Positive Crankcase Ventilation (PCV Valve)
The (PCV) positive crankcase ventilation system removes blowby gases that bypass the piston rings during the ignition (power) stroke. It consists of a valve and a supporting hose, connected between the intake manifold and the cylinder valve cover. When the engine’s at idle, there is high vacuum and this vacuum holds the valve tight against its seat. This prevents the valve from allowing blowby gases into the intake. A stuck open PCV valve will result in a large vacuum leak and a rough idle. When the engine is accelerated, the manifold vacuum drops, allowing the valve to open. This allows the flow of crankcase gas or blowby to be ignited in the combustion process instead of released into the atmosphere.