I have a 1.8t with a k04 bought from ebay. Have APR chip intended for a k03. Carbonio intake and godspeed FMIC. My n75 valve will not work alone. I have added a MBC to it. Full throttle without the MBC will put the car into limp mode. With MBC the n75 works under partial throttle. Mechanic at Gensis Racing Development said the reason of my overboost is because of faulty MBC. I replaced it with a grimmspeed. Still over boosts! Could this be a wastegate issue or an electrical issue? Also it will over boost with just the MBC even though the MBC is brand new. I am supposed to be boosting around 15-17 psi. It hits 20-25 psi but will not pull at all.

 

maybe get a k04 tune from APR? GIAC pc-16 file ( i think ). Its probably the current tune plus the MBC.

dont quote me though..

 

What type of MBC is it? And correct me if I'm wrong, but you are running the MBC and N75 at the same time? If so, how are they hooked up?

I've had to deal with overboosting where boost would exceed what my boost gauge could read, and it would only do it in 2nd gear. Anyways, this is the solution I used:
Over Boost Solution Kit

 

So, even if you turn the mbc down it won't release at all? If all the hoses are fine, and you're setting the mbc correctly then the wastegate was adjusted too high or not adjusted at all. You should always test when the wastegate opens before you install a new turbo. It could be set to anything, especially ebay turbos. My wastegate opens at 7psi, but the n75 or mbc controls when to release pressure.

Example:

If I set my mbc to release at 5psi, but the wastegate is set to 20 it won't release until 20psi. If my mbc is set to 20psi and wastegate is set to open at 2 psi it wont' open until 20. Get it?

If you want to check when the wg opens, just hook a compressor up to the nipple on the wastegate with a hose somehow. Turn the compressor all the way down, and slowly raise the psi on the compressor. If the wg doesn't open by 10-15 psi then it's set too high.

 

Stupidly enough APR does not have a k04 file for the b5 (Tiptronic anyways). GIAC does but at $950.
If I have the MBC by itself set to 15 psi without the N75 it boosts at 20-25psi depending on its mood... I am using A grimmspeed MBC. I have it parallel to the MBC according to Manual boost controller - S4wiki
If i use just the n75 like it should be. It will go into limp mode. No matter what I do it overboosts I now have my chip set to stock mode. It will hold at 7psi at around 1k-4k rpms then 4-6k rpms will hold at 10 psi. No matter which gear it is. But it will spike to 15 upon acceleration. Im going to post a video to youtube asap to show you guys what exactly i mean.
I really appreciate all the help! Talk to you soon.

 

The GIAC tune for K04 should only be $300 I thought... I paid $300 for my K03 flash, and then had my ECU re-flashed to GIAC PC-16 (their more aggressive K04-0015 tune). Granted the shop I use charges about $80-100 labor for each time the ECU is flashed, so all totalled I've spent ~$500 total so far.

And APR should have a K04 file, doesn't matter if you are tiptronic or manual. The ECU doesn't really care either way. HOWEVER, only GIAC makes a "tip chip" that flashes the tiptronic's control module to reduce the time between shifts (or something like that).

This seems rather strange. Are you sure your N75 is not faulty? And it doesn't seem like your MBC is working properly, unless it's your wastegate that isn't working properly. As shown in the link you posted with a MBC boost should hit a certain level and stay their; it shouldn't fluctuate. What type of MBC is the Grimmspeed? I've read that the bleeder-type of MBC is one of the better choices to use on our cars (like the BoostValve I linked to above).

EDIT: Another thought on the MBC: maybe the spring in yours is too soft to handle higher boost levels. The BoostValve MBC I use came with an extra, stiffer spring.

 

Sounds like either a wg issue or the wg reference line from the mBC/n75 has a leak.

 

Heres what the gauge looks like.
Boost issue - YouTube
The fluctuation in psi is under consistent throttle.
I called apr and they said theres no k04 file for my car i dont know why. My grimmspeed is the bleeder type. The n75 I bought last year from Audi it is the one with the H at the end of the item number. I stupidly havent checked the wg line. Will check and get back. I called the closest GIAC dealer to me and they quoted me $950 with half an hour of labor for $50. Maybe my n75 wires are f'd up? The stock n75 did not work when i first put the k04 in.

 

I'd have to agree with judeisnotobscure on this one, could be a boost leak issue or something along those lines. Do you have the means to perform a boost leak test?

 

I do not. Know where I can get a cheap air compressor?