Update 10/17: Upon months of frustration, I finally hunted down the problem. It turns out that my Up-pipe heat shield was extremely loose and ratting and under certain RPMs it would create false knock. In reviewing my learning view logs, it seems to happen <3000rpm where it would show almost -12 correction in that table with the DAM/IAM at 0.000.
I was able to zip tie the heat shield to somewhere in the engine bay to test out my theory. (I wasn't about to pull the up-pipe for no reason) reset the ECU and viola 2 weeks and it was running stronger than ever.
Yesterday, I went to my local exhaust shop and had the heat shield on the up pipe re welded and everything is good so far. Since the stock heat shield actually holds together some of the up pipe heat shield, removing that to install an aftermarket DP and time will loosen the up pipe heat shield.
So in Conclusion, check ALL of your heat shields and get rid of any rattles in the engine bay.
Good Luck to anyone having the same problem...
– 2006 STi – 130k miles:
Stock Air box w/Panel filter
NGK Spark Plugs (Stock heat range)
Catless DP w/ SPT exhaust
Stock BCS + Restrictor Pill and Lines
Custom CA91oct Stage 2 XPT Road Tune (NO LC + FFS) Tuned at Sea level ~76F, ~20PSI MAX
Walbro 255lph Fuel Pump
Various TiC Bushings, Group N mounts, and Braces
RCE Yellows on stock struts
Whiteline Front + Rear Sway bars (Stock End links)
My car is primarily a daily driver with multiple track + Auto-x throughout the year.
The car lives in Southern California and is driven mostly on the freeway at sea level; it will see 5000ft occasionally going through the mountains. I get around 280-300 miles to the tank.
I have done weeks upon weeks of research on NASIOC, IWSTI, CLUBWRX, GOOGLE etc... so before you say “search is your friend”, link me to www.lmgtfy.com
, or “call your tuner/get a new tune” I did my research to the best of my ability and have been diligently putting this together to find an answer and solve it for everyone who has the same issue. I ask that you do not flame, be rude, e-thugging all over my thread, please know that I am asking for help/suggestions and don’t need any disrespectful answers as I have no problem ignoring you, reporting your post and getting you in NASIOC time-out.
Upon my research, there have been several threads (which I will link later below) with people having the same issues. It is also not limited to Subaru’s as it affects boosted cars such as GTRs (Nissan calls it “Low Boost Mode”), DSMs, older 2.2 Subaru turbos, Aftermarket turbo’ed Vettes. All the threads lead to some kind of progress but NO end result regarding a solution.
At any given time when cruising on the freeway at 65-75mph my car will only produce 10psi (wastegate boost). It occurs randomly as I can be doing WOT pulls on the freeway and it will boost fine. Sometimes it can go days/weeks without anything happening and one day all of a sudden it will just boost to 10psi. This occurs with the AC on or off and in temperatures ranging from 55F – 100F (yes, we see 100F in SoCal sometimes) However, if I go up a grade putting load in 5th or 6th gear @ ~5psi the ECU relearns and I am able to boost back to 20psi. On occasion if I turn the car off and on it will boost back to 20psi.
I have had this set up for over 100k miles and this issue only started to show up around 123k miles. When this first happened, I brushed it off and reset the ECU thinking it might have learned something weird or a bad batch of gas. I became concerned after the next few times after I reset the ECU the issue came back. This is where I began my search…I have logged and will post later (using ROMRAIDER logger/ Learning View Tool). When the car boosts to 20psi the IAM/DAM is at 1, when it boost only to 10psi the IAM/DAM is 0.
I will go into detail what I replaced and the results below but to keep it simple I have replaced the BCS with a OEM, I replaced the vacuum lines with a brand new set + pill from the dealer. I have replaced the Knock Sensor. I have flashed to a different Stage 2 map.
What I have done/replaced (In order)
– Self-explanatory, reset it with suspicion that it learned something weird or bad batch of gas.
Checked for Leaks
– Did my best in checking for leaks without a smoke test. All lines intact with no cracks.
Boost Control Solenoid
– Upon initial research there was a possibility that my BCS is failing although there was no codes I replaced it with an OEM one. I DID NOT reset the ECU after installing to rule out map issues. I let the car learn and it boosted fine to 20psi, I deemed it a success when one day on the freeway it went back to only boosting to 10psi. I then continued my research….
Vacuum Lines to BCS/Turbo
– I decided to replace the vacuum lines to the BCS, turbo, wastegate with an OEM kit from the dealer including the restrictor pill. Again, the same thing I did not reset the ECU as it has been boosting fine. That same day on the freeway to work only boosted to 10psi. On to the next….
Disconnect BCS lines
- I disconnected the BCS lines to see if the wastegate actuator is going. It consistently boosted past 10psi meaning that it could not be the actuator.
OTS Stage 2 91oct Map
– I flashed a OTS stage 2 map from www.osecuroms.org
to rule out a tune/map issue. It was fine for a few miles but as it learned it went back to boosting to 10psi.
- I replaced the knock sensor with a brand new OEM one thinking it was false knock or the sensor starting to fail and picking up other frequency’s thinking it is knock. Drove fine for a few miles and then the same day only boosted to 10psi.
What I have not done
Compression/Leak down Test
Grimmspeed BCS + Tune
Email/call other tuners/shops to discuss issue
Return to Stock
fix up pipe rattle (false knock?)
I have run out of ideas and have been extremely frustrating; it’s like driving half a STi. I am asking for your help or any suggestions that may lead to a solution. I will post logs and screenshots of learning view later and will post links from threads that have similar issues below. I will also cross post in IWSTI and the RomRaider Forums along with the 2.5 forum (MODS please let me know if cross posting is inappropriate and I will delete it)
I appreciate your help in advance and encourage any tuners/professionals to respond. also feel free to call or email me to discuss as well if its easier. PM me for info
(For you reddit'ers) TL;DR
06 STi will intermittently go to wastegate boost only 10psi, replaced several parts. Problem still prevails. Looking for solution.