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  1. #1
    Veteran Member Three Rings
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    can i ask a question to those of you with vcds and knowledge of vcds

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    using vcds and watching group 118 what are you guys getting for you mbar reading @ idle - last cell on the far right, boost pressure actual??
    2008 Ibis RS4....GETing tuned

  2. #2
    Veteran Member Four Rings vavJETTAw36's Avatar
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    Woodbridge, VA

    It's going to differ a bit for everyone because of temperature and how high low you idle.


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  3. #3
    Veteran Member Three Rings
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    right, but should the reading be in the negative @ idle??
    2008 Ibis RS4....GETing tuned

  4. #4
    Veteran Member Four Rings getslideways's Avatar
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    Just in case the reason you are asking is because you are confused by what appears to be a high number: keep in mind that pressure readings are factoring ACTUAL atmospheric pressure. We often consider ourselves to be at 0psi at sea level, but that's not true, we constantly have the entire weight of the atmosphere pushing down on us at all times, but we dont think about it because its what we are used to (its one contributing reason why Astronauts are usually temporarily taller after a lengthy space stint as they dont have the atmosphere and gravity pushing down on them).

    At sea level, the atmospheric pressure is ~ 14.70psi or ~1,000mbar

    The audi ECU reads pressure, INCLUDING the pressure just created by the atmosphere. So if your car was making ~15psi, it would register as 1,000mbar + the atmospheres 1000mbar and display ~2,000mbar. So just parked at sealevel with the engine off, it should still read about 1,000mbar

    If this wasnt why you were asking, then I just wasted your time and my apologies lol

  5. #5
    Veteran Member Three Rings
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    Quote Originally Posted by getslideways View Post
    Just in case the reason you are asking is because you are confused by what appears to be a high number: keep in mind that pressure readings are factoring ACTUAL atmospheric pressure. We often consider ourselves to be at 0psi at sea level, but that's not true, we constantly have the entire weight of the atmosphere pushing down on us at all times, but we dont think about it because its what we are used to (its one contributing reason why Astronauts are usually temporarily taller after a lengthy space stint as they dont have the atmosphere and gravity pushing down on them).

    At sea level, the atmospheric pressure is ~ 14.70psi or ~1,000mbar

    The audi ECU reads pressure, INCLUDING the pressure just created by the atmosphere. So if your car was making ~15psi, it would register as 1,000mbar + the atmospheres 1000mbar and display ~2,000mbar. So just parked at sealevel with the engine off, it should still read about 1,000mbar

    If this wasnt why you were asking, then I just wasted your time and my apologies lol
    hahaha no worries man, im just seeing things in actual values and trying to understand them. my car at 800 rpm was reading appx 500mbar, if how you explained it is true, then that's probably normal and I thank you for educating me!!!
    2008 Ibis RS4....GETing tuned

  6. #6
    Veteran Member Four Rings getslideways's Avatar
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    Quote Originally Posted by axnjaksn View Post
    hahaha no worries man, im just seeing things in actual values and trying to understand them. my car at 800 rpm was reading appx 500mbar, if how you explained it is true, then that's probably normal and I thank you for educating me!!!
    Glad to hear I didnt completely waste you time with my Mr. Wizard segment then lol

    If i get a chance and my VAGCOM laptop is charged i'll try to see what mine registers when running, just for some sort of reference for ya.

  7. #7
    Veteran Member Four Rings NOTORIOUS VR's Avatar
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    Toronto

    Quote Originally Posted by axnjaksn View Post
    hahaha no worries man, im just seeing things in actual values and trying to understand them. my car at 800 rpm was reading appx 500mbar, if how you explained it is true, then that's probably normal and I thank you for educating me!!!
    if you're seeing 500mbar, that means you're on a bigger map sensor file (ie. 5120 hack).

  8. #8
    Active Member One Ring
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    Nov 15 2014
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    Hawaii

    The MAP sensor is before the throttle plate. I do not believe you will ever read vacuum from the stock sensors. You need a boost/vac gauge to the intake manifold.

  9. #9
    Veteran Member Three Rings
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    Quote Originally Posted by NOTORIOUS VR View Post
    if you're seeing 500mbar, that means you're on a bigger map sensor file (ie. 5120 hack).
    you are correct, I have a 3 bar map sensor installed. just curious. I like to know if what im looking at is normal
    2008 Ibis RS4....GETing tuned

  10. #10
    Veteran Member Four Rings NOTORIOUS VR's Avatar
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    Quote Originally Posted by axnjaksn View Post
    you are correct, I have a 3 bar map sensor installed. just curious. I like to know if what im looking at is normal
    Yep, then you're good to go.

    also rcoolb2002 is correct, the sensor will never read vac... it will only read ambient pressure + boost.

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