Positive Crankcase Ventilation: Description and Operation

PURPOSE
Crankcase emission controls prevent crankcase gases from escaping into the atmosphere. Instead, the gases are routed to the intake manifold where they are ignited in the combustion process.

OPERATION
When the engine is at idle or under light load, intake manifold vacuum creates a vacuum in the crankcase through the PCV hose. Fresh air is supplied to the PVC system by the air cleaner and hose. As fresh air passes through the air cleaner, impurities are prevented from entering the engine.

When vacuum in the crankcase is less then that in the air cleaner, which occurs at full load and/or with large air-flow quantities, no fresh air is supplied. Instead, the flow in the connection between the valve cover and the air cleaner reverses and the crankcase gases pass both ways. In this way, the PCV system can deal with relatively large quantities of crankcase gases without any entering the atmosphere.