Mitsubishi Pick-ups and Montero 1983-1995 Repair Guide

Electric Fuel Pump

Print

Mechanical fuel pumps are generally not capable of delivering the high pressures required for fuel injection. Because of alternating motion of the pump arm, the mechanical pump is prone to wear and failure. An electric motor, driving a rotary or vane-type pump, provides a constant speed and pressure in the fuel line.

REMOVAL & INSTALLATION



See Figures 1 and 2


WARNING
In almost every case, replacing the Mitsubishi electric fuel pump requires removal of the fuel tank. Please refer to the fuel tank removal and installation procedure at the end of this section.

  1. Lift or move aside the carpet in the rear cargo area.
  2.  
  3. Remove the oval cover plate from the access hole.
  4.  
  5. Disconnect the fuel pump harness connector at the rear of the fuel tank.
  6.  
  7. Start the engine, allowing it to run until it runs out of fuel. This relieves pressure within the fuel system.
  8.  
  9. Turn the ignition switch OFF and disconnect the negative battery cable.
  10.  
  11. Remove the fuel filler cap.
  12.  
  13. Drain the fuel from the fuel tank into suitable container(s), each with an airtight lid.
  14.  
  15. Carefully, and using two wrenches on the fittings, disconnect the high pressure fuel line and the main fuel line from the pump. Remove the high pressure fuel hose at the body-side main pipe connection, unfasten the pump-side connection. Wrap each joint in a rag before loosening; some pressure may remain within the system.
  16.  
  17. Remove the fuel pump retaining nuts and carefully remove the pump from the tank.
  18.  

The fuel pump may still contain liquid fuel. Drain it into a suitable container with an airtight lid before performing any tests or inspections.

To install:
  1. Carefully install the pump into the tank and install the 6 retaining nuts onto the studs. Tighten the nuts evenly and in a crisscross pattern to 12 ft. lbs. (16 Nm).
  2.  
  3. Reinstall the high pressure and supply line to the pump.
  4.  


WARNING
Take great care when connecting the threaded high pressure lines. Start the threads by hand, then, while holding the hose side to keep it from turning, tighten the flare nut to 27 ft. lbs. (37 Nm).

  1. Connect the pump wiring harness.
  2.  
  3. Connect the negative battery cable. Turn the ignition key to ON but do not start the engine. You should hear the pump running. Allow it to run for about 10 seconds to build line pressure, then start the engine.
  4.  
  5. After the engine has run smoothly for a minute or two, shut the ignition off and check the work area for any trace of leakage. Attend to any fuel leaks immediately, remembering that the system has repressurized and must be handled safely.
  6.  
  7. Reinstall the cover on the access hole and replace the carpet in the cargo area.
  8.  



Click image to see an enlarged view

Fig. Fig. 1: Components of the fuel pump and fuel tank



Click image to see an enlarged view

Fig. Fig. 2: Components of the fuel pump-all models similar

TESTING



When diagnosing engine problems, particularly a "no start" condition, the fuel pump function should be checked. Because of the difficulty in reaching the fuel pump connections, Mitsubishi automobiles have a conveniently located test connector under the hood. V6 Monteros have the connector taped to a wiring harness inside the right front kick panel, near the ECM and relays.

This connector bypasses all of the controls in the system (ignition switch, pump relay, etc.) and sends voltage directly to the pump. When power is applied to the pump you should be able to hear it running, although the in-tank pumps require you remove the fuel filler cap and listen at the filler.

To use the test connector, make certain the ignition is OFF . Great damage may be caused if the system is tested with the key on. Locate the test connector in the engine compartment (on later Monteros it is located under the right-hand side of the dashboard)-it is generally on a short lead out of a wiring harness and looks like a plug that isn't connected to anything. Once found, use a jumper wire to connect the test terminal to the positive battery terminal. Listen for the fuel pump; if it runs, you know the pump motor is good. While the pump is running, gently squeeze one of the fuel lines and confirm that the pump is delivering fuel pressure. If it does not run, the pump itself is most likely defective OR the connector to the pump is faulty.

When the pump is removed from the tank, it may be checked by applying battery voltage (+) to the connector and grounding the housing. Only run the pump for one or two seconds during this test; the pump can be damaged by running without liquid.


CAUTION
Make certain the pump has been drained of residual fuel and is free of fuel vapors. Connecting and removing the test leads will cause sparks which can ignite any vapor in the area.

Additionally, the pump motor may be checked with an ohmmeter. Some resistance should be seen on the meter scale. If the meter shows no motion (infinite), the motor has an internal fault and the pump must be replaced.

 
label.common.footer.alt.autozoneLogo