What the hell is this? And Why?
 

so i have the car started, up on jacks looking for my exaust leak. i found it.
on the pipe below the Y there is a stem with threads. a big stem like for your air conditioner. there is no cap and hot loud air coming from it. what ever goes ther, i need. but what is it. and why?

It is right by the O2 sensor?

If so then it's for a test pipe. You will need to just cap it off. If you dont see the O2 sensor, then it's missing and that's where it goes.

Do you mean #22 or #21 on this diagram? http://www.pelicanparts.com/PartsLookup/HTML/944_USA_82_85_KATALOG/202-05-Frame3.htm

number 21 is it. interesting. i have never noticed one on any other style car.
ok, anyone have one laying around? thanks for that link. i was having a hard time finding that.

ya, that's a test port to hook up and test the exhaust.

I have never seen the actual test tube. but any place that does exhaust work, or even any shop that has a welder can do this. It's just a typical exhaust bung cap.

thanks for the info. i just ran down to midas and they capped it off with a weld for $10.00
So far that was the best $10 i spent on the car. Sounds 1000% better.

There is an official part number for the cap that goes on that fitting. It's $28 !!

The P-car mechanic that did the clutch job on my car just cut the tube sticking out, bent it over and crimped it. He said a TSB instructed him to do that or cap it. Seems that the tube never got hot enough to prevent acidic condensation from corroding the tube.