Fuel Pressure Release: Service and Repair
Fuel Pressure RelievingWARNING: Compressed natural gas is flammable and highly explosive. You could be killed or seriously injured if leaking natural gas is ignited.
Stop the engine, and keep heat, sparks and flames away.
This procedure should be done outside in a well-ventilated area or in a properly equipped CNG shop.
Between the engine and the manual shut-off valve
This procedure will allow you to safely work on any part of the fuel system downstream of the manual shut-off valve, such as the fuel pressure regulator P1/P2 or the fuel injectors.
1. Close the manual shut-off valve (A).
2. Start the engine, and let it idle. After a few minutes, the engine will stall.
3. Turn the ignition switch OFF.
Between the fuel tank and the manual shutoff valve
This procedure will allow you to safely work on any part of the fuel system upstream of the manual shut-off valve, such as the fuel tank or fuel joint block.
1. Relieve the fuel pressure between the engine and the manual shut-off valve (see the procedure).
2. Disconnect the negative cable from the battery.
3. Disconnect the fuel supply pipe from the fuel pressure regulator P1. Be careful not the lose the O-rings.
4. Connect the vent tube to the fuel supply pipe.
5. Open the manual shut-off valve slowly.
Between the fuel receptacle and the fuel tank
This procedure will allow you to safety work on any part of the fuel system between the fuel joint block and fuel receptacle.
1. Relieve the fuel pressure between the fuel tank and the manual shut-off valve (see the previous procedure).
2. Loose the sealing bolt on the fuel joint block slowly.
3. Turn the fuel stem assembly 1/2-1 turn counterclockwise.
4. Replace the fuel stem assembly and sealing bolt O-ring.
At the fuel tank
NOTE: This procedure degrades the integrity of the fuel tank. If you do it, you will need to install a new tank.
1. Close the manual shut-off valve.
2. Start the engine, and let it idle. After a few minutes, the engine will stall.
3. Turn the ignition switch OFF, and disconnect the negative cable from the battery.
4. Connect a ground wire (A) (available from AH special tools department) to the fuel line to eliminate any static electricity.
5. Disconnect the fuel supply pipe (B) from the fuel pressure regulator P1 (C). Be careful not the lose the O-rings.
6. Connect the vent tube to the fuel supply pipe.
7. Secure the other end of the vent tube to the highest possible location.
8. Remove the fuel pipe duct, and slowly remove the manual lock-down valve (A). Install the manual override vent tool (B) (available from AH special tools department) in its place.
9. Slowly turn the tool's Allen bolt clockwise until it stops. This opens the line between the fuel tank and the manual shut-off valve.
10. Open the manual shut-off valve so fuel can vent from the fuel tank. The fuel tank is empty when the hissing sound goes away.
11. Remove the manual override vent tool (B).