Checking Fuel Pressure:
Use this test in conjunction with the Fuel Pump Pressure Test and Fuel Pump Capacity Test.

Check Valve Operation:
The electric fuel pump outlet contains a one-way check valve to prevent fuel flow back into the tank and to maintain fuel supply line pressure (engine warm) when the pump is not operational. It is also used to keep the fuel supply line full of gasoline the when pump is not operational. After the vehicle has cooled down, fuel pressure may drop to 0 psi (cold fluid contracts), but liquid gasoline will remain in the fuel supply line between the check valve and fuel injectors. Fuel pressure that has dropped to 0 psi on a cooled down vehicle (engine OFF) is a normal condition. When the electric fuel pump is activated, fuel pressure should immediately (1-2 seconds) rise to specification.

Abnormally long periods of cranking to restart a hot engine that has been shut down for a short period of time may be caused by:

• Fuel pressure bleeding past a fuel injector(s).
• Fuel pressure bleeding past the check valve in the fuel pump module.
• A defective fuel filter/pressure regulator.

Fuel Line Pressure Test Adapter Hose Tools may be required for the following tests.

1. Release fuel system pressure. Refer to the Fuel Pressure Release Procedure for your vehicle. Generally removing the fuel pump fuse and cranking the engine.

Fuel Line Identification:
The fuel pressure regulator is generally located on the fuel rail. On Chrysler products it is located on the top of the fuel pump/sending unit and is part of the fuel filter. Or it is located in front of the fuel tank and above the rear axle. Generally the fuel pressure regulator is equipped with three fuel line fittings, two at one end and one at the other end. One fitting is the supply line to the fuel rail. The other two fittings are connected to the fuel tank. Of these two fittings; one is used for fuel return to the fuel tank. The other fitting is a pressure line.

1. Using the correct Fuel Line Pressure Test Adapter connect the fuel pressure gauge to the test port on the fuel rail. If the fuel rail does not have a test port, the fuel pressure gauge gets teed in between the fuel filter and fuel rail.
2. Start engine and bring to normal operating temperature.
3. Observe fuel pressure test. Normal operating pressure should be about 49.2 psi ±5 psi for most vehicles. Check the service manual for you vehicle for the proper pressure.
4. Shut engine OFF.
5. Pressure should not fall below 0 psi for five minutes.
6. If pressure falls below 30 psi, it must be determined if a fuel injector, the supply check valve within the fuel pump module, the fuel pressure regulator, or a fuel line is leaking.
7. Again, start engine and bring to normal operating temperature.
8. Shut engine OFF.
9. Testing for fuel injector or fuel rail leakage: Clamp off the return line. If pressure falls below 30 psi, a fuel injector or the fuel rail is leaking. If pressure holds, it is a bad fuel pump check valve.

Testing For Fuel Pressure Regulator Leakage:
If the fuel pressure regulator can not be isolated from, or is part of, the fuel rail, both will have to be replaced.

As always, check the service manual for the proper procedures and specifications for your particular vehicle.