Subaru Coupes/Sedans/Wagons 1985-1996 Repair Guide

Crankcase Ventilation System



See Figures 1, 2, 3 and 4

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Fig. Fig. 1: PCV system-1.2L engine

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Fig. Fig. 2: PCV system-1.6L and 1.8L carbureted engines

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Fig. Fig. 3: PCV system-fuel injected engine

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Fig. Fig. 4: Cutaway view of a PCV valve

A Positive Crankcase Ventilation (PCV) system is used to help reduce emission of blow-by gasses into the atmosphere. The system consists of a sealed oil filler cap, rocker covers with an emission outlet and fresh air inlet, connecting hoses, PCV valve and air cleaner.

At part throttle, blow-by gas in the crankcase flows into the intake manifold through the PCV valve by the strong vacuum of the intake manifold. Under this condition, the fresh air is introduced into the crankcase through the rocker cover fresh air inlet.

At wide open throttle, a part of the blow-by gas flows into the air intake duct through the connecting hose and is drawn to the throttle chamber. The system uses this route because the reduced intake manifold vacuum is not able to draw the increased amount of blow-by gases generated by the wide open throttle condition through the PCV valve.


PCV Valve

See Figure 5

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Fig. Fig. 5: Check the PCV valve for vacuum at idle

The PCV valve should be checked at regular intervals and replaced as required. If the valve is found to be defective, do not clean, replace it. Connection and system hoses can be cleaned by using compressed air. Check all hoses for clogging, split or hardening condition. Replace as necessary.

  1. With the engine running, remove the valve from its mounting. A hissing sound should be heard and vacuum should be felt from the inlet side of the valve.
  3. Reinstall the valve. Remove the crankcase inlet air cleaner. Loosely hold a piece of stiff paper over the opening in the rocker cover. Allow one minute for the crankcase pressure to reduce. The paper should then be pulled against the rocker cover with noticeable force. Replace the inlet air cleaner in the rocker cover.
  5. With the engine stopped, remove the PCV valve and shake. A clicking sound should be heard indicating that the valve is not stuck.
  7. If the valve fails any of the above tests, it should be replaced.

Regulating Orifice System

Clean the hoses and calibrating orifice internally. Blow away foreign matter with compressed air. Check the hoses for cracks, fatigue and swelling. Replace if necessary.


  1. Label the PCV valve or regulating orifice hoses before removing.
  3. Disconnect the hoses and remove the valve/orifice.
  5. Connect the hoses to the new valve/orifice and install the valve/orifice.