I apologize if this has been covered before, but my search options were limited as the search function excluded the most important key words I was using.

I have Revo software, my N75 valve throws codes, and I'm over boosting at 27 psi. So I'm assuming it's a no brainer to start with replacement of the N75 valve. I plan on a big turbo build in the future, so a boost controller is a given. My question is if I could eliminate the N75 and N249 valves and just use a MBC in their place? From what I gathered on google and some other 1.8t forums this seems to be an acceptable mod. I understand that they leave the electrical connector in place for the N75 valve, but how to bypass and install everything else is somewhat of a mystery to me. Is there a DIY article anywhere for this?

 

I'm running the diode mod on a stock AWM with a Forge MBC and a foot of vac line looped on the N75 and it works fine.

 

To start, the N249 is totally separate from controlling boost, it simply controls how/when boost is released by the DV. Many people whose cars come with a N249 run a vacuum line straight from the DV to the intake manifold and then leave the N249 plugged in.

You could replace the N75 with a MBC but many people prefer the smoothness of using the N75 over a MBC. What you are experiencing with that 27psi boost spike can be eliminated by running a MBC in parallel with the N75. This way you still get the smooth boost control of the N75, but the MBC (when set properly) will limit the peak boost to whichever level you set (so if you set the MBC to allow boost up to 20psi, it will limit boost to 20psi).

Here is a diagram showing this procedure to restrict overboosting:
Over Boost Solution Kit

 

I like the idea of the diode mod, I'd have done that if the previous owner hadn't already installed Revo software.

I understand that most people prefer to leave the N75 valve in the loop even with a MBC, which is what I'd do if mine were working properly. I just don't want to have to buy a new N75 valve if the MBC can take it's place or if I can get away with keeping the old one. If I do leave the current N75 valve in place along with a MBC restricted to a safe boost level, will this likely remedy the problem and possibly fix the code that keeps coming back?

CCA4, when you say you have a foot of vac line looped on the N75, do you mean that you just plug the N75 into itself with two of the three ports?

 

Correct. This will keep it from throwing a CEL. Don't hold me to this but off the top of my head I think it's the two short ports on the N75 that need to be looped together

 

That makes sense because the long port goes into the TIP. I'm assuming you keep the long port plugged into the TIP?

 

My MBC is plugged into the TIP, the N75 is just tucked up out of the way behind the passenger's side head light

 

So the other port isn't plugged into anything?

 

Correct.

 

My mbc is of w/g and turbo. Tip is plugged. N75 is looked( 2 short posts).