Durango 4WD V8-5.9L VIN Z (1998)
Fuel Pressure: Testing and Inspection
Fuel Pressure Test - With Test Port
Fig 8 Fuel Pressure Test Port - Typical
WARNING: THE FUEL SYSTEM IS UNDER CONSTANT FUEL PRESSURE EVEN WITH THE ENGINE OFF. BEFORE
DISCONNECTING FUEL LINE AT FUEL RAIL, THIS PRESSURE MUST BE RELEASED. REFER TO THE FUEL SYSTEM PRESSURE
RELEASE PROCEDURE.
NOTE: Use this test in conjunction with the Fuel Pump Capacity Test and Fuel Pressure Leak Down Test found elsewhere.
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.
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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 rise to specification.
NOTE: The fuel pressure test port is used on certain engines only. The test port is located on the fuel rail near the throttle position sensor (Fig. 8).
A sealing cap is screwed onto the test port.
All fuel systems are equipped with a fuel tank module mounted, combination fuel filter/fuel pressure regulator.
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The fuel pressure regulator is not controlled by engine vacuum.
Procedure
1. Remove protective cap at fuel rail test port. Connect the 0-414 kPa (0-60 psi) fuel pressure gauge (from gauge set 5069) to test port pressure fitting
on fuel rail.
2. Start and warm engine and note pressure gauge reading. Fuel pressure should be 339 kPa +/- 34 kPa (49.2 psi +/- 5 psi) at idle.
3. If engine runs but pressure is below 44.2 psi, check for a kinked fuel supply line somewhere between fuel rail and fuel pump module. If line is not
kinked, replace fuel pump module assembly. Refer to Fuel Pump Module Removal/Installation.
4. If operating pressure is above 54.2 psi, electric fuel pump is OK, but fuel pressure regulator is defective.
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Replace fuel filter/fuel pressure regulator.
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Certain filter/regulators may be serviced separately and some require the replacement of the fuel pump module assembly Refer to Fuel Filter
/Fuel Pressure Regulator Removal/Installation for more information.
