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Discussion Starter · #1 ·
Hello all, my 08 wrx has started to overboost. About two months or so ago i installed a autometer boost gauge. Max boost was 11psi, I checked online and saw it was about right for my year. A couple of weeks ago i took apart my dash to fix the infamous pedal assembly spot weld failure. While working on the dash i kinked the tube to the boost gauge. So i left it not hooked up till i got a new compression fitting. Since it was not connected a sound came about while downshifting. It sounds like a loose heatshield, or a small exhaust leak at a gasket (im thinking unrelated to boost problem but want to give all details) Finally i re hooked up the gauge. Boost went from holding steady at 11 to peaking to 15psi. If i let off and get back on it, it goes to 8 then up to normal. If i get on the throttle again it goes right up to 11psi. ( i stayed off boost after it hit 15psi)

Fast forward to today, i looked up some steps to check the wastegate and BCS. I applied pressure and vacuum to the wasegate actuator. Vacuum i did 25hg and in about5 minutes it read 23hg. For pressure i did 25psi and it held about the same for 5 minutes. So to me the actuator is good, right?

The BCS clicks when 12v is applied to it. I cleaned it and my MAF with MAF cleaner. Replaced vac lines on the T fitting the BCS and wastegate connect. Now boost peaks at 20psi :whoa:

Any ideas? Maybe my BCS is junk even though it clicks? Wastegate actuator opens at 15psi when i did my testing. I would like to fix it rather then throw parts at it. My mods are: invidia N1 cat back, k&n CAI (both came on the car when i got it in march and dont know if it was tuned for these mods) I dont know anyone who has the same car to swap the BCS either. If you guys and gals need more info just ask. TIA
 

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First, I would stop driving it until you verify a tune for the equipment on the car. That could be part of the overboost issue.

Under what situation are you getting the overboost. It's super common to cause it with wot acceleration in 4th or 5th gears at low speed. I would also check the waste gate and make sure it's operating properly

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Discussion Starter · #3 ·
It never over boosted when I first got the car until recently.
When it does it's usually when I'm full throttle, in anygear mid to high rpm.
But it's not every time, it randomly happens.

First, I would stop driving it until you verify a tune for the equipment on the car. That could be part of the overboost issue.

Under what situation are you getting the overboost. It's super common to cause it with wot acceleration in 4th or 5th gears at low speed. I would also check the waste gate and make sure it's operating properly

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It never over boosted when I first got the car until recently.
When it does it's usually when I'm full throttle, in anygear mid to high rpm.
But it's not every time, it randomly happens.
Yeah those are the situations you should avoid in a turbo car. High engine load wide open throttle. The intake requires a tune. No middle ground

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Discussion Starter · #5 ·
Ok, thank you. I'll have to find a protuner in Massachusetts then. Would it be.worth it to just remove the cai and just use the stock airbox set up (performance wise)

It never over boosted when I first got the car until recently.
When it does it's usually when I'm full throttle, in anygear mid to high rpm.
But it's not every time, it randomly happens.
Yeah those are the situations you should avoid in a turbo car. High engine load wide open throttle. The intake requires a tune. No middle ground

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I think you removed the restrictor pill when you did the vac. lines.

The BCS increases boost when it is working. If it doesn't work boost falls to 8psi or so (spring pressure of the wastegate actuator).

Not worth a protune on stage 1 - just get a stock intake. The one on there is not doing anything for power anyways.
 

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Discussion Starter · #7 ·
It was overboosting before I did the vac lines. I checked for the pill but there wasn't one in the 3 lines I replaced on the T fitting. Which one is it supposed to be in? I start my search for a stock airbox set up too. Thanks!

I think you removed the restrictor pill when you did the vac. lines.

The BCS increases boost when it is working. If it doesn't work boost falls to 8psi or so (spring pressure of the wastegate actuator).

Not worth a protune on stage 1 - just get a stock intake. The one on there is not doing anything for power anyways.
 

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I thought you said it went from 15psi to 20psi, sorry if I misunderstood. Not having one would actually reduce your boost, but it may cause the spiking.

You need them though.
"The 2008+ WRX/STI has two restrictor pills. The smaller restrictor pill (the vacuum line with the pink dot) needs to go to the wastegate actuator and the larger restrictor pill (the vacuum line with the yellow dot) needs to go to the compressor housing."
https://cobbtuning.zendesk.com/hc/en-us/articles/200025204-Subaru-Restrictor-Pill-Information

Why -
https://www.cobbtuning.com/support/how-subarus-factory-boost-control-system-works-v1-09/

It is hard to tell from your description if you are seeing spikes or if it is runaway boost holding those levels. Or you aren't waiting to find out? A log here and reading the boost directly from the ECU would be a huge help.
 

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Discussion Starter · #9 ·
At first it was at 15 then 20psi after replacing the lines (previous owner I guess did too since there was no dots on the lines) must of removed the pills. On the bcs there is a yellow/clear line, looks 8mm or so, that reduces to 5/32 or 3mm I assume. This isn't stock right? I'll get the pills and the proper lines to make it right.


I thought you said it went from 15psi to 20psi, sorry if I misunderstood.

You need them though
"The 2008+ WRX/STI has two restrictor pills. The smaller restrictor pill (the vacuum line with the pink dot) needs to go to the wastegate actuator and the larger restrictor pill (the vacuum line with the yellow dot) needs to go to the compressor housing."
https://cobbtuning.zendesk.com/hc/en-us/articles/200025204-Subaru-Restrictor-Pill-Information

Why -
https://www.cobbtuning.com/support/how-subarus-factory-boost-control-system-works-v1-09/
 

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Sorry see my edit as well. No that doesn't sound stock at all.
 

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Discussion Starter · #11 ·
I need an accessport to log right? Or is there some cable and software I can use? When it reaches 15 or 20psi I let off cause I don't want to blow up my engine since its not correct (first subaru and turbo car. Usually had V8s)

Sorry see my edit as well. No that doesn't sound stock at all.
 

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Fix the lines first but -

You can log with an openport cable/laptop/free software (romraider) which is my preference. There may be other new even more affordable devices I'm not aware of. However, that cable lets you log, download the map that is on there so you can look at it and edit it even, and flash a new map. An appropriate stage I map (assuming stock airbox and exhaust) can be found for much less than a pro-tune and then you would know exactly what is on it.

Welcome to the world of the turbo flat 4. Are you sure the downpipe is stock? No other boost control, manual or electronic?


What you describe sounds like classic "boost creep" which is a PITA, but I have only heard of that from being catless (2.5l) so hopefully that is ruled out. Also that is usually from starting at low RPM high load in a high gear.
 

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Discussion Starter · #13 ·
Im pretty sure that the downpipe is stock. I should take a close look though. Only boost control is stock. Looks like one of the previous owners just slapped parts on it and never did any supporting mods for it. Its weird that it just started to happen a couple weeks ago. Now to hunt for the vacuum lines, pills, and log cable
 

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It starting a few weeks ago means something mechanical happened. You aren't showing a leak. You don't have a 3-port solenoid so the restrictor pill being gone should reduce boost.

I just read again and didn't see the part the actuator is not opening until 15psi - that sounds really really high for stock. ~8psi was normal for stock on my car ('03). If you grab it and yank on it is it opening smoothly? Being higher psi than it was tuned for will definitely cause overboost. It can be adjusted via the nut (if they still have a nut) but it sounds more like it is seizing up and sticking internally given the newness of the issue. To adjust you would loosen the tension on the actuator spring (lengthen the arm).
 

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This is an '06 but I don't think they changed it

 

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Discussion Starter · #16 ·
wastegate opens freely when i move it by hand. I been searching for the part numbers for the vac lines and pills but having a hard time. All im finding are older cars.
 

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Stick with it - you may have to call a dealer.

I think the wastegate actuator is a big problem.

When you get this right I expect it will be much more responsive at all levels and you should be able to hit much higher than 11psi safely without it running away on you. The extra power will be very noticeable going from 11psi to 16.

WTF Tuning (send PM to ej257) would likely be able to help without the intake swap as well and are very well known here.

If not these guys have a map and support for a K&N intake and can check your logs to make sure it is running well. You have to have the pills and all the other stuff right. 16.5 psi target for stage I.

2008 Wrx Stage 1
 

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Yeah that is bubba'd - just put it back to stock.

If that is opening at 15psi it is likely your actual new problem. 7-8 psi is the target unless it is purposeful and carefully tuned for.
 
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