Positive Crankcase Ventilation: Description and Operation

PCV System Operation:

The Positive Crankcase Ventilation (PCV) system is provided to prevent the blow-by-gas from being emitted into atmosphere and it operates as follows. When the vacuum in the intake manifold is low (throttle valve open), the PCV valve is wide open due to its spring force. Thus a large amount of the blow-by-gas is drawn into the intake manifold. On the other hand, when the vacuum in the manifold is high, the PCV valve opening is limited due to the high vacuum. Thus the amount of the blow-by-gas drawn into the intake manifold is small.

RESULTS OF INCORRECT OPERATION

A plugged valve or hose may cause:

^ Rough idle.
^ Stalling or slow idle speed.
^ Oil leaks.
^ Oil in air cleaner.
^ Sludge in engine.

A leaking valve or hose would cause:

^ Rough idle.
^ Stalling.
^ High idle speed.