Legacy Outback Limited AWD F4-2.5L DOHC (1998)
Positive Crankcase Ventilation Valve: Description and Operation
Positive Crankcase Ventilation System
PURPOSE
The Positive Crankcase Ventilation System prevents air pollution caused by blow-by gasses being vented to the atmosphere.
The valve is threaded into the intake manifold.
OPERATION
At part throttle, blow-by gas and filtered air from the filter in the air cleaner are drawn by strong vacuum into the intake manifold through a
connecting hose and PCV valve. At wide open throttle, part of the blow-by gas flows into the air cleaner through a connecting hose and is then
drawn into the engine through the throttle valve. This compensates for lowered manifold vacuum at high engine speeds.