Update: I was able to successfully create a pressure tester after some trial and error. Details and photos below.
What you will need:
1. 3'' threaded PVC/ABS cap
2. Air compressor and male quick connect fitting and a pressure regulator
3. Duct tape / electrical tape / Teflon tape
4. Various size rubber plugs – I could not find these in store so I ordered these:
https://www.amazon.com/gp/product/B0...UTF8&psc=1
You will need to remove the intake as you will be pressurizing from the accordion part of the turbo inlet. Note, the 3'' cap will not fit/seal properly without modification. While you can force it into the intake tube and try to clamp it down, air will leak past the threads and it will pop out once you build pressure.
Start by drilling a hole in the center of the cap for the quick connect fitting and then just thread it in (I did not even tap the hole – I just drilled it out smaller than the thread size and forced the threads in; it didn't leak). Then, you will need to sand down the outer diameter from the 3'' cap, ideally with a taper so that you can easily slide it into the intake, as shown in the pictures below. The easiest way to achieve this is to connect a drill to the quick connect fitting. You really don't want to try and manually sand this down because (1) it will take forever, and (2) you risk creating low/high spots. You need to reduce the OD perfectly around the circumference or it will not seal. Once you get it connected to the drill, just hold sand paper around it while you spin with the drill. Once you have reduce the OD a bit (test by sliding it into the intake), you will need to add some sort of rubberized tape around the circumference so that it will seal once clamped into the intake tube. Teflon tape worked well for me, but it kindof made a mess (shredded) when I pulled the cap out. Electrical tape was OK, gorilla tape was the best.
Depending on how much you sanded down, wrap the tape around the circumference a few times until the cap is difficult but not impossible to get into the intake.
Make sure that you installed it PAST the first lip or it will definitely pop out once you start building pressure (had this happen several times at first). It need to be even with or slightly in further than the hose clamp area. Once it is secured you need to move on to plugging various points along the intake system that could leak/bleed air.
First, remove the PCV hose (from the valve cover, not from the intake) and cap with the appropriate size rubber plug. Surprisingly I didn't need to secure this beyond just pushing the plug in tight; it held ~15psi. See picture below. Next, remove the 8AT vaccum line from the charpe pipe (if you have it). Again, use the correct size rubber plug to plug that hole, or a vacuum cap if you have it (I didn't get one with my CP). For this plug, I put a zip tie around the CP to hold the plug in place because the fit was not as tight. See picture.
Finally, which may not be absolutely necessary, use a small plug to cap the other end of the 8AT vacuum line there it would go back into the intake. What I observed is that air seemed to come out of that hose even with the side that goes to the CP disconnected, at least for a few seconds. There seems to be some sort of valve that takes a second or two to switch closed – when you first start pressurizing the system, air comes out, but you can hear an audible change in sound and the air stop flowing after a few seconds. I assume this is how you don't have a permanent boost leak through the CP-8AT connection.
After you have all the plugs in and everything connected, start
slowly increasing pressure with your regulator. Remember it will take a few second to fill everything with air so don't go quickly or you could overshoot target PSI. Once you start building pressure in the system the gauge on the regulated size of your compressor will reflect that. I would start at only about 5psi and you will see if there are any obvious leaks. Increase to 15-20 psi (no reason go to over that if you are on stock turbo) and check for any smaller leaks. I used the soapy water in a spray bottle method but it wasn't even really necessary. There are only a few connection points and it is very obvious if one of them is leaking once you pressurize.
I wrote about my horrible experience with a boost leak at VRSF IC-CP connection and what I had to go through to get that to seal over on this thread:
https://f30.bimmerpost.com/forums/sh...6#post25393576
Pictures below