wont hold boost
 

I have a 1991 Supra Turbo. I've got all the upgrades including lexus afm, stage 3 ct-26, manual boost controller, custom exhaust,mhg,550 inj,custom fuel pressure reg,greddy blow off valve and walbro fuel pump. I noticed when I took it to the track this weekend that it would not hold boost when I would first launch it would go to 15 then drop to 11. So after the first run I turned the boost up a full turn which is equal to 4 psi. Ran down the track agian and the same thing 15 to 11. So the next run I turn the boost up again and again the same thing 15 to 11. So I checked all my hoses, vaccum lines and even check the boost controller and I cant find anything wrong. Its not smoking at all and idles good. Anybody have a clue as to what is going on? Thanks for any suggestions cause I'm stumped.

i think you missed a line somewhere . even a little tiny hose on the opposite side of the engine will cause this boost leak

u only run 4psi thru ur car? u said i turned it all the way up which is equal to 4 pai. 4lbs in a set up like that?

he said he turned it up a full turn, not all the way up.. a full turn seems to be equal to 4 psi.

what i would do is with the car running, open the hood and either have someone rev it, or you can do it yourself with the throttle linkage, and rev it till it boost and listen for a leak. if you cant hear one then find the vacuum line diagram on the tsrm and check all the lines. let us know hoow it goes.

Thanks I'll check it this weekend and let you know.

ill go ahead and post the vacuum diagram for you so you dont need to waste time looking for it, plus the more im on here the less i have to do homework :offwall: here ya go. taken from http://http://www.cygnusx1.net/Supra...cuum_hose.aspx
that has all the other vacuum diagrams too (cruise control, heater, etc.)
http://www.cygnusx1.net/Supra/TechTi.../vacuum_2l.gif

Well I looked for a vacuum leak. Still cant find one. So when I started it to take a test drive I found that I had an exhaust leak from directly behind the turbo so I tightened it down and took it for a run. It got to 18 then dropped to 14. So Im going to replace the gasket and see if that cures the problem.

let me know if that cures the problem cause i have the same problem i tightened mine up and it still leaks so let me know

i've read
 

well i was reading i think either importuner and they tested a evo 8 and it lost as it got closer to redline heres the line from import tuner
((showed boost to climb to a peak 20.6 psi as it quickly tapered off at 6000rpm to 16psi then fell flat on its face to a mere 13psi at 7000rpm. ))
http://www.importtuner.com/tech/powe...ontroller.html

thats the website so the boost drop might be normal..but i could be completely wrong