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Old 12-30-2006, 10:17 AM   #1
Scooby Newbie
Member#: 66808
Join Date: Jul 2004
2004 WRX STi
WR Blue w Gold

Question 03 WRX with boost oscillating problem

Hello everyone, here are the details of the problem that my friend is facing:
For the past few months now my friend has had a problem on 3rd gear and up; once in 3rd gear, the turbo starts oscillating back and forth between ~10.5 and ~15 psi. I have searched this forum and a couple of other sites with regards to this issue (it seems to be an old issue) and haven’t found a solution to this problem. We have already tried the following (as other people have suggested):
1. swap the BPV for another stock one (brand new)
2. swap the stock electronic boost controller for another (brand new)
3. checked and changed all the hoses for brand new silicon hoses (with a brand new restrictor pill purchased at the dealer)
4. took it to Subaru dealer where they tested the car’s ECU and everything registered fine

We installed a manual boost controller to rule out the possibility of a sensor that might be screwed; when shifting into third, boost increases drastically to ~17 psi and backs down immediately to whatever preset setting we put it to (while testing the max that we dialed the manual boost controller was 11 psi!), sounds like boost spike doesn’t it?

The service manager (a good friend of ours) at the dealer gave us the phone number of a guy that specializes in Subaru’s and he ran some tests, he put the waste gate actuator under vacuum and found that it has a slow leak…

My questions would be: is it normal for the actuator to have a slow leak under vacuum?

Anything else that we need to test?

Any help/info/guidance with regards to this matter is greatly appreciated it as this problem is driving us insane with all the testing we have done…

His mods are as follows: snorkel delete, STi up-pipe, BPM 3” TBE with cat. The car has been working fine with these mods for the past 3 years and now that the engine has hit ~60K miles its been having this issue.

Thank you again for any suggestions/advice on this matter.
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X_Driver is offline   Reply With Quote
Old 12-30-2006, 01:40 PM   #2
*** Banned ***
Member#: 24038
Join Date: Sep 2002
Chapter/Region: South East
Location: Godspeed Cale...

Yeah, definately sounds like a leak....if its from the WG, just replace that...

If its not caused by the WG, there's definately a leak somewhere close by. You guys already checked all of the hoses form your post. You should be able to pick up an used WG on here pretty cheaply.

A second option would be for your friend to sell me his BPM exhaust, epecially if the muffler is a TT>
REX8 is offline   Reply With Quote
Old 12-30-2006, 02:18 PM   #3
Scooby Guru
Member#: 60324
Join Date: Apr 2004
Location: a pillow.

here's a way to check the WG:

run a hose from the compressor nipple directly to the WG, bypassing the OEM BCS. this will put direct pressure on your WG, you should have rock steady boost, right at the WG level (around 11 psi IIRC). I'm sure you can find out what the stock WG pressure is with a quick search... it's been so long since i've had the stock turbo i honestly don't remember.

if the boost oscilates in this fasion, the WG is done.

your options then are, replace the WG, replace the whole turbo with a used one (they can had for like 100$, and new AM wastegates are like 75), or get a bigger turbo and upgrade.
hondaeater69 is offline   Reply With Quote
Old 01-01-2007, 10:01 AM   #4
Scooby Newbie
Member#: 66808
Join Date: Jul 2004
2004 WRX STi
WR Blue w Gold

Thumbs up thank you....

Thanks for the replies, we will test WG actuator that way and see what happens...

and Happy New Year everyone!!
X_Driver is offline   Reply With Quote
Old 01-01-2007, 10:55 AM   #5
Scooby Newbie
Member#: 69636
Join Date: Sep 2004
Chapter/Region: MAIC
Location: Westminster, MD
2002 Wrx
Sedona Red


I have had the same problem with mine in 3rd, 4th and 5th but it stops after 4000 rpm. Could the wastegate be the culprit also? The boost never oscillated like that until after I had a protune.
MdWRX is offline   Reply With Quote

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