Positive Crankcase Ventilation: Description and Operation

Fig. 11 Typical Positive Crankcase Ventilation (PCV) System:

POSITIVE CRANKCASE EMISSION CONTROL SYSTEM OPERATION

A closed ventilation system is used to prevent the escape of blow-by vapors to the atmosphere. The crankcase is ventilated using fresh air from the air cleaner. Fresh air is then mixed with blow-by vapors in the crankcase and the mixture is vented to the intake manifold through the PCV valve.

Operation Of The PCV System:

POSITIVE CRANKCASE VENTILATION (PCV) VALVE OPERATION

The PCV valve includes a metered orifice which limits the flow of crankcase vapors into the intake manifold as determined by intake manifold vacuum. Flow capacity is adequate for normal driving conditions. However, under heavy acceleration or during high speed driving manifold vacuum may be too low for complete scavenging of the blow-by gases. Under these conditions the crankcase vapors will backup into the air cleaner via the breather hose.