Trouble with WOT Boost control

[A//// Guy]

1991 GSX with 20G and Tial BOV and Tial 38mm external wastegate off the O2 housing, and a Joe P MBC.

Every time I get the car up to the 15PSI spring pressure of the external wastegate the car immediatly starts stuttering the boost up and down (goes to 15psi then stutters downward) The BOV is basically going nuts... If I dont go up to 15PSI everything works fine (bov and boost).

I dont think I have it setup correctly with the MBC or maybe I need to use 2 different hose sources instead of T-ing off both the BOV and wastegate on the same line?

Here is a diagram of how I have it connected now - The MBC shouldnt be controlling the boost because I have it set to the lowest it can go, and the Wastegate's spring is 15PSI- so that is what the cutoff should be.

Let me know what to do or how to hook it up, maybe my MBC is going bad or something....

TIA
Peter

[Shane@DBPerformance]

Judging by the drawing, you have the MBC hooked up backwards.

[Matt D.]

Originally Posted by ecoli

Judging by the drawing, you have the MBC hooked up backwards.

I agree.

[A//// Guy]

I do have it hooked up the other way around. The bottom port on the MBC goes to the BOV and the side port goes to the Wastegate. Just made the drawing off a little.

I have the instructions from the MBC and I hooked it up how it looks. But on the Wastegate install it shows to use the top port on the wastegate and I didnt because others told me to hook it up like I have in the diagram.

I unhooked the MBC all together tonight and have the line going straight to the BOV and to the Wastegate. That should open it at 15psi correct? Using the MBC it will just delay the wastegate even more if Im correct.

Here is how tials says to hook it up... Again I am just using the bottom port and leaving the top port oepen.
http://www.tialsport.com/images/WG_Install_Diagram.gif

Original Image edited to how I have it hooked up...

[Matt D.]

Ignore that drawing concerning how they have the lines going to the wastegate. Hook the line from the MBC to the bottom port on the wastegate and let the top one vent. Try it that way without the MBC and see what happens.

[A//// Guy]

Yea I hooked it up so the line from the IM goes righ to the T and then to the BOV and bottom wastegate port.

Maybe my MBC is plugged up or something.

[Matt D.]

Take the MBC apart and put it back together. Sometimes the ball and spring get hung up and won't open. Put it back together as loose as possible and then you will be running strictly off of the wastegate for boost control. From there adjust the MBC accordingly.

[A//// Guy]

Alright thanks guys for the help, Ill let you know what happens.