Positive Crankcase Ventilation Valve: Description and Operation

Crank Case Vent System:

All engines produce small amounts of blow-by gases which seep past the piston rings and into the crankcase. These blow-by gases are the result of the high pressures developed within the combustion chamber during the combustion process, and contain undesirable pollutants. To prevent blow-by gases from entering the atmosphere while allowing proper crankcase ventilation, all engines use a PCV system.
The vent system used by the 1.6L does not depend on the flow of scavenging air, as do other Ford engines, but evacuates crank case vapors that are drawn into the intake manifold in metered amounts according to the manifold depression and the fixed orifice as they become available. If the availability is low (as at idle), air may be drawn in along with the vapors. If the availability is high (increased blow-by at high speeds) some vapors will be delivered to the intake manifold and any amount over that will go into the air cleaner. The fixed orifice is the critical point of the system.