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Discussion Starter #1
2010 STI hatch 6 speed. 2.5T, catback exhaust, CAI. 91K miles.
My issue is boost loss. So here’s what it does followed up with what I’ve already tried.
It sometimes does it while im driving, in between shifts or I’ll have boost, turn the car off, go drive again later and it’s gone. But it cuts boost down to 1psi in sport mode and 3psi in sport sharp when it does this. Any gear, any rpm it limits it to those numbers depending on what driving mode I’m in.
I have a cat back exhaust, cold air intake, and I’ve noticed the previous owner had removed the purge valve for the evap system although I have not once gotten an evap related code. The only Code I do have that comes on and off randomly is a park/neutral switch code that I haven’t gotten around to fixing due to it being such a pain in the ass on the manuals (on top of the tranny.)
maybe when there is a fault code it automatically cuts boost as a fail safe?
I’ve replaced the EBCS, plugs and coils, and replaced any ripped or damaged turbo/intercooler/throttle body couplers. I have also done a throttle relearn which fixed the issue for about a week then lost boost again. To make it all the more confusing to me, regardless of if the check engine light is on or not, if I disconnect the battery and reconnect I will have boost for a little while, but it will go away. Also, if use my scanner and clear the codes, regardless or if there is any active codes or not, I will have boost for a little while. I’m stumped on where to look next besides a smoke test, but I don’t believe I have a boost leak due to the fact that electronic procedures will temporarily fix the issue but maybe I’m wrong.
Smoke test, injector drop test, and turbo inspection are up next. Let me know if there is any test I should do or if anyone has had similar issues. Thanks
 

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I do understand your logic for the thinking of being an electronic issue but i still think you need to smoke test the engine. This could be as simple as a BOV gasket leaking which are notorious for doing so. At 91K its also very possible the turbo inlet could be leaking. When you say you have boost for a little while after doing a battery reset, are you getting the full amount of boost you should be getting or just a couple of psi?

Im wondering if the turbo maybe worn out at this point or maybe a wastegate issue.. Have you done any visual inspections on the turbo itself? Have you checked the exhaust wheel and wastegate actuation? How is the car running in general? Is the car tuned?

There is alot to cover on this but i think you need to FIRST start with a smoke test and verify that there are no leaks before moving on.
 

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"Always start with a smoke test" and in my experience even that may not expose a leak. It's still the place to start.

As Jay suspects, your cars symptoms sound like those of a "simple" boost leak, not electronics.
 

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Discussion Starter #4
I do understand your logic for the thinking of being an electronic issue but i still think you need to smoke test the engine. This could be as simple as a BOV gasket leaking which are notorious for doing so. At 91K its also very possible the turbo inlet could be leaking. When you say you have boost for a little while after doing a battery reset, are you getting the full amount of boost you should be getting or just a couple of psi?

Im wondering if the turbo maybe worn out at this point or maybe a wastegate issue.. Have you done any visual inspections on the turbo itself? Have you checked the exhaust wheel and wastegate actuation? How is the car running in general? Is the car tuned?

There is alot to cover on this but i think you need to FIRST start with a smoke test and verify that there are no leaks before moving on.
After a battery reset or clear codes on the scanner I get full boost. I don’t believe it’s tuned (bought used) just based on the fact that peak boost in sport sharp is 13psi which I’ve heard is pretty much stock boost levels. I haven’t done any visual inspections, which I need to do. I’ll probably get some time to atleast do the smoke test at work today. Overall the car runs good. When it has boost it runs beautiful and pulls hard. But right before I lose boost I can feel it start not pulling as hard, boost seems to take longer to build up, and it basically falls on its face right before I lose boost, then I’ll shift and boom no boost.
I’ll smoke test today and update. Thanks for the advice!
 

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First off, you're asking for trouble if it has an intake and its not tuned, I would figure that one out first. Do you have any data logging ability?
 

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Discussion Starter #6
First off, you're asking for trouble if it has an intake and its not tuned, I would figure that one out first. Do you have any data logging ability?
The only data logging ability I could use is taking a picture of live data on the shop scanner. I just have a little one for checking codes with very little features. What monitors/data would be most helpful to look at?
 

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Discussion Starter #7
Bit of a busy day today so I didn’t have time for a smoke test. Hoping to smoke test it before the week is over. I will update when I get to it. In the meantime I’ll keep checking this thread for any more tips. Thanks to all!
 

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with that fault code would suggest check the wiring as its easy to damage when pulling engine or swapping clutch...
 

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Discussion Starter #9
Just got done with the smoke test. No leaks. My coworker pointed out something that I didn’t consider which is that if it has been tuned, which I do not know if it is, some monitors may be turned off which then wouldn’t give me a fault code for some things. So my next question is, is there a way to tell if you have a tune? Or should I just book an appointment with my local tuner which would either be PRE racing or ETS?
 

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Discussion Starter #10
with that fault code would suggest check the wiring as its easy to damage when pulling engine or swapping clutch...
I’ll keep this in mind when I get around to changing that sensor out
 
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