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Discussion Starter · #1 ·
So I am stumped. I have been having power and boost issues with my ST. I have done everything I can think of to fix it. I can hit maybe 18 psi at 3-3500 rpm on WOT but it quickly tapers off and I end up at around 10 psi at redline. On partial throttle, I have some strange boost fluctuations around 5-10 psi, like the boost needle will be bouncing up and down between 5-10 psi.

I did some research and tried all the common fixes that I could find:
- I pressurized the system from the turbo to the intake manifold to 22psi and found no leaks
- I had the wiring harness splice repair
- I replaced my used Boomba BOV with a brand new Mountune BPV (thought it might be leaking)
- I replaced both solenoids
- I reset KAM data
- I installed multiple different tunes
- I cleaned my intercooler and all of the piping.
- After none of this helped, I figured the only thing left to replace was the turbo. I bought a used one with 8k miles and installed it.

Even after all this, I still have the same low power and boost issues. The only thing I can think of now is maybe I have some sort of fuel or ignition problem. Even though I have no negative corrections and AFR seems normal.

Any insight or suggestions are appreciated.

Mod List:
Cobb Intercooler Kit
Green Filter
Mountune Turbo-back catted exhaust
Mountune BPV
Cobb Accessport with Stage 2 93 octane OTS Tune
 

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Have tried to preload your WG? If not give that a shot. Let your tuner know because he will need to update your tune for it.


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Discussion Starter · #3 ·
I haven't tried that. Would that just be a band-aid though? I thought it might be a WG actuation problem as well but I was hoping that would be fixed when I replaced the turbo, wastegate, solenoid, and tune.

I have been running the same tune for a year and it didn't become a problem until a couple months ago. I can't figure out what could have changed.
 

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I know higher elevation will cause things like this. Have you moved in the past few months? Also want to get rid of your old turbo? pM me if you do. I’m looking fo a stock one.


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I know higher elevation will cause things like this. Have you moved in the past few months? Also want to get rid of your old turbo? pM me if you do. I’m looking fo a stock one.


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PS, Not sure the wg preload is for you in this situation I’d hold off on doing it - at least until you get to the bottom if what the cause is. Silly question but have you verified sure you are on the performance map slot and not the eco map slot? As far as the weird fluctuations go might do a few datalogs and post them on here to see if someone can see something that stands out. Lots of helpful cats on this forum

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Discussion Starter · #6 ·
I know higher elevation will cause things like this. Have you moved in the past few months? Also want to get rid of your old turbo? pM me if you do. I’m looking fo a stock one.


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PS, Not sure the wg preload is for you in this situation I’d hold off on doing it - at least until you get to the bottom if what the cause is. Silly question but have you verified sure you are on the performance map slot and not the eco map slot? As far as the weird fluctuations go might do a few catalogs and post them on here to see if someone can see something that stands out. Lots of helpful cats on this forum:)

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I haven't moved or anything.

I did check to see which tune slot I was in, but I am gonna double check now that I'm paranoid lol.

I'll post some data logs later this week. Thanks for the help!
 

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I haven't moved or anything.

I did check to see which tune slot I was in, but I am gonna double check now that I'm paranoid lol.

I'll post some data logs later this week. Thanks for the help!
I find myself double checking a lot due to the map switching ability.


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Discussion Starter · #9 ·
I figured out the problem. I meant to post a datalog sooner, but here it is.

It turns out I had a bad throttle body. Below you can see where I have plotted throttle position (ETC Actual) and boost. The position of the throttle plate was fluctuating with boost pressure. Sure enough, replacing the throttle body fixed it, power problems and all.




Text Line Font Diagram Slope
 

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Wow what a simple solution, sucks you had to go through all that to figure it out.

I'll keep this one in the back of my mind.
 
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