PCV System - Gasoline: Description

The positive crankcase ventilation system is designed to prevent contaminating hydrocarbons, created in the crankcase, from escaping into the atmosphere.

On all models other than Ford Motor Co. vehicles with 1.9L 2-bbl. engines, crankcase vapors are routed from the crankcase through a vacuum controlled ventilating valve (PCV) into the intake manifold. When vapors reach the intake manifold, they are mixed with air/fuel and burned in the combustion process.

On Ford Motor Co. vehicles with the 1.9L 2-Bbl. engine, the crankcase ventilation system is much different. All crankcase vapors that are drawn into the intake manifold are metered through a Dual Orifice valve assembly. A small orifice is connected to the intake manifold at all times. A larger orifice, controlled by a carburetor vacuum port signal, opens to the intake manifold during part throttle and wide open throttle operation. If the availability of crankcase vapor is low, air may be drawn along with crankcase vapor through the smaller orifice. If the availability of crankcase vapor is high, crankcase vapor is delivered to the intake manifold through both orifices. If the amount of crankcase vapor available exceeds that which can be handled by the 2 orifices, the excess flow is routed to the air cleaner.