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Thread: How does fuel sensor work in VW-s?

  1. #11
    Verified VCDS User golfi_vend's Avatar
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    Quote Originally Posted by Spacewalker View Post
    But what is your problem friend ?
    Nothing, just trying to figure out some stuff.



    Hi DV52. The second sensor is just for 4motion(4WD) models. If we're dealing with 2WD then second sensor is blank. Same reason for dividing sum with 2.
    If i config my CAN coding for 2WD then second sensor isn't used. I can make a pic.

    About temperature, I'm not sure if this makes so much difference. Note, the first pictures are taken day before the last picture. See the mileage.
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  2. #12
    Verified VCDS User golfi_vend's Avatar
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    Today, fuel light came on said 40km left, drove about 20km and it said 30km left. Picture before filling up.

    Second pic after filling, driving about 50km


    And this is when i code my can to 2wd.
    I am a VW Freak - Le WV Freaks OR Come visit me at my work with ODIS concerns - FORSS ODIS GeKo/FaZit access for VW/AUDI/Škoda
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  4. #13
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    Golfi_vend: Your new data (via the pics^^^) just provide further confirmation that the measuring block value for "Fuel Sender Resistance" matches the calculated value (to a whole number). I've rearranged the table below so that it is ordered by litres in the tank



    The one interesting observation is that the measuring block value for "Fuel Gauge 2 Resistance" dropped to 88 ohms when you filled the tank after staying constant around 287 ohms - even when the tank was empty! Why is that?
    Also when you change to a single sensor (2WD), you lose 5 litres in the tank!
    Incidentally, how do you switch between one and two sensors in the measuring block?
    Last edited by DV52; 02-06-2015 at 12:31 AM.
    VW Golf MkVII (MY13) - A3 8V hatch (MY17)

  5. #14
    Verified VCDS User golfi_vend's Avatar
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    I guess you find the answer to your question about second fue lsender from following pictures.

    2WD
    http://i148.photobucket.com/albums/s...k/fwdtank1.jpg
    4WD(like mine)
    http://i148.photobucket.com/albums/s.../r32tank01.jpg
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  7. #15
    Verified VCDS User NZDubNurd's Avatar
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    Quote Originally Posted by DV52 View Post
    The one interesting observation is that the measuring block value for "Fuel Gauge 2 Resistance" dropped to 88 ohms when you filled the tank after staying constant around 287 ohms - even when the tank was empty! Why is that?
    There is a venturi type arrangement that pulls the fuel from the left side across to the right. So the left side gets scavenged into the right, eventually all the fuel ends up in the right side, as the tank gets empty.

    I've got to fit ther 4wd A3 tank into the Touran, so I have a 4-motion tank in my garage right now

  8. #16
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    Quote Originally Posted by NZDubNurd View Post
    There is a venturi type arrangement that pulls the fuel from the left side across to the right. So the left side gets scavenged into the right, eventually all the fuel ends up in the right side, as the tank gets empty.

    I've got to fit ther 4wd A3 tank into the Touran, so I have a 4-motion tank in my garage right now
    NZDudNurd: OK, so are you saying that when Golfi_vend had 20-ish litres in his tank (and less), the scavenging mechanism fixed the "Fuel Gauge 2 Resistance" to about 287 ohms and when the tank was filled, the No2 sensor returned to its native resistance of 68 ohms because there was no need to scavenge fuel across the tank sides? Das brilliant - what a clever lot those German engineers are!!
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  9. #17
    Verified VCDS User NZDubNurd's Avatar
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    Quote Originally Posted by DV52 View Post
    NZDudNurd: OK, so are you saying that when Golfi_vend had 20-ish litres in his tank (and less), the scavenging mechanism fixed the "Fuel Gauge 2 Resistance" to about 287 ohms and when the tank was filled, the No2 sensor returned to its native resistance of 68 ohms because there was no need to scavenge fuel across the tank sides? Das brilliant - what a clever lot those German engineers are!!
    My understanding is that the scavenging is done by the return line from the fuel pressure regulator, but it sucks fuel from the left side, and pumps it into the right side. When the right side is full, it over flows back into the left side (over the saddle between thew two halves). As the fuel level decreases, there isn't enough fuel to overflow back into the left side, so it all ends up in the right side. The left side should always show empty first (287-ish ohms).

    Example, at say 40L, gauge 1 may read 60 Ohms (full) but gauge 2 may read 140 Ohms - in effect, the fuel is used from the gauge 2 side of the tank first.

    Changing to read both guages (senders) is done by coding as 4-motion/4wd.

    I tried it in the Touran... makes the guage very inaccurate

  10. #18
    Verified VCDS User golfi_vend's Avatar
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    I think i figured it out. I really hope.

    I'll talk T32 connector terminology, so it'll be easier to follow.

    What i think is that at first, resistance is measured between pin1(3) and sensor ground. Then it's measured between pin2(4) and sensor ground. 2 resistances are get.
    Then resistance between pin 1(3) and 2(4) is measured and total resistance is get. Then the first two are summed together and total resistance is subtracted. A pad resistance is got.


    http://s16.postimg.org/5025qzisl/Image_6.jpg

    What you think? Is it plausible?
    I am a VW Freak - Le WV Freaks OR Come visit me at my work with ODIS concerns - FORSS ODIS GeKo/FaZit access for VW/AUDI/Škoda
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