Cant boost below 20psi

[HyperGSX]

I'm on the t25 right now with basic boltons, even with the mbc closed all the way it will still boost all the way upto 20psi. I checked the lines on the mbc and they seem ok, is my wg actuator damaged? What else could it be

 

[98eclipseRS]

Pull the mbc out of the equation and see if that does anything for your situation. You also will want to check to make sure the wastegate actuator is workign properly.

 

[DSMcamaro]

If it started doing this right after the MBC install, it probably means your boost controller needs some tweeking or is hooked up wrong. If it just started acting up and you've have the boost controller hooke up for a while, I would check the actuator like stated above or possibly try a differnt MBC.

 

[kenamond]

I agree. You may be turning the boost all the way up when you think you're turning it down.

If you can run a vaccuum line from your T25 compressor straight to your WGA, you should see around 11psi boost. If you see 20psi still, disconnect your WGA arm from the lever on your turbine housing and make sure the lever turns with your fingers (cold motor only!). If the lever doesn't turn freely with your fingers, it might be getting stuck and not opening (disobeying what the WGA is telling it). If it turns freely, you can do a run and shouldn't see more than a few psi boost.

If all of that works out fine, make sure you've connected your MBC up correctly. If you pull it out and loosen it all the way, you should be able to blow through the input side and leak out the other end. As you tighten it, you'll get to a point where you can't blow through it and get a leak out the other side.

Just keep in mind that if you run the vaccuum lines backward, the MBC won't ever open, and you'll have absolutely no signal running to the WGA ever. That's bad for the turbo (running 20psi on a T25 is way beyond its efficiency range) and your motor (the T25 will be blowing very hot air at 20psi and probably causing knock and huge timing retardation).

Also, you shouldn't be T-ing into the BOV line for your MBC input. Rather, you should get the input straight from the compressor housing and then feeding straight to the WGA nipple. Some also get their input from the IM, but I personally don't think that's the best idea.

Try those things and let us know what happens.

 

[DSMcamaro]

Also, you shouldn't be T-ing into the BOV line for your MBC input. Rather, you should get the input straight from the compressor housing and then feeding straight to the WGA nipple. Some also get their input from the IM, but I personally don't think that's the best idea.

Not to go way off topic but I used to have my MBC T-ed off of the BOV line and it worked fine, but after reading on here that it had negative effects on the bov, I switch it to a nipple I welded in my intake piping and I found the BOV would open pre-maturely this way. (MAFT set up, so I could hear it opening/leaking) So I hooked it back up off the BOV line. Just my .02/ personal experience.