Fuel Pressure Release: Service and Repair

The fuel system must be purged of natural gas prior to removing or repairing any fuel system component. The fuel tube purge procedure should be used if fuel cylinders or control valves are not to be serviced; however, if these are to be serviced, then fuel cylinder purge procedure should be used. To prevent accumulation of fumes, perform purge procedures outdoors.

FUEL TUBE PURGE

Fig. 2 CNG Manual Shutoff Valve Open Position:

1. On all cylinders, close fuel control valves by turning clockwise, then open manual shutoff valve, Fig. 2.
2. If engine will run, start and run until residual fuel is consumed and engine stalls, then attempt three more engine starts.
3. If servicing manual shut off valve or fuel gauge pressure transducer, proceed as follows:
a. Slowly loosen fuel tube fitting at inlet side of fuel pressure regulator until pressure begins to release.
b. Allow pressure to decrease gradually by loosening fitting in increments until all pressure is released.

4. If servicing fuel filter, fuel pressure regulator or high pressure solenoid, proceed as follows:
a. Slowly loosen fuel tube fittings at inlet and outlet sides of fuel pressure regulator until pressure begins to release.
b. Allow pressure to decrease gradually by loosening fitting in increments until all pressure is released.

5. If servicing fuel fill receptacle or one-way check valve, proceed as follows:

Fig. 3 CNG One-Way Check Valve & Fuel Tube Fittings:

a. Slowly loosen fuel tube fitting at outlet side of check valve, Fig. 3, until pressure begins to release.
b. Allow pressure to decrease gradually by loosening fitting in increments until all pressure is released.

6. If servicing low pressure fuel shutoff solenoid, fuel rail, fuel hose between fuel rail and solenoid, fuel pressure sensor or fuel temperature sensor, proceed as follows:
a. Slowly loosen fuel tube fitting at inlet side of low pressure fuel shutoff solenoid very slowly.
b. When pressure release begins, allow pressure to decrease gradually by loosening fitting in increments until all pressure is released.

7. Perform repairs to system as necessary, noting the following:
a. Although fuel tubes have been purged of natural gas, fuel cylinders remain under high pressure. Do not open cylinder valves until all high pressure components have be reconnected and sealed.

8. After repairs have been completed and all fuel system components are in place, use a suitable Go-No-Go inspection tool to inspect fuel system high pressure fittings.

FUEL CYLINDER PURGE

Fig. 2 CNG Manual Shutoff Valve Open Position:

1. Open manual shutoff valve, Fig. 2, then open fuel control valves on cylinders being serviced by turning clockwise. Ensure valves on cylinders not being serviced are fully closed.
2. If engine will run, start and run until all residual fuel is consumed, then attempt three more engine starts.
3. Slowly loosen fuel tube fitting at fuel control valve of cylinder being serviced; allow pressure to decrease gradually by loosening fitting in increments until all pressure is released.
4. Perform repairs to system as necessary, noting the following:
a. Although fuel tubes and opened fuel cylinders have been purged of natural gas, fuel cylinders not being serviced remain under high pressure. Do not open cylinder valves until all high pressure components have be reconnected and sealed.
b. After repairs have been completed and all fuel system components are in place, use a suitable Go-No-Go inspection tool to inspect fuel system high pressure fittings.