Welcome to the North American Subaru Impreza Owners Club Tuesday October 16, 2018
Home Forums WikiNASIOC Products Store Modifications Upgrade Garage
Go Back   NASIOC > NASIOC Technical > Factory 2.5L Turbo Powertrain (EJ Series Factory 2.5L Turbo)

Welcome to NASIOC - The world's largest online community for Subaru enthusiasts!
Welcome to the NASIOC.com Subaru forum.

You are currently viewing our forum as a guest, which gives you limited access to view most discussions and access our other features. By joining our community, free of charge, you will have access to post topics, communicate privately with other members (PM), respond to polls, upload content and access many other special features. Registration is free, fast and simple, so please join our community today!

If you have any problems with the registration process or your account login, please contact us.
* Registered users of the site do not see these ads. 
Thread Tools Display Modes
Old 05-19-2017, 02:55 PM   #1
Scooby Newbie
Member#: 466935
Join Date: May 2017
Default Help!! Boost leak found. Bypass valve leaks after 6 psi. vid inside.

Been chasing an issue with not hitting boost target and tapering off to fast. Did a boost leak test without a boost gauge a couple of weeks ago and it seemed to be ok as I couldn't find any external leaks with soapy water. Didn't know how much boost I was putting in but it was obviously less than 6 psi as I found out today. Took off the top mount intercooler with the bypass valve and y pipe and throttle body couplers still attached. Put my homemade boost tester in the TB coupler and blocked off the y pipe hose end that goes on the turbo. I installed a boost gauge on my tester this time to see what was going on. Wouldn't boost to over 6 psi. from 6 psi down it would hold the boost forever until I would let it out. sprayed soapy water in the bypass valve and behold, bubbles galore. I can push down on the internal valve to help it make around 9 psi but it still slightly leaks and as soon as i let off of it with my hand it blows of back down to 6 psi.

How much boost should a stock bypass valve hold before leaking? What are my options here? Crush the top of the BP valve? Get a used wrx one? get a used sti one? Do the mod that plugs that small hole and drill out another so it holds more?

* Registered users of the site do not see these ads.
RexBoostRally is offline   Reply With Quote
Sponsored Links
* Registered users of the site do not see these ads.
Old 05-20-2017, 08:17 AM   #2
Scooby Newbie
Member#: 305468
Join Date: Dec 2011
Chapter/Region: Tri-State
Location: Oradell NJ
2012 IAG Built STi


You didnt have the boost/vaacume line connected. When under boost the pressure increases on the diagram to keep it shut. Without the line connected the diaphragm only has atmospheric pressure to help it stay closed.
12pbsti is offline   Reply With Quote
Old 05-20-2017, 11:26 AM   #3
Scooby Specialist
Member#: 298403
Join Date: Oct 2011
Chapter/Region: W. Canada
Location: Alberta, Canada
2008 WRX Premium
Spark Silver


+1, you need pressure on the vacuum nipple side to keep the valve closed. The spring only holds to around 6psi, if I'm not mistaken, but that pressure is variable depending on what spring/valve your have installed. When boost is applied to the top side of the valve, pressure is equalized and the spring won't move, allowing you to build higher boost pressure in the intake.

Go Fast Brett explains it in more detail...
viper_crazy is offline   Reply With Quote
Old 05-20-2017, 11:43 AM   #4
Scooby Newbie
Member#: 466935
Join Date: May 2017

Ahhh that makes sense. Guess the only way to test it is leave everything still on the car but pop off the bypass valve elbow to see down in there with its vacuum/boost line still hooked up. No way to give it equal boost on top with it off the car using the tester like i did. Ughhhhhh. Thought i had it figured out. Im about to just pull the wastegate line off and go full boost into a tree lol
RexBoostRally is offline   Reply With Quote

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump

All times are GMT -4. The time now is 03:54 AM.

Powered by vBulletin® Version 3.7.0
Copyright ©2000 - 2018, Jelsoft Enterprises Ltd.
Powered by Searchlight © 2018 Axivo Inc.
Copyright ©1999 - 2017, North American Subaru Impreza Owners Club, Inc.