I have a 2016 STI with a Cobb Cat-Back and Cobb SF intake. I also have an Accessport which I used to do their Stage 1+SF OTS map. I saw boost levels around 18.5 to 20psi.
Lately my car struggles to hit 18. It usually stays around the 15-16psi range while in S#. My car has under 5,000 miles on it.
from the very vauge description, it sounds like it could be a vacuum leak. did you do the installation yourself?
but your car is brand new and under warranty, take it to your dealer. the more you work on your own car, the more of a chance subaru will deny your claim.
Definitely should check for a boost/vacuum leak then. I would suggest starting to look at the couplings on all of your hoses. The changing temperature could have caused a loose one to develop a small leak. Good luck and happy hunting. Typical methods include:
Soap and water (for boost leak)
Smoke test (both!)
propane... (I do not advise this one, and will also only find vacuum leaks)
Visual inspection/Just touch every coupling (time consuming, but sometimes is all it takes)
EDIT: I even read this and didn't even remember it was already said...
Boost levels that high in the first place sound off to me. Cobb Stage 1 tunes typically run close to 17 and Cobb reports that that is only when in S# mode.
Im curious if the ECU/map might be reading something thats off and opening the waste gate arm prematurely to help drop your boost into a range thats closer to target boost. How long have you been running that map?
Last question have you completed any 3rd or 4th gear pulls and logged them? can you upload them so we can have a look. It sounds like you were over boosting at 18-20PSI and the ECU has settled in as it learned ( the first 50 miles or so )
IMO this sounds more like the ECU is learning than anything else. If you want to test if its ECU learning you could re-flash your Stage 1 map and see if the boost starts spiking up high again but I wouldn't do that unless you have good quality 93-94 octane fuel to play with ( 95 or a race blend would be better ). 3 pounds over target levels could outrun your injectors which may in turn cause a lean condition and can cause premature damage to your engine.
The target boost for the Stage 1+SF is ~18psi +/- 1. So should range anywhere from about 17psi to 19psi.
I have been running the map for a few months. I tuned it back in March and this happened mid to late June. The car was driven a couple thousand miles on the tune before the boost change occurred.
I reset the ECU learning but kept the tune in place to see what that did. It did not have an impact. I then reset the entire ECU and retuned it back to the stage 1+sf tune and that also did not have an impact.
I will be doing a 3rd gear pull today and I will upload the datalog and will also be sending it into Cobb at their request.
I was running the normal wastegate map. I changed it to high wastegate at the request of Cobb to see if it changed the boost. It did not have an impact.
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