pressure Gauge

    2. Tank Information

    3. Manual Fuel Shutoff Valve

    4. Fuel Fill Port and Dust Cap

    Fig. 4, CNG Fuel Panel (frame-rail mounted tank)

  3. Ensure that caps are present on all pressure relief devices.
  4. Check the following components for signs of damage or leaks.

    • Manual fuel shutoff valve

    • Coolant hoses and fittings

    • Fuel lines and fittings along the frame rails to the low pressure filters and going in to the engine

    • All fittings, connections, and joints

  5. Replace leaking or damaged fuel lines. Repair or replace leaking or damaged fittings.
Note:
Parent topic: Fuel
Document Number: 0000116613
Manual Publication Date: 2024-05-15
Topic Publication Date: 2024-11-22