1978-79 Fiesta

The crankcase ventilation system is controlled by a combination oil filler cap and crankcase control orifice and valves. These are all combined into the filler cap assembly. See Figure. Fresh air is drawn in from the air cleaner through the top connector on the filler cap.

It then flows through valve "D" and into the crankcase (through the bottom connector). After mixing with blow-by gases, it is then drawn up into the rocker cover and into the center connector. With no fresh air ventilation, blow-by gases close one-way valve "D". This reverse pressure opens valve "E", allowing blow-by to the dirty side of the air cleaner where gases are taken back into the induction system.