During Acceleration, High Speed, or Heavy Load

When the engine is accelerated, operated at high speed, or under heavy load, the manifold vacuum is less than it would be at idle or during deceleration. During acceleration, the PCV valve spring force is stronger than the vacuum pull from the intake manifold. This forces the valve toward the crankcase end of the valve housing. With the valve in this position, more crankcase vapors can flow into the intake manifold because the flow path offers less restriction. This larger flow path offsets the fact that the manifold vacuum is less during these operating conditions.