PCV Valve

Most crankcase ventilation systems use a PCV valve. It is basically a one-way check valve, held closed by spring pressure when engine is not running. This prevents hydrocarbon fumes from collecting in intake manifold which can result in hard starting.

When engine is running, manifold vacuum pulls PCV valve open allowing crankcase fumes to enter intake manifold. If engine backfires through intake manifold, PCV valve closes and stops any flow of gases. This prevents ignition of fumes in crankcase.

The PCV valve is usually located in a valve cover, intake manifold or in-line. To check, idle engine and place finger over PCV valve hose connection. If vacuum is not felt, PCV valve is defective. Generally, if PCV valve operation is questionable, replacement is recommended.