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MBC for boost leak fix

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  • MBC for boost leak fix

    Hi there, I'm new to fiat and the 1.4 multiair. I've been reading a bit on the pressure bleed used to purge the charcoal canister, seems that the best current solution out there is an N/O solenoid on a pressure sensor. My question is, has anyone tried using a Ball and Spring Type Boost Controller inline with the hi pressure line feeding the tee?

    I may give this a shot (picture): introduce a second spring to keep the valve normally open, and the MBC portion should close on a desired pressure.
    Click image for larger version  Name:	boost%20controller%205.jpg Views:	1 Size:	217.1 KB ID:	1921
    Last edited by romanoaf; 01-29-2019, 10:40 AM.

  • #2
    this method might require a custom valve- the MBC solution likely doesn't seal on the stem. I'm going to try to develop a normally open pre-loaded check valve for this application. currently that type of valve looks like it only exists in medical applications.


    • #3
      Charcoal canister is for fuel vapor re-circulation for emissions purposes. What is considered boost leak is fuel gases that have been purified by the charcoal canister being reintroduced into the intake of the engine.


      • #4
        Understood, however from my understanding, the vapours are “pushed” with hi pressure air from the other side of the intake through an ejection tee (Venturi tee), this is the “pressure bleed” I’m talking about.

        Good source:


        • #5
          Originally posted by JustBob View Post
          Charcoal canister is for fuel vapor re-circulation for emissions purposes. What is considered boost leak is fuel gases that have been purified by the charcoal canister being reintroduced into the intake of the engine.
          Thats not the boost leak on the multiair turbo. The boost leak is that there is a pipe coming off the cold side charge pipe that leads straight back to the inlet of the intake pre turbo. The purpose to is to pull the eval gases with it with the use of the inline T fitting. But inturn causing boost to be bled off or '''leaked'.


          • #6
            I've found a couple pneumatically actuated valves that look promising, and have ordered one to test ($20 ebay). Siemens powermite- used in HVAC applications, but the proper config checks all the boxes so far- N/O Pneumatically actuated- options for 3-8psi, 8-13psi and 10-15psi- I like the 8-13 option as its likely a progressive close and wont seal entirely until 10-12psi.

            There are a lot of these types of valves out there, but most require pressure differential to activate, and/or are made for high pressure applications.
            Click image for larger version

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            • #7
              Proof of concept-

              Works well enough, not a perfect seal. I may try a smaller valve. In practice, the valve actuation will probably run off the manifold without the use of tees.


              • #8
                It's my professional opinion that that will work. If you can set it to close at 12psi, it's a absolute certainly that it will work. I the video it appears to be set to 5psi, and I'm about 70% sure that will be fine.

                I want to point out that 7 years after the introduction of this car, there have been many attempts at making a decent boost leak fix. At this point I think we can say that the only type that has been 100% successful, meaning stops 100% of the leak with zero chance of a CEL is a controllable type that closes above a certain boost level. It appears that this one will do that.

                In the case of the 124, our solution has been to include a slightly more restrictive venturi with our V2 and V4 intakes. That blocks so much of the leak, that we decided there wasn't enough room for improvement to justify further expense or complexity. The downside is that about 1 in 10 cars is a little more sensitive than normal and we have to send out a larger venturi to prevent a CEL, but again, that's only about 1 in 10.



                • #9
                  Thanks Greg, I’ve owned the car for about a month, and have read as much as I can on the issues and potential fixes, the HPSI fix was the most comprehensive. I wanted something that I could introduce inline, with as little modification as possible.
                  It closes fully right now at 8psi, in the video though, the guage I’m pointing at bleeds off too fast to show. But I can also modulate with an MBC if need be.
                  im not fully happy with it yet, but this is a $20 solution. I’m going to try and find a smaller valve that can be tucked away easily.
                  Last edited by romanoaf; 02-06-2019, 08:00 AM.