Low Boost Problem
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This is a discussion on Low Boost Problem within the General Maintenance, Troubleshooting & Accidents. forums, part of the Tech & Modifying & General Repairs category; Ok. A little insight of the problem in hand. Myself and a mate replaced the stock TD04 on my '02 ...

  1. #1
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    Thumbs down Low Boost Problem

    Ok. A little insight of the problem in hand.

    Myself and a mate replaced the stock TD04 on my '02 bugeye with the same turbo, just less K's as the previous was creating a large whine, and as I suspected, yes, it was pretty much screwed.

    However after replacing everything, getting everything back in, and starting the car up and going for a run, it's only running 8psi, substantially lower than stock boost.

    I'm not entirely sure of what the problem is, so I thought I would ask other's opinions.

    I used the stock gaskets, and as far as I know, there aren't any leaks coming from them.

    I've tried resetting the ECU thinking the car could be in limp mode, however to no avail.

    Any help is appreciated.

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  3. #2
    Sammich Makin' Pwincess wrxtreme06's Avatar
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    what are you using to monitor your boost? what gear were you in while observing boost?

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    Registered User EvoEatr's Avatar
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    So its the same exact turbo just a lower mileage unit?..do you know if the replacement turbo was modded at all such as adjustment of the waste gate actuator arm or anything?...How many miles are on the replacement turbo? If I where you I would def go over everything and make sure all vacuum/intake tubes/lines are secured and attached properly....depending on the year of the vehicle... take a peek here... How Subaru's Factory Boost Control System Works v1[1] 01

  5. #4
    Admiral Ackbar the 1st mycologist's Avatar
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    ^+1

    Sounds like it is running on wastegate spring pressure and the BCS isn't hooked up right or something.
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  6. #5
    Moderator Donkey's Avatar
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    You absolutely have to reuse the factory turbo lines or make sure you remove the pill and replace it in the new lines.



    "The factory boost control system bleeds pressure away from the wastegate actuator to the intake or turbo inlet pipe. With this device set at 0% wastegate
    duty cycle through the ECM calibration, all of the air pressure generated at the compressor housing will be applied to the wastegate actuator forcing the
    wastegate valve to fully open. When the wastegate actuator is fully open, the vehicle will run mechanical boost pressure which can be anything from 7-
    11psi on original equipment manufacturer (OEM) turbochargers. When this device is programmed to 100% wastegate duty cycle through the ECM
    calibration, all of the air pressure generated at the compressor housing will be allowed to by-pass to the wastegate actuator allowing the wastegate valve to
    close. The flow is limited by the size of the hole in the restrictor pill located in the first vacuum line attached to the turbo compressor housing. "

    "The middle of this restrictor pill has a lengthwise hole precisely machined to a certain
    specification so that it works with the factory wastegate actuator and the wastegate duty cycle settings in the stock ECU. The size of this center hole can be
    changed in order to mechanically assist boost control.
    A smaller diameter hole in the center of the brass restrictor pill will have a higher tendency to create boost spike in the system and require less wastegate
    duty cycle to run higher boost. The larger the diameter hole in the center of the restrictor pill, the less chance the boost control system will boost spike and
    greater wastegate duty cycle will need to run in order to produce higher boost. If you have a stock turbo and are running an AccessPORT map, you have no
    reason to modify your restrictor pill. If you have installed a new turbocharger and you are using the stock boost control system to tune boost, please verify
    that the vacuum line coming off the turbo compressor housing (prior to the T-fitting) contains a restrictor pill with a hole machined in the center of the pill
    ."

    Resident Adviser @ WTF Tuning, LLC
    2002 FORESTER S
    1998 FORESTER S




  7. #6
    Registered User Poohbear's Avatar
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    Don the 09+ have two pills?
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  8. #7
    Moderator Donkey's Avatar
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    Have you found two pills? I think they do. One in the wastegate line and on in the compressor line. Different sizes.
    Last edited by Donkey; 02-15-2010 at 08:22 AM.
    Resident Adviser @ WTF Tuning, LLC
    2002 FORESTER S
    1998 FORESTER S




  9. #8
    Registered User Poohbear's Avatar
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    I was told this over at romraider... I haven't personally looked. I was told people have better luck controlling boost with a tune when they remove one of the pills..

    But like I said i haven't personally looked...

    After all the dealer seems to watch me on these forums so I will not be doing any modding or flashing of my car what so ever... Everything I ask is purely for research and my curiosity. After all I would not like to void my warranty....
    Your vehicle is an extension of your skill as a driver, not a substitute for it.

    Stink-Eye Mob Member #21
    08+ Gauge install DIY
    Turn off your seat belt chime

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