Tools Required

J 45878 Combustible Gas Detector

Caution: Natural gas is highly flammable. In order to reduce the risk of fire and personal injury, keep sparks, flames, and smoking materials away from the vehicle while you perform the Compressed Natural Gas (CNG) fuel system service.

Caution: The Compressed Natural Gas (CNG) system operates at pressures up to 24820 kpa (3600 psi). Relieve the CNG fuel system pressure before servicing CNG fuel system components in order to reduce the risk of fire and personal injury.

1. Relieve the fuel system pressure. Refer to Fuel Pressure Relief .

Caution: Unless directed otherwise, the ignition and start switch must be in the OFF or LOCK position, and all electrical loads must be OFF before servicing any electrical component. Disconnect the negative battery cable to prevent an electrical spark should a tool or equipment come in contact with an exposed electrical terminal. Failure to follow these precautions may result in personal injury and/or damage to the vehicle or its components.

2. Disconnect the negative battery cable. Refer to Battery Negative Cable Disconnection and Connection in Engine Electrical in the C/K Pickup Service Manual.



3. Remove the tank cover (2). Refer to Fuel Tank Cover Replacement .



4. Partially drain the coolant or pinch off the high pressure regulator (HPR) coolant hoses (3, 5). Refer to Cooling System Draining and Filling in Engine Cooling in the C/K Pickup Service Manual.
5. Loosen the hose clamps enough to move the clamps (2, 6) away from the HPR coolant fittings.
6. Disconnect the HPR coolant hoses (3, 5) from the HPR.
7. Disconnect the HPR fuel inlet line (9).
8. Disconnect the HPR fuel outlet line (4).
9. Remove the HPR fuel inlet line fitting from the HPR. Capture the filter spring, filter and seal that are located behind the fuel inlet line fitting.

Important: Do not hold the HPR using the HPR cover hex flange. As required, wedge a wrench between the HPR and the tank frame in order to keep the HPR from spinning in the bracket.

10. Remove the HPR mounting nut (1).
11. Remove the HPR from the mounting bracket.

Use the following procedure if any HPR fittings require replacement:

1. Remove the coolant fittings (2, 5).
2. Remove the pressure relief device (3).
3. Remove the fuel outlet fitting (4).



4. Remove the filter spring (4).
5. Remove the filter (3).
6. Remove the seal (2).

1. Install the filter seal (2).
2. Install the filter (3).
3. Install the filter spring (4).




Important: Prior to installation, apply pipe thread sealant with Teflon® to the threads of the following:

•	Fuel outlet fitting (4)

•	Pressure relief device (3)

•	Coolant fittings (2, 5)

4. Install the fuel outlet fitting (4).

Tighten
Tighten the fuel outlet fitting hand tight plus one to three turns as required to seal and properly align the fitting.

5. Install the pressure relief device (3).

Tighten
Tighten the pressure relief device hand tight plus one to three turns as required to seal the fitting.

6. Install the coolant fittings (2, 5).

Tighten
Tighten the coolant fittings hand tight plus one to three turns as required to seal and properly align the fitting.

1. Install the HPR assembly (8) to the mounting frame (7).

Notice: Use the correct fastener in the correct location. Replacement fasteners must be the correct part number for that application. Fasteners requiring replacement or fasteners requiring the use of thread locking compound or sealant are identified in the service procedure. Do not use paints, lubricants, or corrosion inhibitors on fasteners or fastener joint surfaces unless specified. These coatings affect fastener torque and joint clamping force and may damage the fastener. Use the correct tightening sequence and specifications when installing fasteners in order to avoid damage to parts and systems.

Important: Do not hold the HPR using the HPR cover hex flange. As required, wedge a wrench between the HPR and the tank frame in order to keep the HPR from spinning in the bracket.

2. Install the HPR mounting nut (1).

Tighten
Tighten the nut to 54 N·m (40 lb ft).

Caution: Natural gas is stored under high pressure. If a leak occurs, the high pressure could cause a personal injury. In order to prevent Compressed Natural Gas (CNG) fuel leaks, always replace the CNG fuel system O-rings during service.

3. Connect the HPR fuel outlet line (4) using a new O-ring face seal. Lubricate the O-ring with petroleum jelly.

Tighten
Tighten the fuel line to 37 N·m (27 lb ft).

Important: Prior to installing the fuel inlet line fitting confirm that the fuel filter, spring and seal are properly seated in the HPR.

4. Install the fuel inlet line fitting using a new O-ring. Lubricate the O-ring with petroleum jelly.

Tighten
Tighten the fuel line fitting to 48 N·m (35 lb ft).

5. Connect the HPR fuel inlet line (9) to the HPR fitting.

Tighten
Tighten the fuel line to 37 N·m (27 lb ft).

6. Connect the HPR coolant hoses (3, 5) to the HPR.
7. Tighten the coolant hose clamp (6) ensuring that the clamp fastens the hose to the HPR fitting.
8. Remove the coolant hose pinch pliers if used.

Caution: Unless directed otherwise, the ignition and start switch must be in the OFF or LOCK position, and all electrical loads must be OFF before servicing any electrical component. Disconnect the negative battery cable to prevent an electrical spark should a tool or equipment come in contact with an exposed electrical terminal. Failure to follow these precautions may result in personal injury and/or damage to the vehicle or its components.

9. Install the negative battery cable. Refer to Battery Negative Cable Disconnection and Connection in Engine Electrical in the C/K Pickup Service Manual.
10. Fill the cooling system. Refer to Cooling System Draining and Filling in Engine Cooling in the C/K Pickup Service Manual.
11. Inspect the cooling system for leaks. Refer to Loss of Coolant in Engine Cooling in the C/K Pickup Service Manual.
12. Start the vehicle and inspect for CNG fuel leaks at the serviced fitting using the J 45878 or an equivalent liquid leak detector.



13. Install the tank cover (2). Refer to Fuel Tank Cover Replacement .