Positive Crankcase Ventilation: Description and Operation

EMISSION CONTROL SYSTEM





EMISSION CONTROL INFORMATION LABEL
The Emission Control Information Label is located on the underside of the hood.
The label contains important emission specifications and setting procedures, as well as a vacuum hoses schematic with emission components identified.
When servicing the engine or emission systems, the Emission Control Information Label should be checked for up-to-date information.





POSITIVE CRANKCASE VENTILATION (PCV) SYSTEM
The term "blow-by gas" stands for the compressed gas and exploded gas which blow through cylinder-to-piston clearance, which contain a large amount of unburned gases such as CO and HC. The PCV (Positive Crankcase Ventilation) 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.