Boost Falling Off. Any Ammount down to 10psi

[Jordanbutter]

So my prblem is just different enough to start a new thread. I was running my Evo III 16g at 16psi and one day it went up to 16psi and then fell back to 10psi and it has done it ever since. I have checked all I can think of. Boost leak test, checked for exhaust leaks, replaced boost controller, replaced boost lines, shimmed the wastegate with two washers on each bolt, pulled the boost lines and it spooled to 20psi and then I let off the gas. I can't figure out why its doing this. Any suggestions for problems or tests to run would be great. thanks!

 

[rich3389]

Possible wastegate actuator.

 

[eclipse_turbo97]

I would like to know what the answer is! My fp t28 is doing the same exact thing. Change basically everything that he did to check it and still no cure.

 

[silver bullit]

Boost creep have you heard of this?

 

[rich3389]

How is this boost creep, maybe you mean boost spike?
The OP said that he has been running a solid 16 psi then one day went down to 10 after hitting 16, It doesnt sound like it could be boost spike to me unless somehow the boost controller got turned way down and it happened to be spiking at 16 before but didnt notice it.

 

[Jordanbutter]

Thanks. Its not boost creep or spike cause yes it was running perfectly untill that day. So let me guess if it is a faulty actuator the only fix is to replace it huh? $$$

 

[eclipse_turbo97]

mine was running fine on about 17 pounds when I first got my car. Then one day it shot up to 17 and just fell and sat at around 12psi. Changed boost settings, boost controllers, even did boost leak test. Couldn't figure out a thing. I thought it might be the stock smic, so I change it to a short route fmic. Still didn't do a thing. Guess I will be ordering the 17psi fp actuator for the t28.

 

[Boost Demon]

I think it's the WG also, but you may want to check one more thing. Mitsubishi turbos are notorious for developing cracks on the hotside around the WG passage and down the throat of the turbo/manifold flange over time. If you've had your turbo for awhile or bought it used, it may be worth a quick check.

 

[T9S1i]

Yeah it has to be something with the wastegate, either the actuator, or the flapper.

The next two tests that i would do are these:

First: take a look where your actuator arm mounts to the flapper on the turbine housing. Sometimes the little cyl shaped piece that is inside the turbine housing that connects the flapper inside the housing to the pivot arm where the actuator rod connects will sort of "walk" out of the housing. You will know it when you see it. It should look like its out 1-2mm, if its out farther than that then tap it back in with the side of a hammer. If it walks out it wont let the flapper close all the way which results in slow spool and flakey boost control.

Second - a little more complicated... add 9psi of pressure to the wastegate actuator and see if the arm moves over and stays over, it might initially move, but not hold, if thats so the diaphragm might be shot.

Last. (sorry 3 sugestions) viually inspect the turbo for shaft play. None? pull the turbo and check the turbine housing. I had a bullseye 38mm internal gate housing and the flapper kind of just broke, i couldnt build 12psi barely by redline. I took that f'r off and welded the hole shut and went external after that. You can also check the flapper area and turbine housing to see if there is any excessive cracking.

I would only do these three if you have actually already done what you said you did in your first post. Those are the first things i woul have done. ( boost leak test, vac lines to mbc, shims for wasteate)

Good luck, i hope its an easy fix


edit* one more thing i thought of. If you are running a ball/spring type mbc, take it apart and check the internals, maybe the spring is fubar or something...

 

[Jordanbutter]

I will take a look at all that stuff when I get a chance. The turbo was bought brand new only about 3 years ago so if it has shaft play and all that already I'll be so pissed, but I will check. As far as a slow spool though its exactly where it normally is 16psi @ ~3500rpm, so thats not really a problem. Its not the MBC I've had 4 different ones in it (I keep taking all my friends) and its always the same story. What would you use or how would you apply 9psi to the actuator? I'm trying to think of how to set it up but I can't.

 

[T9S1i]

hmmm not exacty sure how to add exactly 9psi to the actuator, i would assume there has got to be some kind of pressure regulator setup for an air compressor.

If you dont want to pull the entire turbo to check the integrity of the flapper door you could always just drop the o2 housinpg, unhook the wg rod/arm and manually modulate the flapper with your hand, thats what i did to figure out that moving the flapper outside the turbine housing did not actually move the flapper door. sometimes they just go faulty like that. all ou would have to do then is swap to another turbine housing.

 

[Jordanbutter]

Ok I was able to test the actuator today and it opens and stays open at 9psi untill I bleed the air off and then it snaps shut. So I tried to take the turbo off to inspect it but one of the turbo to manifold was stuck. It comes out a bit and gets stuck now I don't want to force it out and possibly break it now but it looks bent a bit. At closer look it is leaking a bit of exhaust out the back twards the block so ARP here I come. Hope thats all thats wrong.

 

[T9S1i]

you can also just take off the o2 housing and try to look at that side to check the wastegate opperation.

 

[joe]

Ok I was able to test the actuator today and it opens and stays open at 9psi untill I bleed the air off and then it snaps shut. So I tried to take the turbo off to inspect it but one of the turbo to manifold was stuck. It comes out a bit and gets stuck now I don't want to force it out and possibly break it now but it looks bent a bit. At closer look it is leaking a bit of exhaust out the back twards the block so ARP here I come. Hope thats all thats wrong.

If you are talking about ARP exhaust studs then good.
If you are talking about ARP turbo to exhaust manifold bolts I wouldn't recommend them many people have had problems with them breaking..

 

[Jordanbutter]

Thanks for the heads up cause I was looking at the turbo to mani bolts. What do you suggest for bolts?

 

[DirtyBirdRacing]

Thanks for the heads up cause I was looking at the turbo to mani bolts. What do you suggest for bolts?

OEM with antisieze FTW.

Bill

 

[desolateboosted]

depends if it's an ebay turbo or not, ebay turbos are nortorious for odd changes on boost levels.