Pickup Models
The air by-pass control system consists of a diaphragm and air control unit. When intake manifold vacuum by-passes the boost control system, it activates the diaphragm. The diaphragm opens the air control unit which supplies additional air into the intake manifold.
The amount of air entering the manifold is controlled by servo-action of the air control unit and vacuum control unit. Manifold vacuum can be kept very close to the pre-determined value during deceleration by this tightly controlled circuit.