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Thread: Turbo runs fine but 0psi read at intake manifold

  1. #1
    Forum Member 1st year Apprentice
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    Default Turbo runs fine but 0psi read at intake manifold

    Hi all,

    I am currently running a 4th gen 3SGTE A/T. Stock exhaust/intake manifold, stock turbo and wastegate. Only custom piping and intercooler with HKS BOV.
    Car was running fine, at 0.5bar (7 PSI) more or less, a nice engine with nice power.

    But suddenly, one day, my boost gauge was reading around 0-0.2 bar (0-3 PSI), and feel like Naturally Aspirated. Car runs fine (around 150 HP), but without turbo extra power.

    I have checked the wastegate (opens at around 0.5-0.7 bar / 7-10psi), I have removed the BOV to ensure this point. I have checked leaks from air intake to throttle body (closed) and it holds 1 bar (14 psi), there are some clamps I have replaced after this to improve the sealing, but no improvements in performance. I have check vacuum leaks from the intake manifold (boost gauge vacuum, bov vacuum line, brake line...), but no leaks.

    When I run the car and hold gas, turbo goes to 0.5 bar (7 psi) in wastegate gauge, and it sounds fine. But in the intake manifold, I only can read 0-0.2bar (0-3psi). The gauge is OK because I have some of them and I have changed them to ensure it.

    I think there is a easy problem or leak but I have spend many headache days with this.

    I hope any can give me any idea.

    Thanks in advance.

    Enviado desde mi H8216 mediante Tapatalk

  2. #2
    Junior Member Backyard Mechanic jondee86's Avatar
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    Default Re: Turbo runs fine but 0psi read at intake manifold

    I'm not a turbo guy so I can't understand how you can have 7psi in one part of the system and
    only 2-3psi in another part ?? But leaving that aside, as I understand it, to get 7psi in the manifold
    there has to be resistance to flow. That resistance is the turbo trying to push air into a cylinder
    when the inlet valve is open and the outlet valve is closed. If for some reason, the outlet valve is
    open at the same time as the inlet valve, then the charge air will pass right thru the cylinder and
    the resistance to flow (=turbo pressure) will be less.

    So my suggestion would be to check your cam timing and VVT operation to see if for some reason
    you have a lot more valve overlap than you had before.

    Cheers... jondee86

    EDIT: Disregard the above. This answer only addresses a situation where a turbo cannot make boost.
    Last edited by jondee86; 06-07-2021 at 01:00 PM.

  3. #3
    ethanol sniffing Backyard Mechanic adamaw11's Avatar
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    Default Re: Turbo runs fine but 0psi read at intake manifold

    what if there was a restriction somewhere between turbo outlet and the intake manifold where the pressure drops, rather than a leak? test for pressure at various points, after intercooler etc, to eliminate that possibility?

  4. #4
    Junior Member Backyard Mechanic jondee86's Avatar
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    Default Re: Turbo runs fine but 0psi read at intake manifold

    Quote Originally Posted by adamaw11 View Post
    What if there was a restriction somewhere between turbo outlet and the intake manifold
    where the pressure drops, rather than a leak?
    This actually makes more sense than my suggestion If there is less resistance at the engine,
    then the turbo should not be able to build a lot more pressure at the turbo than it does at the
    engine. The only difference would be the pressure drop thru the intercooler and charge ducting.
    But if there was an obstruction, for example a rag stuffed into the intercooler, there would be a
    pressure drop across the obstruction that would lower the pressure available at the engine.

    Cheers... jondee86

  5. #5
    Junior Member Automotive Encyclopaedia
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    Default Re: Turbo runs fine but 0psi read at intake manifold

    What was done to it last, before the power loss: adjustments, maint, replacements, mods, collision... ?
    'I've scrapped better.' John stated when asked about the car by the guy with the silver tipped cowboy boots!

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