need help overboosting problem

[danbosman]

hi i have a 1990 shelby tona and i cannot seem to figure out why my boost keeps going past 15psi on the gauge i even tried putting a manual boost valve in and it still does it. if i close the valve all the way it only boosts up to 5psi. when its slightly open it overboosts then starts going down im stuck and cant think of anything else.
if someone could chime in with some help that would be great
thanks

[tryingbe]

New to you car?
When did the problem surface?

[danbosman]

Well I changed the engine and transmission and took the whole vacuum system out as one piece and I made a video of how everything went back together and any way I have my manual boost control valve hooked up and I know its right cause I hooked it up on my buddies car the same way and it worked fine. Could it b my waste gate can?i know the rod is still on the swing valve.

[danbosman]

I am new to turbos

[sinfulrelations]

what type of mbc are you using??

[NAJ]

I will get you 2.5L T-1 Diagnostics by tomorrow morning.

[tryingbe]

Quote:

Originally Posted by danbosman if i close the valve all the way it only boosts up to 5psi. when its slightly open it overboosts then starts going down

If the vacuum lines to the MBC is reversed, it will do that.

[NAJ]

I am also assuming this is a stock setup with the stock exhaust.
On the 2.5L T-1 and the 2.2L T-4 VNT the exhaust was engineered to be part of the boost control system.
If you lower exhaust backpressure the Mitsu turbo will overspool.

[NAJ]

OK..Had time today before I had to leave ...
















PRESSURE TESTER
http://www.tooltopia.com/mityvac-mv8500.aspx

[danbosman]

Its a cheaper one it was like 30 bucks. Its call boost controller high performance. And yea I've heard of the back pressure thing withe Mitsubishi Turbo but I had the same set up on my old engine and it worked fine. The only difference in the exhaust is that there is a test pipe in place of the cat but it was also like that on the other engine. Thank you for the images. Oh and one more difference I swaped it to a manual trans as well

[paulharbosky]

wastegate flapper door may be stuck. easy way to see if WG is the prob. hook up straight vacuum to WG nipple(no check valve no orifice)make sure ur getting vacuum. when boost pressure builds in vac line it should open the swingvalve and youll get 5-7 lbs of boost. if it still overboosts take off WG can ad try to move the swingvalve. it may be seized. if it moves change wg can and perform same test. when you get 5-7 lbs doing this look to you boost control setup. try simple maual setup(use restrictor ..... makes it much more responsive)

[danbosman]

I know the swing valve is moving because I moved it with the actuator rod off

[paulharbosky]

Quote:

Originally Posted by danbosman Its a cheaper one it was like 30 bucks. Its call boost controller high performance. And yea I've heard of the back pressure thing withe Mitsubishi Turbo but I had the same set up on my old engine and it worked fine. The only difference in the exhaust is that there is a test pipe in place of the cat but it was also like that on the other engine. Thank you for the images. Oh and one more difference I swaped it to a manual trans as well

I bought one of these (high performance boost controller)on ebay a while ago. bottom line....junk. it will absolutely not work the way they show it hooked up in the instructions. my advice throw it away. use the stock boost controoler till u can get a better one. if you want to try to make it work you have to hook it up like this:
Simple bleed system

Doesn't get much simpler then this- The restrictor keeps you from having to have a MASSIVE bleed to open the wastegate enough and the check valve keeps you from having a vacuum leak when not under boost.

Problem- Boost goal may or may not creep past set point and spiking maybe and issue. Very sensitive to restrictor size, playing around with different ones came minimize problems and achieve desired results. Also boost pressure can prematurely start to open wastegate with this setup slowing spool time, not really an issue with most wastegate cans that have the heavy spring, could be an issue with some cars though.

Note- The bleed valve in this system can be mounted inside the car which is handy for fine tuning desired boost level. (from thedodgegarage.com)

[danbosman]

thank you guys ill try these things when it stops blizzarding out here. i appreciate the help and ill let you know what i come up with. and id post some pics but i cant figure out how to lol.