Escort L4-116 1.9L VIN 9 TBI (1987)
Positive Crankcase Ventilation: Description and Operation
PCV System
PURPOSE
This vent system does not depend on a flow of scavenging air, as do all other Ford engines. It evacuates crankcase vapors that are drawn into the
intake manifold in metered amounts through a Dual Orifice Valve Assembly.
OPERATION
A small orifice is connected to the intake manifold at all times. A larger orifice, controlled by a throttle body port signal, opens to the intake
manifold during part throttle and WOT operation.
If the availability of crankcase vapor is low (at idle for instance) air may be drawn along with crankcase vapor through the smaller orifice.
If the availability of crankcase vapor is high (at high speed operation) 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 two orifices, the excess flow is routed to the air cleaner. The
Dual Orifice Valve is the critical point of this system.