Positive Crankcase Ventilation: Description and Operation

This system recirculates emissions from the crankcase to the intake system. During periods of high intake manifold vacuum, crankcase vapors are drawn into the intake manifold from the top of the valve cover, through a restrictor. When the intake manifold vacuum is low (high load, full throttle) the crankcase vapors are drawn, unrestricted, into the air filter housing. The crankcase vapors are then drawn into the engine and burned.