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Old 05-19-2017, 02:55 PM   #1
RexBoostRally
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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?

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Old 05-20-2017, 08:17 AM   #2
12pbsti
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Member#: 305468
Join Date: Dec 2011
Chapter/Region: Tri-State
Location: Oradell NJ
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2012 IAG Built STi
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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.
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Old 05-20-2017, 11:26 AM   #3
viper_crazy
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Chapter/Region: W. Canada
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2008 WRX Premium
Spark Silver

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+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...
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Old 05-20-2017, 11:43 AM   #4
RexBoostRally
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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
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