Fuel Pressure: Testing and Inspection

CAUTION: Check fuel system pressure only when fuel cylinders are half full or more.

1. Remove engine cover.
2. Remove air filter housing.

Fuel Injectors And Rail:

3. Remove the service port cap from fuel rail.

Fuel Pressure Gauge Attachment:

4. Attach a pressure gauge to the service port.
5. Start the engine and bring to operating temperature. Minimum fuel injector operating pressure is 90 psi. Maximum operating pressure is 140 psi.

Proper fuel system operating pressures will depend on:
- Regulated fuel cylinder pressure (at low-pressure side of fuel pressure regulator)
- Engine temperature
- Outside ambient temperature
- Condition of low-pressure fuel shut-off solenoid
- Condition of fuel injectors
- Condition of high-pressure fuel shut-off solenoid and solenoid relay
- Engine load requirements
6. If the operating pressure is above 140 psi, with the fuel cylinders half full or more, and the engine fully warmed up, replace the fuel pressure regulator.
7. If pressure is lower than 90 psi:
a) Be sure cylinders have fuel.
b) Be sure all 3 (or 4) fuel control valves are fully opened.
c) Be sure manual gas shut-off valve is opened (in horizontal position).
d) Be sure there are no kinks or bends in any of fuel tubes.
e) Refer to Low pressure fuel shut off solenoid testing.
Low Pressure Fuel Shut-Off Solenoid (CNG)

f) Refer to High-Pressure Fuel Shut-Off Solenoid Test.
High Pressure Fuel Shut-Off Solenoid (CNG)

g) Refer to fuel injector test.
Testing and Inspection

After tests and repairs have been completed:

8. Remove pressure test gauge.
9. Check system for leaks. Refer to Testing For Gas Leaks for procedures.
10. Install air filter housing.
11. Install engine cover.