Is my Compressor broken or not???

I have the same problem 2008 INT PROSTAR ISX450. Changed air compressor, air dryer 2 times and 4 governors. No one knows whats wrong.
After reading this post i checked exhaust port and it had plastic plug in it. after removing it and a test drive its doing the same thing. Should it be capped? I just don't know what

 

No i have 1996 international 9200

 

Noit should nt, but Some times specialy the factory reset ones come with a plug just to protect exhaust port so dirt won't stick in it and plugged. If you look at it real close u will c it. It is two peace and air comes out freely while dirt can't get in

 

I just looked at this plug and like you said, two peace and air comes out freely. Truck goes back to the shop Friday. Mechanic said he got 2 more things to check.

 

Meho did you solve problems with compressor ?