Strange boost problem?
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This is a discussion on Strange boost problem? within the General Maintenance, Troubleshooting & Accidents. forums, part of the Tech & Modifying & General Repairs category; Hey guys today I dropped 3rd and my boost gauge warning went off and I was boosting almost 25 psi, ...

  1. #1
    Registered User tsize4's Avatar
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    Strange boost problem?

    Hey guys today I dropped 3rd and my boost gauge warning went off and I was boosting almost 25 psi, I am tuned for 20 psi open source. Now 1st-3rd I'm hitting 20 and 4th and 5th I'm hitting 20 and dropping to about 15. Was thinking it was a boost leak buy not with over boost conditions? It's leaving me scratching my head.

    04 wrx, vf39, Fmic, id750 injectors, open source tune,
    Thank for any help

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    How are you controlling boost? MBC?
    You're holding 20 pounds with no issues in all other gears before 4th & 5th?

  4. #3
    Registered User tsize4's Avatar
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    Sorry forgot to add that. Turn in concepts said that my stock boost control solenoid is bad so they tuned it with an aem solenoid. Anyways I am using a mbc . Yesterday I took the mbc off and pulled both lines off to get to a harness, if I reversed the lines to the boost controller will it make a difference?

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    Yes, it will make a big difference, you would definetely be able to tell.
    That is not your issue though.
    So, are those the only 2 gears you see a difference in?
    You're positive this wasn't happening before?

  6. #5
    Registered User tsize4's Avatar
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    Quote Originally Posted by CalebPatton View Post
    Yes, it will make a big difference, you would definetely be able to tell.
    That is not your issue though.
    So, are those the only 2 gears you see a difference in?
    You're positive this wasn't happening before?
    Yeah as far as I can tell it's those gears. But it has always held 20 no matter what.

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    Registered User tsize4's Avatar
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    Maybe a problem with the waste gate actuator?

  8. #7
    Registered User EndlessSea's Avatar
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    wate gate seems the most logical place to start if you're using an MBC. maybe it got temporarily stuck closed? its possible although unlikely. it only happened once and then back to 100% normal?
    2013 wrx sedan(saving up for a 2015 STI)

    Previous faist cars: '05 Mustang GT '02 RSX-S, '91 SR20 240sx, '85 300zx turbo

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    Honestly, the only thing I can think of to do is check everywhere for a boost leak, then log your car & unless you are good at reading the data, have your tuner look at it.
    Your issue has me stumped because its only doing it in those 2 gears & holds fine in others.

  10. #9
    OMG WTF MainFrame's Avatar
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    I would consider holding 20 to redline an issue, and the current behavior functioning as it should. Your turbo isn't large enough to efficiently push 20psi at 7000rpm on a 2.5L engine.

  11. #10
    Registered User tsize4's Avatar
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    Sorry guys, im tuned to drop of to 15 psi at redline . But oddly enought it has happened more that once . It has consistently overboosting in 3rd and underboosting in 4-5. Weird

  12. #11
    Registered User tsize4's Avatar
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    Update: lines running from inlet side of the turbo and from the wastegate actuator to the mbc were switched and it solved the problem. Thanks for the help dudes

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