Hey guys. So I've been dealing with a boost problem for about a month or so now. My guage is reading a spike of 25-27psi and tapering to about 11psi. This problem started when a friend and I installed a buschur mbc and a boost gauge. I've tried various things (i.e. switching the lines/boost leak test) but to no avail. At this point I'm just frustrated and have no clue what to do next. If Anyone can link up with me and assist it would be thoroughly appreciated. Hit me up. My name is Jaraal: 562-291-8529.

 

Wowzers. That's a big spike and a lot of taper. Admitting how hard it is to diagnose problems like this over email, here is some wild guessing. The taper to 11psi...is that at full throttle? Or when you see the 27 psi spike, are you like OH CRAP and you get off the throttle a little? If the latter is the case, it may be that your MBC is just set too high. When you first installed it, did you have it dialled all the way down? A completely dialed down MBC should cause the waste gate to run at turbo pressure and peak at about 12 psi.

When you say "switching the lines" what do you mean? Are you not sure the MBC is installed properly? The Hallman I have was pretty easy...one line goes to the compressor outlet, the other to the waste gate actuator. The line from the stock solenoid to the intake pipe is removed, and the nipple on the intake pipe is capped. You should verify proper installation with someone that's done this before, first thing.

 

Well. It's more like the latter of the two for the spike problem. I'm like oh sh*t and let up a little and get back to wot and then it will hold to 11. When I first installed it. The screw was turned all the way out. As in, if I would have loosened it any further it would have fallen off. As for the lines. One line goes to the wastegate and the other to the turbo outlet. I followed the instructions perfectly. However, after having the problem and discussing it with a few ppl on here. They said to switch the lines. That still didn't work. I even tried other ppl's mbc's to see if it was just mine. Still a no go. In regards to the line from the stock solenoid to the intake, I removed that in initial installation and capped off the opening on the intake. I also capped off the openings on the stock boost solenoid.

 

So you tried someone else's MBC and it did the same thing? Also a Buschur or a different brand? I was suspecting a defective MBC but if it's doing that with any old MBC, it might be the waste gate itself (yikes). Once again with the disclaimer that this is over text and who knows if I am totally off base.

Also you mentioned it was completely dialed out when you first installed the guy. Did it still do this "27 and then 11" behavior then? When you reversed the lines, did you also start dialed completely out? As in, no matter how you adjust the MBC, it does the same thing?

But it sounds like SOMETHING in your setup is "sticking," as in it's doing nothing until you spike up to 27 or so, then it flies open and stays open. 11 psi is right about what you'd expect to run if an MBC were dialed completely open (I said 12 in my previous email but close enough).

 

I'm running the BR mbc. I have somewhat the same thing happening, but my boost only spikes to aout 24 and then tappers to 21 in 4th gear wot. at 3rd gear wot it holds 21 psi. It lokks like you got everything hooked up the way I do. No idea why you would spike and loose all that boost though. Best thing to do is call Buschur. As long as its their product they'll help you out! They did for me, but thats just because I'm a spaz and wanted to dbl check the instructions!

 

Yeah, I tried my friend's Forge, and it did the same spike/taper thing with his supposedly set to 20psi. It's as if the mbc isn't even controlling the boost. When I reverse the lines testing with the buschur mbc it still has the same spike/taper. Basically, no matter where the mbc is set, it does the same thing each time. I figured something might be stuck. A friend of mine said you need to compress the spring inside the mbc like 30-50 times. I did that and still a no go. I'm gonna call a shop today called engine logics and see if they can help

 

Yeah, I called buschur and they have told me to do what most others are saying. Switch the lines and do a boost leak test. I've done both of those things to no avail. This really sucks a$$

 

Yipes. I have a couple suggestions.
1. Connect the compressor outlet directly to the waste gate actuator (remove the MBC from the mix). That should cause your boost to never go above 11 or 12. If it still spikes when hooked up like that, then the waste gate itself may be shot, though that's not typically something that "goes out." It could also be some sort of restriction in the hose connected to the waste gate. Take it off and try blowing through it by mouth.

2. Try blowing through the hose connected to the compressor outlet by mouth. You should be able to do that unrestricted. I know the stock hose has a little brass pill in it...you're supposed to take that out if you hook up an MBC, but if you didn't, maybe the pill got turned and is restricting things?

Good luck man. Sux to have your awesome car not working right. If it is behaving totally the same regardless of which MBC you use or how you hook it up, I don't think anything Buschur tells you to do to the MBC will help.

P.S.
That's actually how things are supposed to work. You'll always have some taper, but 27 is too high (esp for an MBC dialled all the way out), and 11 is too low. My Hallman peaks at 24 and tapers to 21 at redline.