Whats this part?

[Mark Jones]

Does anyone what the part in the red circle is, what is does and where the vacuum line is connected? Oh course, when I got my Mustang, it was not connected. I see in the parts catalogs that it is very expensive to replace.
I don't know whether to hook it up or remove it and weld a block plate in its place.

 

[Hemikiller]

That's the vacuum motor for the auxiliary air inlet door. The line is connected to a manifold vacuum source. There are several schemas used depending upon the emissions controls fitted. Mustang Barn has the vacuum diagrams on their website.

https://mustangbarn.com/technical-information/

 

[Mark Jones]

Thank You Hemikiller. I will check out Mustang Barn. Also thanks for the diagram. It answered a few other questions for me too.

 

[Doug's 73 Mach1]

At idle vacuum to actuator pulls the door closed letting the snorkel be the only air inlet to the air cleaner. When accelerating intake manifold vacuum is not as strong and the actuator internal spring pushes the door open letting air also come into the air cleaner along with the snorkel air. This lets the carburetor draw air in a little easier for better performance. Ram air works the same way, the vacuum actuated flappers open when the intake manifold vacuum is less strong.

 

[Spike Morelli]

NPD lists that Vacuum Motor Assembly, complete, as part #9D612-8A, brand new.

 

[Mark Jones]

At idle vacuum to actuator pulls the door closed letting the snorkel be the only air inlet to the air cleaner. When accelerating intake manifold vacuum is not as strong and the actuator internal spring pushes the door open letting air also come into the air cleaner along with the snorkel air. This lets the carburetor draw air in a little easier for better performance. Ram air works the same way, the vacuum actuated flappers open when the intake manifold vacuum is less strong.

Thanks for the info Doug. I wondered why the door was open. Makes sense now. I will test operation with a vacuum pump and see if it still works. I hate to have to buy another one as they are very expensive.

 

[Mark Jones]

NPD lists that Vacuum Motor Assembly, complete, as part #9D612-8A, brand new.

Thanks for the info Spike. I am hoping mine still works so I dont have to purchase one.