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Turbo actuator vacuum piping

Discussion in 'A4/A4 cabriolet/S4 forum(B6 chassis)' started by Gaz!, Apr 1, 2013.

  1. Gaz!
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    Gaz! Member

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    [Apr 1, 2013]
    Excuse me if this has been covered before, my Audi (1.9 tdi, 130 sport) is my casual run around, I service it but don't know the ins and outs of it.

    I've got a Defender that I have been playing with and thought I'd do a couple of bits to the A4. I'm thinking of fitting a grainger valve to up the boost slightly, obviously would fit a boost gauge to keep an eye on any spiking or creep. I have had a look today and the vacuum pipe that connects to the turbo actuator doesn't connect to the inlet manifold, it goes to an electric valve? What on earth is this??? I'm used to the actuator opening, as it feels the pressure at the manifold.

    Couple of questions.

    What is this valve, and what seems like an accumulator next to it also taking a feed from it?

    Can I pop a grainger valve in between the valve and the actuator? Would this work? As in delaying the opening of the waist gate. That saying that the actuator works on pressure, or is it vacuum?

    Or could I just tap a take off into the manifold and run a pipe to the actuator? Then plug where it came from this valve thing?

    Any help would be great.
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  3. stu_m
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    stu_m Active Member VCDS Map User

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    [Apr 1, 2013]
    the valve is called the N75 valve it controls all the actuation of the turbo

    not sure on this grainger valve thing never had any experience with them

    how do they give extra boost exactly? you may run in to trouble with the car going it to limp home mode and registering an overboost
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  4. Gaz!
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    Gaz! Member

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    [Apr 1, 2013]
    It's an MBC, manual boost controller, it interrupts the boost pressure felt at the actuator. It's basically a spring with a ball bearing that can be screwed in or out, this will delay the actuator opening allowing a little extra boost to build. As long as a boost gauge is employed to keep an eye on boost levels then its not a problem.

    I use an EBC, electronic boost controller on my MR2, great way to control from inside the cabin.

    Just need to know how I go about making this work with the N75.
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  5. Gaz!
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    Gaz! Member

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    [Apr 1, 2013]
    I've also been reading that the N75 can be adjusted, perhaps this could act as an MBC?
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  6. Audi Doodah
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    Audi Doodah Active Member

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    [Apr 2, 2013]
    If you want to up your boost slightly, get a remap!

    Not familiar with the grainger valve thingy but seems a lot of effort only for the car's ECU to detect an overboost and go into limp mode before you can 'manually' adjust your boost
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  7. Gaz!
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    Gaz! Member

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    [Apr 2, 2013]
    Well today took the EGR and manifold off for a good clean. Followed the vacuum pipes around and took a look at the N75. Not anywhere on it can I see where it is adjustable.

    However noticed the vacuum pump on the back of the head, obviously this is the source of the vacuum as it supplies the brake servo, also doubles up as the fuel pump I think?

    Is the turbo diaphragm controlled by vacuum and not boost? That would be a problem.

    Anyone?
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  8. Audi Doodah
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    Audi Doodah Active Member

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    [Apr 2, 2013]
    Yes, turbo actuator is controlled by the N75 valve. Boost pressure is measured by the MAP sensor just before the EGR valve.
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  9. Gaz!
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    Gaz! Member

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    [Apr 2, 2013]
    Yeah I see. What I mean is, the diaphragm is controlled by vacuum from the N75, it doesn't receive it's own boost pressure to open the waistgate at the actuator spring pressure.
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  10. Audi Doodah
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    Audi Doodah Active Member

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    [Apr 2, 2013]
    Nope. It's a VNT turbo so no wastegate. Actuator opens and closes vanes within the turbo to regulate boost
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