hey every1,

So my boost used to be controlled by a home depot MBC, worked fine for a few months, then it stopped giving me 10psi...OK, so i threw that away and put in a Turbo XS MBC (the little blue one), tuned it and it held 10psi for a good year. Now this weekend im back at 10psi in the x-over pipe and 8psi at the UIM (typical 2psi pressure loss for the stock IC) and turning the adjustment screw does nothing. https://www.nopistons.com/forums/pub...1047683561.gif What could it be? The line from the y-pipe to the MBC to the wastegate actuator is good. The turbos have 30k miles on them, so i doubt it would be the actuator...but at the same time how could i "break" two MBC's in a year?



any help would be appreciated cuz im stumped.



-Zach

I generally have to adjust mine with the change in weather. Will it hold 10psi if you open it up a few turns?

turning it in/out even 4 or 5 complete turns yields no changes. I took off the intake and checked both lines (y-pipe > MBC > WG) and theyre fine with no kinks/holes/tears as well. https://www.nopistons.com/forums/pub...1047683561.gif

I have the same problem you are having, only i am sequential now. I can't go past 9psi, no matter how much i raise the boost on the profec :(

another weird thing...the TurboXS MBC has no ball and spring https://www.nopistons.com/forums/pub...1047683561.gif just a small air bleed screw.

Well the boost is either not being made, or it's being vented at some point. Any 'whooshing' sounds coming from the motor?

not an answer to your question, just a boost question in general.

could an exhaust leak hinder boost pressure? and how much?

well treceb, yes an exhaust leak could hinder boost pressure in only one way: if it was being leaked out before the turbine housing. For instance, the only way it could leak and affect your boost would be at the engine/exh manifold area. Any point past that and its already been forced to spin the turbine https://www.nopistons.com/forums/pub...IR#>/smile.png





No whoosing sounds newhere. Double checked that by putting a boost gauge on the x-over pipe AND the uim. Shows 10psi from the turbos, and 8psi at the UIM which from what ive gathered is the nominal 2psi drop from the stock IC.

https://www.nopistons.com/forums/pub...1047683664.gif Is the wastegate fully closing?

interesting that you bring that up. Ive noticed boost isnt building as fast either. https://www.nopistons.com/forums/pub..._DIR#>/sad.png Think its possible for a wastegate/ WG actuator to fail at 30k miles? https://www.nopistons.com/forums/pub...1047683358.gif