Not your average N75 issue. Please Help!

[MHobart17]

So I just bought my 01 A4 Quattro 1.8t a couple days ago, five speed, familiar with cars plenty but new to VW/Audi. Hooking up to Vag this week, which Im sure will be a whole new story, anyway.. Engine itself runs great, has a front mount, BOV, Cold air intake, boost guage, (PCV, Diverter and SAI delete), looks like they were doing alright building it but under the intake i found the awesome mess of a half ass attempt at what appears to be trying to run an MBC parallel with the N75. So on to my issue, the have one line coming off of the MBC going to a T that connects with one line that comes off the side of the N75, those to connect at that T and run to wastegate. The other side of the MBC is just open, no hose run to it. The N75 also has one line coming off the bottom with fitting that looks like it should connect to something, but is just chillin there, not connected to anything. Third side of the N75 is just also open, no hose or anything. Been looking at diagrams and know that its definitely not what should be going on there lol. Now how its acting... from take off, all through first, turbo really wont spool, maybe 2 psi at most, shift to 2nd,(2nd and third act about the same) it will spool up to between 5-10 psi at about 3500RPM then cut out and drop back down while still WOT, if I let off and put the pedal back down, it will kind of surge boost between 5-15psi and do its own thing and will go up to about 4500RPM, so from my understanding, not going into limp mode, and have always shifted in that area because I dont wanna blow her up not knowing whats going on in there. Just curious if anybody had any Ideas, would like to cut out MBC and go back to just N75 but need to know where these lines hook up, or at least even to finish the parallel set up. Not sure what goes where, I will post some pics soon.

[offroader1006]

Ok,

I'm going to ignore the last half with the driveability concern and just focus on getting the n75 plumbed properly.


Your n75 should have a long port, and a two short ports.

The long one is for the ambient air(in the turbo inlet pipe). The one OPPOSITE of the long one is the Wastegate actuator. The one pointing perpendicular is the turbo pressure(on the turbo housing).

Here's a diagram.




For parallel, you just use two T's and run the mbc per the manufacturers instructions, just to the T's for the respective spot.

Here's a diagram for that.




I would try just the n75 first to remove as many failure points as possible, then go from there.

Do this, and see how the boost acts.