Description & Operation
Vehicles use a closed dual return type crankcase ventilation system. This consists of a PCV valve, a hose connecting the valve cover with the PCV valve, and a breather hose connecting the air cleaner with the valve cover.
When intake manifold vacuum is high, the PCV valve draws blow-by gases from the valve cover into the intake manifold for burning. When intake manifold vacuum is low (during wide open throttle), blow-by gases flow from the valve cover into the air cleaner where they mix with intake air.