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Home >> Mitsubishi >> 1989 >> Sigma Standard >> Repair and Diagnosis >> Engine Performance >> System >> Basic Testing >> Fuel Pressure >> Fuel Injected Engines >> Fuel Pressure
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Fuel Pressure

  1. On Montero, Sigma and Van/Wagon, disconnect fuel pump harness connector at fuel tank. On Starion, remove floor panel in luggage compartment. Disconnect electrical connector near fuel pump. On all models, start engine. Let engine run until it stops. Turn ignition off. Disconnect negative battery terminal. Connect fuel pump harness connector.
    CAUTION: Use a rag to cover fuel hose connection prior to loosening bolt as there may still be residual fuel pressure in system.
  2. On 1.6L and 2.0L (DOHC), remove brace for access to fuel line. On all engines, disconnect high pressure fuel hose at delivery pipe. See Figure . Connect hose Adapter (MD998742 ) (except Starion) and Adapter Hose (MD998709 ) (except Starion) to delivery pipe. On Starion, use Adapter (MD998700 ) for connection to injection mixer. On Montero, use Adapter (MD998700 ) and Adapter Hose (MD998753 ) for connection to delivery pipe. On all models, connect fuel hose to adapter. Connect a fuel pressure gauge to hose adapter.
    NOTE: On Sigma and Van/Wagon models, fuel hose adapter tool number is not available from manufacturer.
  3. Connect negative battery terminal. Connect battery voltage to fuel pump test terminal. Refer to FUEL PUMP TEST TERMINAL LOCATION  table. Ensure no fuel leaks are present.
  4. Start engine and idle. Measure fuel pressure with vacuum hose connected to fuel pressure regulator. Disconnect and plug vacuum hose from pressure regulator. Record fuel pressure readings. Refer to FUEL PRESSURE SPECIFICATIONS  table.
  5. Raise engine speed to 2500-3000 RPM, 2-3 times. Ensure fuel pressure does not drop when engine returns to idle. Check for fuel pressure in fuel return hose by gently pinching hose while raising engine speed.
  6. There will not be any fuel pressure in return hose if fuel volume is low. Turn engine off. If fuel pressure is lower than specification, check for a faulty fuel pressure regulator or fuel pump.
  7. 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 for regulator is connected or disconnected, check for a leaking vacuum hose.
  8. Fuel pressure should not drop off. If fuel pressure drops suddenly, check for leakage in fuel pump. If fuel pressure drops slowly, check for leakage at injector. Remove fuel pressure gauge. Install a new "O" ring at end of high pressure hose.
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