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  1. #1
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    underboosting issues

    hey guys, hoping for some insight.

    Ive noticed that my car cant hit more than 17 psi in the midrange regardless of target, and overall seems to be down 2 psi or so overall.

    I checked vacuum to the wastegates and solenoids by teeing in a gauge with JB4 lagfix set to 100 and read out 22 inches of vacuum.

    sprayed carb cleaner on all the lines and found no signs of a leak anywhere.

    only thing left I can think of are tired wastegates? has anyone ever adjusted the rod to resolve such an issue?

    will post logs with an example of this later.

    running JB4 + BT flash combo, FBO + meth.

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    Is your DC maxed?

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    The 135i I'm working on is underboosting too. I'm putting it on a lift tomorrow to see if I can find anything. Does it do it at stock boost levels?
    2011 335is DCT, JB4 + MHD BEF, stage 2 LPFP, e50 + 50/50 meth, FBO, MT ET Streets when needed


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    Click here to enlarge Originally Posted by E90Company Click here to enlarge
    Is your DC maxed?
    its close to maxed on the JB4 which is logged as PWM. ill post the log later.

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    Click here to enlarge Originally Posted by bigdnno98 Click here to enlarge
    The 135i I'm working on is underboosting too. I'm putting it on a lift tomorrow to see if I can find anything. Does it do it at stock boost levels?

    nope. even map 2 which is 14.5 psi it has no problems

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    I'm gonna try that out tomorrow before I put it on the lift and see if it has problems with maps 1,2 or 4. Mine starts out way under target, 3psi but eventually catches up. Hell, you saw the logs. Is yours always under target or does it catch up eventually?
    2011 335is DCT, JB4 + MHD BEF, stage 2 LPFP, e50 + 50/50 meth, FBO, MT ET Streets when needed


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    Click here to enlarge Originally Posted by bigdnno98 Click here to enlarge
    I'm gonna try that out tomorrow before I put it on the lift and see if it has problems with maps 1,2 or 4. Mine starts out way under target, 3psi but eventually catches up. Hell, you saw the logs. Is yours always under target or does it catch up eventually?
    it'll catch up in 4th. assuming youre running a JB4 ISO as well?

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    Yup. I was running latest software. I loaded up an older firmware but it still did it. I may put a g4 back on and pull some logs.
    2011 335is DCT, JB4 + MHD BEF, stage 2 LPFP, e50 + 50/50 meth, FBO, MT ET Streets when needed


  9. #9
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    Click here to enlarge Originally Posted by themyst Click here to enlarge
    it'll catch up in 4th. assuming youre running a JB4 ISO as well?
    when i was logging my car with zeel a week or two ago, he noticed in 3rd gear i was underboosting by about 1 psi. in 4th i was dead on with my target. i chalk it up to boost solenoids or wastegates getting weak. 85k miles on my original turbos with lots of abuse lol.
    2008 e92 335i: JB4 G5 ISO/BMS back end flash, fbo, e85, inlets, Rb turbos, level 10 valve body + converter, water/methanol.....and a lot more....

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    Due to load, DC in the higher gears will always be lower to meet target.
    Whats the DC at 100 lag fix? For example 22" at 100% DC is too low, but at 70% prob ok.
    To check the WGs you can check the rear easily... Use your hand to find full closed, then put a vac pump on it to find vac to reach that point. Should be 7ish.
    You can check the front also but very difficult and more visual guessing. I don't remember well though.
    When playing with vac pump and WGs you can good idea if they're moving smoothly, catching, etc.
    check boost solenoids at idle... without current some hold vac, some don't... Doesn't mean anything.

    Put up a log... If its JB you'll have to dumb down how to read pwm for me though.

  11. #11
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    Click here to enlarge Originally Posted by JoshBoody Click here to enlarge
    Due to load, DC in the higher gears will always be lower to meet target.
    Whats the DC at 100 lag fix? For example 22" at 100% DC is too low, but at 70% prob ok.
    To check the WGs you can check the rear easily... Use your hand to find full closed, then put a vac pump on it to find vac to reach that point. Should be 7ish.
    You can check the front also but very difficult and more visual guessing. I don't remember well though.
    When playing with vac pump and WGs you can good idea if they're moving smoothly, catching, etc.
    check boost solenoids at idle... without current some hold vac, some don't... Doesn't mean anything.

    Put up a log... If its JB you'll have to dumb down how to read pwm for me though.
    Don't know what PWM translates to in terms of WGDC flash side, but PWM 86 = 22 inches of vacuum, at least on my car. I would think 100% WGDC is around 26 inches, no?

    Click here to enlarge

  12. #12
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    Yeah 26"ish from the pump. 22" for 86% seems a little low, but maybe not enough to under boost like you are... check the plumbing and DVs, o-ring on the CP. Just have to thoroughly confirm each system is working correctly.

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