Chrysler Full-Size Trucks 1989-1996 Repair Guide

Electric Fuel Pump

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CAUTION
The fuel injection system is under a constant pressure. Before servicing any part of the fuel injection system, the system pressure must be released. Use a clean shop towel to catch any fuel spray and take precautions to avoid the risk of fire.

The MFI system uses an electric fuel pump mounted in the fuel tank. The fuel pump used in this system is a positive displacement, roller vane immersible pump with a permanent magnet electric motor.

For 1992-93 3.9L and 5.2L models, the fuel is drawn in through an in-tank filter unit and pushed through the electric motor to the outlet. The pump contains two check valves. One valve is used to relieve internal fuel pump pressure and regulate maximum pump output. The other check valve, located near the pump outlet, restricts fuel movement in either direction when the pump is not operational. Voltage to operate the pump is supplied through the Auto Shutdown (ASD) relay.

For 1993-96 5.9L and 1994-96 3.9L/5.2L/8.0L models, as well as 1996 2.5L models with the "returnless'' fuel injection system, the fuel pump is referred to as the "fuel pump module''. For the returnless system, the fuel is drawn in through an opening tube in the bottom of a filter/regulator. The regulator portion is calibrated to maintain a fuel pressure of approximately 35-45 psi (241-310 kPa). The internal fuel filter is built into the assembly. The filter/regulator contains a diaphragm, calibrated springs and a fuel return valve. An internal check valve maintains some fuel pressure when the engine is not running to enable a satisfactory start-up. The internal diaphragm routes fuel in excess of 45 psi (310 kPa) back to the fuel tank. With this system, proper fuel pressure is controlled at the source, so there is no need for a separate return line from the engine to the tank as found in conventional fuel systems.

REMOVAL & INSTALLATION



1992-93 3.9L/5.2L Models
  1. Perform the fuel pressure release procedure described previously in this section.
  2.  
  3. Properly relieve the fuel system pressure and disconnect the negative battery cable.
  4.  
  5. Remove the fuel tank from the truck.
  6.  
  7. Remove the locking ring, then lift out the fuel pump module. Tag any lines for replacement.
  8.  
  9. Remove the sending unit attaching screws from the mounting bracket located on the drain tube.
  10.  
  11. Disconnect the wires from the sending unit, then remove the sending unit.
  12.  
  13. Remove the drain tube from the mounting lug at the bottom of the reservoir.
  14.  
  15. Remove the lower-most coil of the drain tube from the mounting lugs on top of the reservoir. Be careful to avoid unsnapping the return line check valve cover from the bottom of the reservoir.
  16.  
  17. Release the pump mounting bracket from the reservoir. Press the bracket with both thumbs toward the center of the reservoir.
  18.  
  19. Remove the pump mounting bracket and rubber collar from the hose. Cut the hose clamp on the supply line and discard the clamp. Remove the pump/filter assembly. Pry the filter from the pump.
  20.  

To install:
  1. Press a new filter onto the pump.
  2.  
  3. Using a new clamp, attach the supply hose.
  4.  
  5. Position the pump mounting bracket and rubber collar on the supply hose between the bulge in the hose and the pump.
  6.  
  7. Position the pump in the reservoir so that the filter aligns with the cavity in the reservoir.
  8.  
  9. Snap the pump bracket into the reservoir.
  10.  
  11. Position the coil tube on the reservoir so that the drain tube aligns with the mounting lugs on the reservoir.
  12.  
  13. Snap the lowermost coil into the mounting lugs on top of the reservoir.
  14.  
  15. Snap the drain tube into the lugs on the bottom of the reservoir.
  16.  
  17. Connect the wires to the sending unit.
  18.  
  19. Align the index tab on the level unit with the index hole in the mounting bracket.
  20.  
  21. Install the level unit screws.
  22.  
  23. Install the assembly in the tank.
  24.  

1993-96 5.9L, 1994-96 3.9L/5.2L/8.0L and 1996 2.5L Models
  1. Perform the fuel pressure release procedure described previously in this section.
  2.  
  3. Properly relieve the fuel system pressure and disconnect the negative battery cable.
  4.  
  5. Remove the fuel tank from the truck.
  6.  
  7. Note the direction of the fuel filter/fuel pressure regulator, the pressure relief/rollover valve and the pump electrical connector. These should all be pointed to the driver's side. Tag any lines for replacement, if necessary.
  8.  
  9. Remove the locknut threaded into the fuel tank. The fuel pump module will spring up when the locknut is removed.
  10.  
  11. Remove the module from the fuel tank.
  12.  

To install:
  1. Use a new gasket and position the fuel pump module in the opening. The fuel filter/fuel pressure regulator, the pressure relief/rollover valve and the fuel pump electrical connector should all be pointed to the driver's side of the vehicle when this unit is properly installed.
  2.  
  3. Position a new locknut over the top of the fuel pump module, then tighten the locknut.
  4.  
  5. Install the fuel tank.
  6.  

TESTING



The fuel system test port is located on the fuel rail in the engine bay.

1992-93 3.9L/5.2L Models

See Figures 1, 2 and 3



Click image to see an enlarged view

Fig. Fig. 1: Fuel pressure test port199296 3.9L engine



Click image to see an enlarged view

Fig. Fig. 2: Fuel pressure test port199296 5.2L engine



Click image to see an enlarged view

Fig. Fig. 3: A common fuel pressure test using a screw-ingauge rated to at least 60 psi (414 kPa)


CAUTION
Fuel system pressure must be released as previously described each time a fuel hose is to be disconnected. Take precautions to avoid the risk of fire.

  1. Remove the fuel intake hose from the throttle body and connect fuel system pressure testers C-3292, and C-4749, or equivalent, between the fuel filter hose and the throttle body.
  2.  
  3. Start the engine and read the gauge. Pressure should be 14.5 psi (100 kPa).
  4.  

Mopar® ATM tester C-4805 or equivalent can be used. With the ignition in the RUN position, depress the ATM button. This activates the fuel pump and pressurizes the system.

  1. If the fuel pressure is below specifications:
    1. Install the tester between the fuel filter hose and the fuel line.
    2.  
    3. Start the engine. If the pressure is now correct, replace the fuel filter. If no change is observed, gently squeeze the return hose. If the pressure increases, replace the pressure regulator. If no change is observed, the problem is either a plugged pump filter sock or a defective fuel pump.
    4.  

  2.  
  3. If the pressure is above specifications:
    1. Remove the fuel return hose from the throttle body. Connect a substitute hose and place the other end of the hose in a clean container.
    2.  
    3. Start the engine. If the pressure is now correct, check for a restricted fuel return line. If no change is observed, replace the fuel regulator.
    4.  

  4.  

1993-96 5.9L, 1994-96 3.9L/5.2L/8.0L and 1996 2.5L Models

See Figures 1, 2 and 3 (above)

With the engine at idle, the system fuel pressure should be within 35-45 psi (241-310 kPa).

  1. Uncap the pressure test port and screw in a fuel pressure gauge designed to read 0-60 psi (0-414 kPa), such as from set No. 5069. On the 8.0L engine, the test port is found at the front of the engine.
  2.  
  3. Read the gauge. If within specifications, it will show 35-45 psi (241-310 kPa).
  4.  
  5. If the pressure is 0 psi/kPa, you will need more extensive diagnosis using a DRBII or equivalent scan tool, and the appropriate Powertrain Diagnostics Procedures service manual. If the pressure is above 45 psi (310 kPa), the fuel pump is okay. Replace the fuel filter/fuel pressure regulator assembly.
  6.  

 
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