Positive Crankcase Ventilation

The PCV system consists of the PCV (Positive Crankcase Ventilation) valve, grommet, tube, and an air supply hose to the crankcase. Check around these fittings for any signs of oil. Everything must be tight. Oil leakage indicates a problem with the system.

PCV valve system.

When the engine is shut down or when there's a drop in intake manifold vacuum, a light spring holds the valve in its open position. The open PCV valve results in maximum crankcase ventilation. When the engine is at idle, high intake manifold vacuum pulls the valve upward, blocking the port to the intake manifold.

PCV Valve Symptoms

Symptoms of a faulty PCV Valve.

A stuck closed PCV valve results in excessive crankcase pressure. This excessive pressure causes oil to leak past seals and gaskets. A stuck open PCV valve or leaking hose results in a large vacuum leak, a rough idle and drivability issues like surging. A closed or tarnished PCV valve can cause engine oil to back up into the breather.

PCV Valve Testing

A PCV valve should rattle when shaken. If the valve doesn't rattle, it should be replaced. At idle, with the PCV valve removed from the valve cover, there should be engine vacuum at the PCV valve inlet.