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Home >> Eagle >> 1990 >> Summit LX, 1.5 X, Standard >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Basic Testing >> Fuel Pressure >> Fuel Injected Engines >> Fuel Pressure

Fuel Pressure

  1. On all models except Colt & Summit disconnect fuel pump harness connector at fuel tank. On Colt, 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. 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  . 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  .
  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. Ensure fuel pressure reading does not decrease within 2 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
Colt, Colt 200 & Summit Black/White Center of firewall
Colt Vista N/A Right of center on firewall
Colt Wagon Red Near left shock tower
Ram-50 Black/Blue Left lower inst. panel
REGULATED FUEL PRESSURE

Application At Idle w/ Vacuum psi (kg/cm2 ) At Idle w/o Vacuum psi (kg/cm2 )
All Models 38 (2.7) 47-50 (3.3-3.5)
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