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.

A light spring holds the valve in the open position when the engine is off or when there’s a drop in manifold vacuum. This results in maximum crankcase ventilation. When the engine is at idle, high manifold vacuum pulls the valve upward blocking the port to the intake manifold. Spring pressure verses vacuum pressure.

A stuck closed PCV valve will cause excessive crankcase pressure. This excessive pressure results in leaking oil seals and gaskets. A stuck open valve or leaking PCV hose will cause drivability issues like surging. A closed or tarnished PCV valve will cause oil to back up into the breather. A PCV valve should rattle when shaken. If the valve doesn't rattle, it must be replaced. At idle, with the PCV valve removed from the valve cover, there should be vacuum at the PCV valve inlet.