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Thread: Help me! EJ208 not boosting properly.

  1. #1
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    Aug 2023
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    Exclamation Help me! EJ208 not boosting properly.

    Alright, I've recently acquired a BH5A Legacy with 95k on it for what I think was a pretty good deal. Reason being is that it isn't boosting properly, it sounds like a has pretty substantial boost leak. Previous owner is/was under the impression that the secondary turbo has given up. I'm not so sure thats the issue although it is possible and the primary is just blowing air through a siezed or real bad secondary.

    The car only makes about 5-6PSI. The VOD does not seem to occur unless I shift into it, then the car will drop to 1-2PSI before recovering back to 5-6PSI. There is some light oil residue in the charge pipes from both turbos, both appear normal from my experience with turbo engines.

    There is no check engine light.

    I've checked all vacuum lines, including the BBOD for proper routing against the diagrams found on this forum and also for obvious leaks, visually there is nothing wrong with them, they are routed correctly and are not brittle. Currently trying to find somewhere that can smoke test it or make something that I can make work myself, I don't have access to an air compressor so that might be tough...

    I do have some confusion around the lines from the primary turbo/wastegaste to the boost solenoid and the aftermarket GoFastBits BOV. There was a disconnected vacuum line there off the primary turbo intake pipe but no change after reconnecting. I think I could be looking at the line 10 mod but I'm not certain and the car was previously boosting correctly according to the previous owner so I haven't mucked with them.

    I have a line on some replacement turbos (VF25/VF27) current primary is a VF31 and haven't had time to get a read on what the secondary is. Replacing what I have with the 25/27 will be a bolt on operation and won't cause any issues correct?

    The car does seem to have a small exhaust leak, I can smell it but can't seem to locate it. Any suggestions on where I could find a replacement set of TT headers and all the associated gaskets for doing a header/turbo replacement would be much appreciated as I am struggling.

    Also doing the timing belt/idlers and water pump, waiting to hear back on a kit for that.

    What I'm looking to gain from this post is confirmation that I'm at least on the right track. Or if there are any suggestions on what lines/solenoids deserve a closer inspection, I'm listening!

  2. #2
    New User
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    Mar 2015
    Sydney, Aus
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    step 1 - find the boost leak.

    Do a standard (smoke, etc) boost leak check first - it may be something simple like the shitty plastic intercooler inlet pipes or a loose clamp. I recommend throwing those pipes away, and using standard silicon bends of the appropriate sizes. You'll get better spool.

    If its not as audible as a 'usual' boost leak, two TT-specific things to check.

    1/ the IACV (intake air control valve) on the secondary. That's the big throttle-body like flap plate connected to the intercooler under the driver's side. That'll cause the primary boost to leak back through the secondary when in primary-only turbo mode.

    2/ the secondary PRV (pressure relief valve). That's a weird little plastic diaphragm valve under an upside-down u-shaped bit of pipe, located between the secondary outlet and intercooler. It'll cause secondary boost to leak back into the intake (post MAF). It's basically a bypass valve which is opened up during secondary spool.

    number 2/ wouldn't cause boost drop when on primary.

    6psi is almost (but not quite) wastegate pressure (~9psi?) - so make sure your wastegate is plumbed up correctly.

    Start here. Original link is dead, but the clubsub quote is still alive:

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