1990 Mitsubishi Precis RS, AutomaticFACTORY OEM SERVICE PROCEDURE

Fuel Pressure

  1. On all models Mirage, disconnect fuel pump harness connector at fuel tank. On Mirage, remove rear seat cushion to disconnect fuel pump harness connector.
  2. On all models, start engine. Let engine run until it stops. Turn ignition off. Disconnect negative battery terminal. Connect fuel pump harness connector. Use a rag to cover fuel hose connection prior to disconnecting high pressure fuel hose at fuel delivery pipe. Some residual fuel pressure may still be in system.
  3. On Galant 2.0L (DOHC), remove brace for access to high pressure fuel delivery pipe. On all engines, disconnect high pressure fuel hose at fuel delivery pipe.
  4. Connect fuel pressure gauge with adapter between fuel delivery pipe and high pressure hose. See Fig 1 . Connect negative battery terminal. Connect battery voltage to fuel pump test terminal. See FUEL PUMP TEST TERMINAL LOCATION  table. Ensure no fuel leaks are present. Disconnect battery voltage to fuel pump test terminal.
  5. Start engine and let idle. Measure fuel pressure with vacuum hose connected to fuel pressure regulator. Record fuel pressure reading. Disconnect and plug vacuum hose from fuel pressure regulator. Record fuel pressure reading. See REGULATED FUEL PRESSURE  table.
  6. Check for fuel pressure in fuel return hose by gently pinching hose while increasing engine speed. If fuel volume is low, fuel pressure in return hose will not be felt. Increase engine speed to 2500-3000 RPM, 2-3 times. Return engine to idle. Fuel pressure should not drop when engine is returned to idle.
  7. Turn engine off. On all models except Precis, ensure fuel pressure reading does not decrease within 2 minutes. On Precis, fuel pressure reading should not decrease within 5 minutes. If a decrease is noted, monitor speed of decrease.
  8. If fuel pressure is lower than specification, fuel pressure drops at idle after increasing engine speed to 2500-3000 RPM, or no fuel pressure in fuel return hose can be felt, check for clogged fuel filter, faulty fuel pressure regulator, or fuel pump.
  9. If fuel pressure is higher than specification, check for a faulty fuel pressure regulator or plugged fuel return line. If fuel pressure does not change when vacuum hose to regulator is connected or disconnected, check for a leaking or clogged vacuum hose to fuel pressure regulator or faulty fuel pressure regulator.
  10. If fuel pressure decreases suddenly after engine is stopped, check valve within fuel pump is not seated. Replace fuel pump. If fuel pressure drops slowly, fuel injector is leaking or fuel pressure regulator valve seat is leaking. Check for faulty fuel injector or fuel pressure regulator. Repair as required.
  11. When fuel pressure test is complete, reverse fuel pressure release procedure in steps 1) and 2) before disconnecting fuel pressure gauge. Install new "O" ring at end of high pressure hose. Check for fuel leaks.
    Fig 1: Typical Fuel Injected Engine Fuel Pressure Testing Connection
    G120113Courtesy of MITSUBISHI MOTOR SALES OF AMERICA.
    FUEL PUMP TEST TERMINAL LOCATION

    Application Wire Color Location
    Eclipse Black/White Left rear of battery compartment
    Galant Yellow/Green Left rear engine compartment
    Mirage 1.5L Black/White Center of firewall
    Mirage 1.6L Black/Blue Center of firewall
    Montero Black/White Behind right kick panel
    Pickup Black/Blue Left lower instrument panel
    Precis Yellow Left rear engine compartment
    Sigma Black/Blue Left rear engine compartmentt
    Van/Wagon Red/Green Left rear of battery compartment
    REGULATED FUEL PRESSURE

    Application At Idle w/Vacuum psi (kg/cm2 ) At Idle w/o Vacuum psi (kg/cm2 )
    Eclipse 1.8L & 2.0L (VIN R), Galant 2.0L (VIN R), Mirage, Pickup (2.4L), Precis, & Van/Wagon 38 (2.7) 47-50 (3.3-3.5)
    Eclipse 2.0L (VIN U) 27 (1.9) 36-38 (2.5-2.7)
    Galant 2.0L (VIN V), Montero (3.0L), Pickup (3.0L) & Sigma 38 (2.7) 47-53 (3.3-3.5)
Factory Service Tools

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When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

  • • You smell fuel, burning insulation, or see smoke.
  • • Brakes feel soft, pull hard to one side, or make grinding noises.
  • • The engine overheats, stalls repeatedly, or misfires under load.
  • • You are missing required tools, torque specs, or safe lifting equipment.
  • • You are not confident in the next step or safety outcome.