Inspection of the CNG Fuel System

sd mm 47.06.001

Warning: Natural gas is highly flammable. See the safety precautions listed in Safety Precautions of the Driver's Manual or of the Workshop Manual. Failure to observe these precautions could lead to the ignition of the natural gas, which could cause severe bodily injury, death, or property damage.

The following inspections must be performed by a qualified technician, in accordance with the manufacturer's established inspection criteria.

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.

Gas detection sensors are located on the cab overhead console 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.

Use a bubble solution to check for leaks while performing the following inspection.

  1. Inspect the fuel cylinders for dents or other signs of damage.

    Replace any leaking fuel cylinders.

  2. Ensure that the fuel cylinders are secured within the fuel cylinder storage box.
  3. 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..

    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)

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

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

    1. High Pressure Gauge

    2. Low Pressure Gauge

    3. Manual Fuel Shutoff Valve

    4. Fuel Fill Port and Dust Cap

    Fig. 2, CNG Fuel Panel

  5. nspect the pressure gauges on the fuel box for cracks. Ensure the indicator needles are present and in working condition. Inspect the gauge faces for accuracy and legibility.
  6. Ensure blue caps are present on all pressure relief devices. Each fuel cylinder is equipped with two caps (one on each end), which are visible on the back of the CNG fuel cylinder storage box. One cap is located on the pressure relief valve on the inboard side of the CNG fuel box, next to the fuel outlet line. Check the primary relief valve on the inboard side of the CNG fuel box for signs of damage or leaks.
  7. Check the following components for signs of damage or leaks:

    • manual fuel shutoff valve

    • fuel cylinder shutoff valves (see Fig.)

    • coolant hoses and fittings

    • fuel lines and fittings

    • all fittings, connections, and joints

  8. Replace leaking or damaged fuel lines. Repair or replace leaking or damaged fittings.

    1. Fuel Cylinder Storage Box

    2. Fuel Cylinder Shutoff Valves (qty 5)

    3. High-Pressure Gauge

    4. Low-Pressure Gauge

    5. Fuel Fill Port

    6. Dust Cap

    7. Manual Shutoff Valve

    8. Fuel Panel Access Door

    Fig. 3, CNG Fuel Cylinder Storage Box (5-cylinder system shown)

Note:
Parent topic: Fuel
Document Number: 0000120394
Manual Publication Date: 2024-05-23
Topic Publication Date: 2024-11-06