Don't bother to take your MBC apart just yet. I am betting that there is nothing wrong with it at all. I think that it would be a waste of time. It was working before the boost leak test. So, it is still good.

Advice is very much like opinions, and we all know what opinions are similar to. But, I intend to give you some unsolicited advice anyway. For whatever it may be worth. You can choose to disregard it....Fine.

You'll probably ask yourselves where I am headed with this....But, way back when, I had a 1975 BMW 2002 factory turbo sedan. These relatively primitive, first generation turbocharged cars featured a non-wastegated boost control system. Instead of an exhaust wastegate, boost was limited to 8 PSI strictly via a compressor bypass valve. NO WASTEGATE!

Think of that compressor bypass valve(which was VTA, BTW) as being similar to the boost leak that your car had been suffering from just recently. The BMW's compressor bypass valve had an 8 PSI spring which vented charge air once pressure reached 8 PSI. Of course the turbine wheel kept spinning faster and faster....But what the hell?

Your boost leak was acting like my 2002 turbo's compressor bypass valve by venting charge air pressure. Furthermore, you had no preload on your gate so your flapper valve was lifting full open at only 11 PSI. Oh yeah and you also had the MBC muddying the picture as well as an uncrushed IX DV lifting at 13-17 PSI.

It has been my experience that MBC's do a much better job of controlling boost when their adjustability range is relatively narrow. For example if your WGA is preloaded to 18 PSI and peak boost is 24 PSI. Then your MBC only controls boost over a narrow 6 PSI range. By contrast, setup as you presently have yours, it has to "stretch" from 11 PSI to 24 PSI(13#).

Also, you should remember that now you have no more boost leakage whatsoever. That was fixed. In effect, imagine that you have sealed off the compressor bypass valve. Let's simplify, and forget about your MBC for a minute. Realize that your actuator is seeing much higher levels of intake manifold pressure which, this in turn, is moving the actuator's internal diaphragm much, much sooner than it had done previously. End result: Since your WGA is not preloaded whatsoever to counteract this higher intake charge pressure....Now your actuator is lifting the flapper valve full-open way sooner than it had before when you had the boost leak.

If you look at your turbocharger system in terms of the pressure differential between turbine inlet and compressor outlet, you have proportionally increased pressure on the cold side by sealing off your major boost leak(s). Any given intake manifold pressure is now being reached at a much lower exhaust pressure and shaft speed. This is lifting the flapper valve much sooner. Yours is not a MBC related problem. It is a WG preload issue.

My advice FWIW: Increase wastegate spring pressure up to 18-19 PSI from its current level of 11#. Then the MBC's range of functionality will fall back into line.

Side Note: I realize that this is even more OT. But that old 2002 turbo was a funny girl. She had what was basically a Bosch mechanical fuel injection system. There was the standard looking Bosch injection pump which was belt, gear, or chain driven(IDK, ?) as on the more pedestrian normally-aspirated 2002tii models but the back cover of the pump was modified by Bosch to receive signals from a pressure sensing bellows system which enriched the fuel delivery under positive boost conditions. Granted, it was a pretty cobby setup but it worked. The turbocharger was this archaic KKK twin scroll El Hugeo unit off a diesel truck application. Very slow spooling. We would seal off the compressor bypass valve and even so boost only reached 12 PSI by engine redline. But, yes this is another story totally. Sorry. Forgive me. LOL

 

It seems to have been fixed my mbc was reallllyyyyy dirty

 

That's good news! Maybe I'll go back and erase my misguided rant.

 

BUMP! You mean "fixed" in a relative sense, don't you? At least you can raise your boost level again. So, I guess that compared to the way it was when it was stuck unresponsively at 17#, it seems fixed.

But, your boost curve must suck. Turbocharger spool up has to suck. Midrange torque and overall responsiveness most definitely suck as well.

Anytime that you are controlling boost via a MBC and your WG spring pressure is down in the 10-12 PSI range, then things suck. If you are at all interested in quick turbocharger spool up then you must preload your WG up to at least 14 PSI as a very minimal setting. For 23-24 PSI peak boost level you should really be preloaded up around 17-19 PSI.

There is just no way that there is going to be anything at all happening at a measly 10-12 PSI of spring pressure. No way!

 

Isn't 11 psi preload stock?