Page 1 of 2 1 2 LastLast
Results 1 to 15 of 19

Thread: Erratic fuel gauge

  1. #1
    Join Date
    Apr 2010
    Location
    Longford/Roscommon
    Posts
    886

    Default Erratic fuel gauge

    Have been searching for info on this but can't find a suitable reference. Problem is that the gauge shows at full most of the time and only briefly shows the correct fuel level. Luckily, the low level warning light is working. I did clean the nut some time ago in the cluster and the gauge worked ok for a while after that. There is only one sender unit in this as its a 316i so maybe this is kaput. I checked that there is power coming to the sender unit. All other gauges are working. Not a major issue but would like to get it sorted. I either need a gauge or a sender unit but which?

  2. #2
    Join Date
    Jan 2009
    Location
    mallow.co.cork
    Posts
    2,241

    Default

    i'd say its the nut again to be honest, make sure to clean all the connections with a bit of sandpaper
    https://www.facebook.com/AlienWorkshops

    M40 RIGHTNESS.
    if you can get to 6500rpm, nobody can hear your tappets.

    Quote Originally Posted by Torq View Post
    When Age says he wants it cheap, he means Cheaaaaaaaaaaaaaaaap!
    Torq

  3. #3
    Join Date
    Apr 2010
    Location
    Longford/Roscommon
    Posts
    886

    Default

    Will do, thanks age. Bit of a pain taking out the cluster---was hoping it might be the sender unit but not sure how one would test this.

  4. #4
    Join Date
    Sep 2007
    Location
    dublin
    Posts
    1,539

    Default

    if you are prepared to take the sender unit out of the fuel tank
    and have a multimeter it can be checked.
    _______________________________


  5. #5
    Join Date
    Apr 2010
    Location
    Longford/Roscommon
    Posts
    886

    Default

    I have taken the sender unit out and cleaned the connections on it xworks. I also do have a multimeter. Can one open this dip tube type unit as I think the float is inside it and could be sticking maybe? The gauge flickers to full though as if its a broken connection.

  6. #6
    Join Date
    Sep 2007
    Location
    dublin
    Posts
    1,539

    Default

    Before removing the sender you can do a resistance check to see if it's the
    the source of your trouble.

    Depending upon the type of sender you have, the 3 terminals may or
    may not be marked. The marking are (g), (w) & (31). You are only
    interested in two of them (g) and (31).
    (terminal (w) is for the low fuel warning light).

    If your fuel level sender hasn't got the terminals marked then pull back
    the rubber boot on the sender connector to reveal the 3 wires conecting
    to the sender.
    There should be a brown/green, a brown/grey and a brown wire.
    You are looking to identify the 2 terminals the brown/green and the
    brown wire connect to.

    Once you have identified the two terminals on the sender unit, set your
    multimeter to do a resistance check (200 ohm position) and connect
    the two multimeter probes to the two sender terminals.

    A full fuel tank will read very close to 0 ohms (maybe 2 or 3 ohms).
    An empty fuel tank will read close to 60 ohms.
    And depending on how full the tank is the reading should fall somewhere
    between 0 & 60 ohms.

    If you get a reading anywhere between 0 and 60 and your fuel gauge is
    still reading full then it's unlikely the sender unit is the problem (unless
    your fuel tank actually is full to the brim).
    _______________________________


  7. #7
    Join Date
    Apr 2010
    Location
    Longford/Roscommon
    Posts
    886

    Default

    Thanks for the clear write up on that. Would like to at least eliminate the sender unit as its an expensive enough part to buy if not necessary.

  8. #8
    Join Date
    Nov 2009
    Location
    Offalyman in Laois
    Posts
    8,887

    Default

    This should be 'stickied'
    1990 E30 316i M42B18 Matte Black 2 Door
    1995 E34 518i Techno Violet Metallic Saloon

  9. #9
    Join Date
    Feb 2009
    Location
    N69, Co.Limerick
    Posts
    3,928

    Default

    Quote Originally Posted by LaoisE30 View Post
    This should be 'stickied'
    yep
    I'm currently buying some old parts
    Click here.
    Upgrades offered:
    One touch Windows
    OBC Light Bars
    Remote central locking for E30s

  10. #10
    happy's Avatar
    happy is offline Premium Member (Site Supporter)
    Join Date
    May 2006
    Location
    east cork
    Posts
    1,562

    Cool

    I don't know about the single sender ones but I've had trouble with the fuel gauge being erratic on two of my e30's turned out to be the wiring going into the sender on the left hand side of the tank extended the wires a little and haven't had a bother since!
    [00=[||]=00]

  11. #11
    Join Date
    Apr 2010
    Location
    Longford/Roscommon
    Posts
    886

    Default

    Wouldn't have thought so here happy as the wires and connections look good. When I pull the connecter off the sender unit, the gauge then shows empty As a follow up to xworks instructions, it looks like the sender unit is ok. Resistance is reading at 55.6 with the tank empty and 04 with the tank full with the multimeter terminals connected to the brown/green and brown connections on the sender unit assuming I am reading this right. It does look like attention now moves to the gauge.
    Attached Images Attached Images

  12. #12
    Join Date
    Sep 2007
    Location
    dublin
    Posts
    1,539

    Default

    It is starting to look like the fault may be in the gauge itself or in the dash
    cluster. But to narrow it down a little further there is another test you can
    do with the multimeter.

    This test is to check the wire leaving the dash cluster and traveling all the
    way down to the fuel tank sender unit is ok (brown/green).

    Before you start you'll need to know the resistance again at the two terminals
    of the fuel tank sender you've just checked. If the tank is still full
    it can be better to use up a bit of fuel to drop the level back to half full or
    anywhere other than full.

    As you've seen from your checks the sender reads about 4 ohms with a
    full tank of juice and 56ish ohms with the tank near empty. For the next
    test ideally you want the sender to be reading 15 ohms or more (so
    anywhere from three quarters full to nearly empty.)

    The reason for this is if the brown/green wire had been rubbing against the bodywork
    somewhere along it's run and was now touching bare metal, then when you go to test
    the resistance along this wire you will measure 0 ohms. As a full tank of fuel also reads
    close to 0 ohms then you can never be sure if the wire is reaching the fuel tank sender ok
    or shorting to earth along the way.
    At least if the fuel level has dropped down a bit the sender should be reading 15 ohms or more,
    and then if you check the brown/green wire and find 0 ohms you can now be sure theres a problem
    with the wire.

    Once you've got your ohm measurment at the tank sender pins
    (for arguments sake we'll say 30ohms),reattach the connector plug to the
    fuel tank sender and make sure it's nice and secure.
    Your now going to check the other end of the brown/green wire up at the dash
    where you should find the exact same reading (30ohms).

    To find the brown/green wire up at the dash you'll need to get access to
    the rear of the dash cluster. Once you've done this you'll see 2 connector
    plugs plugging into the rear of the dash cluster, a white and a blue plug
    (there may also be a yellow and green plug if your car has an on board computer
    or cruise control).

    The plug you are interested in is the white plug (C2) as it contains the
    brown/green wire leaving the cluster and heading for the fuel tank sender.
    You are looking to identify terminal number 4 of this plug.
    The picture below should help identify it. Looking head on at the
    connector it's 4 up from the bottom on the left hand side...........



    Unfortunately the holes in the connector are too small for the probe of
    your multimeter to fit in to, so, you'll need a small strand of wire or a paper
    clip to push into this hole to make contact with the pin inside. (gently)

    When you have the wire/clip in place, set your multimeter to the
    200ohm setting again, touch one probe off the piece of wire sticking out of
    pin 4 and touch the other probe off the battery earth terminal or a decent
    earth point on the car (ignition barrel is usually a decent earth).

    You should get exactly the same ohm reading as you got when testing
    the two pin's back at the fuel tank sender (+ or - 1ohm).

    If you do, the wire from the dash cluster to the tank sender unit is sound
    and the next step would be to swap in a different fuel gauge to the cluster.

    (If your working at the back of the dash cluster while lying the cluster forward
    on top of the steering coloum shrouds, it can help to place a rag/cloth over the
    shrouds first to stop the clear perspex at the front of the dash cluster picking up
    irratating scratches)
    Last edited by xworks; 26-10-2012 at 02:35 PM.
    _______________________________


  13. #13
    Join Date
    Apr 2010
    Location
    Longford/Roscommon
    Posts
    886

    Default

    Thanks for easy to follow instructions and online tutorial as well as saving me the price of a sender unit. Resistance at the sender unit and gauge connecter are similar as you suggested. Had driven about 100 miles yesterday and seem to have used up about 4 Ohms worth of petrol. The fuel gauge has been working since it was filled but I also cleaned/tightened the nut on the back of the cluster when I had it out. Many thanks for your help and I can probably set up now as a sort of certified tech.
    Attached Images Attached Images

  14. #14
    Join Date
    Dec 2009
    Location
    Bristol and Cork
    Posts
    55

    Default

    Can this be Sticky'ed? It is an excellent write-up
    Colm Deasy
    '93 BMW E30 Touring 1.6i

  15. #15
    Join Date
    Jul 2013
    Posts
    141

    Default

    Mine gives me 74.8 and the tank is somewhere at 1/4. Is this correct?

Thread Information

Users Browsing this Thread

There are currently 2 users browsing this thread. (0 members and 2 guests)

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •