Bronco L6-300 4.9L VIN Y 1-bbl (1983)
Air Diverter Valve: Description and Operation
Air Bypass Valves
Fig. 64 Normally closed air bypass valves
Fig. 65 Normally open air bypass valves with vacuum vents
Fig. 66 Normally open air bypass valves without vacuum vent
There are two general groups of bypass valves, normally open and normally closed. Both groups are available in both remote and pump-mounted
versions.
Normally closed valves, Fig. 64, supply air to the exhaust system with medium and high applied vacuum signals during normal modes (engine
operating at normal operating temperature), short idles, and some accelerations. With low or no vacuum applied to pump, air is dumped through silencer
ports of valve.
Normally open valves with a vacuum vent, Fig. 65, provide a timed air dump during decelerations and also dump when a vacuum pressure difference
is maintained between the signal port and the vent port. The signal port must have 3 inches Hg more vacuum than the vent port to hold the dump. This
mode is used to protect the catalyst from overheating.
Normally open valves without a vacuum vent, Fig. 66, provide a timed dump of air for 1.1 or 2.8 seconds when a sudden high vacuum of about 20
