Mitsubishi Eclipse 1990-1998 Repair Guide

Crankcase Ventilation System



See Figures 1, 2, 3 and 4

All engines are equipped with the Positive Crankcase Ventilation (PCV) system. The PCV system vents crankcase gases into the engine air intake where they are burned with the fuel and air mixture. The PCV system keeps pollutants from being released into the atmosphere. It also helps to keep the engine oil clean, by ridding the crankcase of moisture and corrosive fumes. The PCV system consists of the PCV valve, the nipple in the air intake and the connecting hoses.

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Fig. Fig. 1: Typical PCV system airflow

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Fig. Fig. 2: The PCV valve can be found either threaded to the valve cover, ...

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Fig. Fig. 3: ... mounted in a grommet on the valve cover ...

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Fig. Fig. 4: ... or in the hose between the valve cover and intake plenum

Incorrect operation of the PCV system can cause multiple driveability symptoms.

A plugged valve or hose may cause:

Rough idle
Stalling or slow idle speed
Oil leaks
Sludge in engine

A leaking valve or hose would cause:

Rough idle
High idle speed


See Figures 5 and 6

  1. Disconnect the ventilation hose from the PCV valve. Remove the PCV valve from the engine. Once removed, reconnect the ventilation hose to the valve.
  3. Start the engine and allow to idle. Place a finger over open end of the PCV valve. Make sure intake manifold vacuum is felt on finger.
  5. If vacuum is not felt, the PCV valve may be restricted.

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Fig. Fig. 5: With the engine idling, check the end of the PCV valve to see if vacuum is present

  1. Turn the engine OFF and remove the PCV valve from the hose.
  3. Insert a thin stick into the threaded end of the PCV valve. Push on the inner plunger and inspect for movement.

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Fig. Fig. 6: Inspect the PCV valve for inner plunger movement. If the plunger is bound or sticking, replace the valve

  1. If plunger inside the PCV valve is not free to move back and forth, the valve is clogged and will require replacement.

It is possible to clean the valve using the appropriate solvent, but replacement is recommended.


For PCV valve removal and installation, please refer to General Information & Maintenance of this repair guide.