Grand Cherokee 2WD V8-4.7L VIN N (2000)
Fuel Pressure: Testing and Inspection
Fuel Pressure Leak Down Test
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 pump is not operational. It is also used to keep the fuel supply line full of gasoline 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 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:
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Fuel pressure bleeding past a fuel injector(s).
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Fuel pressure bleeding past the check valve in the fuel pump module.
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A defective fuel filter/pressure regulator.
Two # 6539, 5/16", Fuel Line Pressure Test Adapter Hose Tools are required for the following tests.
1. Release fuel system pressure. Refer to Fuel Pressure Release Procedure.
2. Raise vehicle.
Fig. 11 Disconnect Fuel Pressure Line At Filter/Regulator
Fuel Line Identification: The fuel filter/pressure regulator is located in front of the fuel tank and above the rear axle. It is transversely mounted to a
chassis crossmember (left-to-right). The filter/regulator is equipped with 3 fuel line fittings (2 at one end and 1 at the other end). The single fitting
facing the left side of the vehicle is the supply line to the fuel rail (Fig. 11). The 2 fittings facing the right side of the vehicle are connected to the
fuel tank,Of these 2 fittings, the fitting towards the front is used for fuel return to the fuel tank. The fitting towards the rear is a pressure line. This
rear fitting must be disconnected for the following step.
3. See previous step. Disconnect fuel pressure line at rear of filter/regulator. This is a 5/16" quick-connect fitting (Fig. 11). Refer to Quick-Connect
Fittings for procedures.
4. Obtain correct Fuel Line Pressure Test Adapter Hose Tool # 6539 for 5/16" fuel lines. Connect one end of this Special Tool into the disconnected
fuel pressure line. Connect the other end of the Tool into fitting on filter/regulator.
