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Old 07-04-2017, 01:02 AM   #1
awdboxer
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Default 2015 STI Stage 1+ low boost

So I currently have a Stage 1+ STI that can only hit around 10-12psi with the OTS Cobb map.. and I'm running out of ideas on what to check next.

But first, a little back story.

I purchased a 2015 STI about a month or so ago and I'm currently trying to get it etuned (Brentuning) but having issues reaching target boost with the Cobb Stage 1 +SF map. When I purchased the car, it had an IAG AOS, AEM CAI, Cobb EBCS, and Tomei UEL headers (wrapped) on it. I could swear when I test drove it I was able to hit around 17psi a couple times. I know, I know... don't buy a used modded STI. But I've had three Stage 2 WRX's in the past, so I'm somewhat knowledgeable.

Since it wasn't tuned, I babied it until the AP arrived.

After purchasing the AP and swapping the AEM out with the Cobb SF intake (didn't want to pay $300 for the stock setup and couldn't find a used one), flashing the stage 1+SF map, I'm now only able to hit around 10-12psi in S#. During the install, I also unwrapped the headers because I wasn't sure what the previous owner had installed.... surprise, Tomei UEL headers.

I reflashed with the HWG map, but still only hitting about 12-13psi.
Went back and forth a few times with Bren, they even cranked the boost up to like 22psi but I was only able to hit 15psi.

I've checked all the hoses/clamps around the intake and bpv. I've also taken the intercooler off and inspected the couplers and hoses and everything looks to be in good shape.

The EBCS was also inspected and verified the hoses are good and plugged into the correct ports.

I've reset the ECU a few times, but no luck.
So I'm kind of at a loss on what to check next.

Planning on inspecting the header for any cracks tomorrow. I noticed it was pretty oxidized after taking the wrap off.
Would wrapping it again help the boost issue a little?

I have an appt next week with a local shop to see if they can diagnose the issue, but wanted to see if anyone had any other ideas.

Current mods:
Cobb AP w/Stage1 +SF map
Cobb EBCS
Cobb SF intake
Tomei UEL headers
12psi
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Old 07-04-2017, 10:18 AM   #2
Charlie-III
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Do the stage 1+SF mapnotes list the EBCS? I believe the map has to support that.
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Old 07-04-2017, 12:50 PM   #3
awdboxer
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Quote:
Originally Posted by Charlie-III View Post
Do the stage 1+SF mapnotes list the EBCS? I believe the map has to support that.


The Cobb map doesn't, but the test map from the tuner does.

Would the car over or under boost if the ebcs wasn't supported by the map?
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Old 07-04-2017, 12:56 PM   #4
hondaeater69
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the car would severely OVER boost with an aftermarket EBCS on the stock tune. something is not right. have you checked all the plumbing for the BCS lines?
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Old 07-04-2017, 03:03 PM   #5
awdboxer
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Quote:
Originally Posted by hondaeater69 View Post
the car would severely OVER boost with an aftermarket EBCS on the stock tune. something is not right. have you checked all the plumbing for the BCS lines?
Ok, that's what I thought.

Yeah I've checked all the hoses going from the EBCS to the inlet, turbo, and WG and verified they're plugged into the correct port.

Could the turbo be going bad?
Is there any way to check it, besides taking the dp off and seeing if there's any play in the shaft?
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Old 07-05-2017, 02:09 PM   #6
Zcypot
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I remember having this issue, I even had the EBC replaced. Turned out my BPV was leaking internally. If you can test with a different by pass valve, or buy one and return it after testing if they allow it.
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Old 07-05-2017, 06:33 PM   #7
MedicDG
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Quote:
Originally Posted by awdboxer View Post
So I currently have a Stage 1+ STI that can only hit around 10-12psi with the OTS Cobb map.. and I'm running out of ideas on what to check next.



But first, a little back story.



I purchased a 2015 STI about a month or so ago and I'm currently trying to get it etuned (Brentuning) but having issues reaching target boost with the Cobb Stage 1 +SF map. When I purchased the car, it had an IAG AOS, AEM CAI, Cobb EBCS, and Tomei UEL headers (wrapped) on it. I could swear when I test drove it I was able to hit around 17psi a couple times. I know, I know... don't buy a used modded STI. But I've had three Stage 2 WRX's in the past, so I'm somewhat knowledgeable.



Since it wasn't tuned, I babied it until the AP arrived.



After purchasing the AP and swapping the AEM out with the Cobb SF intake (didn't want to pay $300 for the stock setup and couldn't find a used one), flashing the stage 1+SF map, I'm now only able to hit around 10-12psi in S#. During the install, I also unwrapped the headers because I wasn't sure what the previous owner had installed.... surprise, Tomei UEL headers.



I reflashed with the HWG map, but still only hitting about 12-13psi.

Went back and forth a few times with Bren, they even cranked the boost up to like 22psi but I was only able to hit 15psi.



I've checked all the hoses/clamps around the intake and bpv. I've also taken the intercooler off and inspected the couplers and hoses and everything looks to be in good shape.



The EBCS was also inspected and verified the hoses are good and plugged into the correct ports.



I've reset the ECU a few times, but no luck.

So I'm kind of at a loss on what to check next.



Planning on inspecting the header for any cracks tomorrow. I noticed it was pretty oxidized after taking the wrap off.

Would wrapping it again help the boost issue a little?



I have an appt next week with a local shop to see if they can diagnose the issue, but wanted to see if anyone had any other ideas.



Current mods:

Cobb AP w/Stage1 +SF map

Cobb EBCS

Cobb SF intake

Tomei UEL headers

12psi


Did u replace BPV gasket after you removed? They should be replaced every time they are removed and BPV bolts torqued to spec.
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Old 07-05-2017, 06:37 PM   #8
awdboxer
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No, the gasket wasn't replaced.

I'll order a couple and see if I can swap out the bpv with another.
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Old 07-10-2017, 10:55 PM   #9
awdboxer
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So I took the car into the shop this morning and.... no leaks.
They did a smoke test and didn't find anything.

Notes from the shop:

Test drove vehicle, hit 16.3psi in 3rd (on the test map that Bren cranked up to 22psi).

Removed wastegate signal line and test drove, hit 21.2psi in 3rd (again, on the test map... so it looks like the turbo is fine).

EBCS inspected and verified it's installed correctly.

Compression/leakdown results:

Cyl1 - 13%, 118psi
Cly2 - 14%, 111psi
Cyl3 - 13%, 120psi
Cyl4 - 18%, 110psi

They said everything looked great but the results seem a little low for a 2yr old car with 26k miles on it. They said anything under 110psi needs to be inspected further and anything under 100psi needs to be re-built.

Their recommendation is to get a catless downpipe since there's a lot of restriction after the turbo, but none before since I have the headers and uppipe.
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Old 05-13-2018, 09:04 PM   #10
hoang5659
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any update on this thread? i am having a similar issue. i have a 2015 STI with borla catback, cobb intake, GFB response BPV and cobb stage 1 tune (OTS). I can only get 8.5 psi peak boost.
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Old 05-14-2018, 09:34 PM   #11
awdboxer
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Quote:
Originally Posted by hoang5659 View Post
any update on this thread? i am having a similar issue. i have a 2015 STI with borla catback, cobb intake, GFB response BPV and cobb stage 1 tune (OTS). I can only get 8.5 psi peak boost.
Yes! Sorry I never updated this. So I’m not completely sure what fixed it but I replaced the bpv gasket, swapped in a new oem boost controller with new hoses, and intercooler hoses. After that I was able to hit full boost every time and haven’t had any issues since.

Have you tried resetting the ecu and flashing back to the stock map then to stage 1? Or swapping the GFB back to the stock bpv? New gaskets?
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Old 09-10-2018, 09:06 AM   #12
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Last edited by hoang5659; 09-10-2018 at 09:13 AM.
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Old 09-10-2018, 09:12 AM   #13
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