overboosting, new mbc

[talonite]

ok so just today my car overboosted like CRRAAZZZYY it was set for about 14psi on a cheapy ebay MBC, but yet it built boost to around 24 to 28psi. so i figured that was the problem. bought a new grimmspeed MBC from MAP thinking it was gonna be a clear solution. but it is still doing it. im running an evoIII turbo with the stock internal gate on it. any ideas on where to start? I mean i triple checked and everything is hooked up correctly, and I'm just kinda stumped at the moment.

[goodhart]

You're sure you have it turned all the way down and not all the way up right? LOL. Have you tried replacing the vacuum lines you have connected to it?

[scheides]

Make sure it's not backwards.

Then try running south the line directly from the boost source to the wga, maybe it's boost creeping really bad?

[asshanson]

My first guess is a leak in the hose from the intake manifold to the MBC. Could also be a broken wastegate actuator, like a hole in the diaphragm.

[Shane@DBPerformance]

Don't run any boost controller, just a new vacuum line and see what it does. You might have a wastegate actuator problem though.

[19TsiAwd90]

had the same issue scared the shit out of me when i was getting on the freeway and i saw my boost gauge spike to 29psi =) it was fun for a second lol ended up being a hole in the wastegate line i would check that first, i have a grimmspeed mbc and it works flawlessly..

[talonite]

ok, so went through checked all the lines, the one from the mbc to the wg actuator was rubbed a little bit wasnt leaking, but i replaced it anyways. still doing it. used the smoke machine at work to do a boostleak test, doesnt seem relevant but i have a couple small leaks from my throttle body and b.o.v. i don't think they would relate to an overboost issue but i thought it was worth a mention. now would there be a way to manually test the wastegate actuator, or is it gonna come down to dissasembling it?

[goodhart]

Take out the MBC and put the vacuum line from the nipple on the j-pipe/compressor housing straight to the wastegate actuator (what scheides already mentioned) so it runs on wastegate boost. If it still goes to 29psi, either you have a magical 29psi actuator or a bad one.

[Shane@DBPerformance]

You can extremely carefully apply pressure from an air compressor to the port on the actuator and see if it starts opening when it should. A temporary boost gauge on the line going to the actuator would help a lot. Just don't try to put 50+psi to it, you would want to slowly ramp up the pressure.

[talonite]

if i go straight from the j-pipe to the actuator wouldnt it just build max amount of boost? or does the actuator itself have a limit? sorry about the newb questions here.