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Thread: Fuel Gauge inaccurate, but fun!

  1. #1
    Join Date
    Aug 2005
    Location
    North East Florida
    Posts
    54

    Default Fuel Gauge inaccurate, but fun!

    I noticed that I was approaching empty the other day and didn't remember using all that much fuel. When I went to fill up, the pump stopped at 7 gallons. Thinking it was due to back pressure, I pulled the handle out slightly and filled some more. About 1/4 gal and it would not take any more fuel. Stubbornly thinking, I tried again and ended up overflowing. Hmmm.

    After pulling out of the gas station I noticed that I only had a half tank. Thinking to myself... Why would the tank only fill half way up? Was there a balloon in the tank taking up space? Was there a fuel pressure issue which was making the fuel bubble out of the tank? Probably not. After a few miles I noticed that I only had a 1/4 tank. Wow! What a guzzler!!! I stopped to check for leaks. Didn't see or smell any fuel. So I started up and behold, I had a half tank again! Like a visit from the gas fairy. This went on all day, each time I stopped, shut the car off and started up again, the tank would fill back up to 1/2 then rapidly drop down to empty. I thought to myself again, if this were only real! I could simply stop and wish for more fuel and wahoo! More fuel!

    Then reality kicked in. I have a faulty fuel gauge system. So the question is, What's going bad, the sending unit in the tank or the gauge in the dash? I've seen where the capacitors go bad, but before I go ripping the dash out, I'd like to make sure that is the culprit.

    Has anyone had a similar problem with the fuel gauge?
    If so, what was the fix?

    Thanks!

  2. #2
    Join Date
    Dec 2003
    Location
    Eastern Tennessee USi
    Posts
    14,843

    Default

    sure the tank hasnt caved in from vacumme? Not that uncommon a thing.

    Just my 2Ē which is now worth 1/2 cent with the devaluation of the US dollar.
    95 E34 530I V2.37
    ===========
    Those who make peaceful revolution impossible will make violent revolution inevitable.

    John F. Kennedy

  3. #3
    Join Date
    Mar 2005
    Location
    Barrie Ontario, Canada
    Posts
    437

    Default

    my gas gauge is very odd aswell, likes to sit at the 1/4 mark

    and bounces around like a nutter everyonce and a while.




    J.McWatters

  4. #4
    Join Date
    Oct 2004
    Posts
    3,395

    Default

    check the sending unit first.

    We picked up a 750iL for a grand on ebay. Guy claimed it wouldn't start due to an electrical fire. We checked the harness and one non critical item was burned.

    Albeit the fuel gauge read half a tank, removing the pump indicated that, in fact, the car was just out of gas.

    Car now has gas and runs as one of our loaners.

    best, whit

  5. #5
    Join Date
    Jun 2004
    Location
    Melbourne, Australia
    Posts
    1,305

    Default

    Quote Originally Posted by Been-Jammin
    I noticed that I was approaching empty the other day and didn't remember using all that much fuel. When I went to fill up, the pump stopped at 7 gallons. Thinking it was due to back pressure, I pulled the handle out slightly and filled some more. About 1/4 gal and it would not take any more fuel. Stubbornly thinking, I tried again and ended up overflowing. Hmmm.

    After pulling out of the gas station I noticed that I only had a half tank. Thinking to myself... Why would the tank only fill half way up? Was there a balloon in the tank taking up space? Was there a fuel pressure issue which was making the fuel bubble out of the tank? Probably not. After a few miles I noticed that I only had a 1/4 tank. Wow! What a guzzler!!! I stopped to check for leaks. Didn't see or smell any fuel. So I started up and behold, I had a half tank again! Like a visit from the gas fairy. This went on all day, each time I stopped, shut the car off and started up again, the tank would fill back up to 1/2 then rapidly drop down to empty. I thought to myself again, if this were only real! I could simply stop and wish for more fuel and wahoo! More fuel!

    Then reality kicked in. I have a faulty fuel gauge system. So the question is, What's going bad, the sending unit in the tank or the gauge in the dash? I've seen where the capacitors go bad, but before I go ripping the dash out, I'd like to make sure that is the culprit.

    Has anyone had a similar problem with the fuel gauge?
    If so, what was the fix?

    Thanks!
    When you think of E34 idiosynchrosies include inaccurate fuel gauge.
    Once mine gets below about one half to a third full you may as well forget it.
    By the time it gets to a quarter it can suddenly drop to zero, then the low fuel light comes on. Next time I look at it it's back up to quarter again.
    I tried cleaning the wire resistor and wiper on the sender unit but it made no difference. It appears the bottom part of the plastic housing tube that contains the sender mechanism tends to crack around the nut on the end of the rod that supports and centralises the float causing the float to foul against the housing tube. The float doesn't begin to foul until the tank gets to below about half full. I can't really see an easy way to reliably repair this as you would need some kind of glue that was not effect by the fuel.

    1990 E34 535iA, 215,000kms (130,000 miles).
    Dual Climate, Rear Headrests, Rollerblind, M-Tech Wheel,
    Memory Seats, EAT Chip, T-Stars.

  6. #6
    Join Date
    Dec 2003
    Posts
    571

    Default

    WOW! I thought mine was unique! It's pretty accurate between 20-80L, but between R-20 it's all over the place. It can be sitting on empty for a week, then you fill it up and it only takes 65L or so. I find that the Range is more accurate than the fuel guage.

  7. #7
    Join Date
    Mar 2005
    Location
    Long Beach, CA
    Posts
    2,563

    Default

    Quote Originally Posted by pundit
    When you think of E34 idiosynchrosies include inaccurate fuel gauge.
    Once mine gets below about one half to a third full you may as well forget it.
    By the time it gets to a quarter it can suddenly drop to zero, then the low fuel light comes on. Next time I look at it it's back up to quarter again.
    I tried cleaning the wire resistor and wiper on the sender unit but it made no difference. It appears the bottom part of the plastic housing tube that contains the sender mechanism tends to crack around the nut on the end of the rod that supports and centralises the float causing the float to foul against the housing tube. The float doesn't begin to foul until the tank gets to below about half full. I can't really see an easy way to reliably repair this as you would need some kind of glue that was not effect by the fuel.
    Mine is fine till it gets to 1/4 tank, then is likes to bounce around to empty and back. I've found that the range on the OBC is pretty accurate though as a backup,

    Ralph Mendoza Jr. - Long Beach, CA

  8. #8
    Join Date
    Mar 2005
    Location
    Long Beach, CA
    Posts
    2,563

    Default

    Quote Originally Posted by uscharalph
    Mine is fine till it gets to 1/4 tank, then is likes to bounce around to empty and back. I've found that the range on the OBC is pretty accurate though as a backup,
    I used to just bang on the dash and the needle would return to where it should be, but I stopped doing that. I don't thinks it's good for the instrument cluster. The other night the digital odometer went out, until I banged on it again. I'll just rely on the range on the OBC for now.

    Ralph Mendoza Jr. - Long Beach, CA

  9. #9
    Join Date
    Feb 2005
    Location
    Grand Marias USA
    Posts
    155

    Default

    Mine is just lazy, when I start her up the guage barely moves, but within about 2 min it shows the proper level.

  10. #10
    Join Date
    Aug 2005
    Location
    North East Florida
    Posts
    54

    Default

    Quote Originally Posted by 632 Regal
    sure the tank hasnt caved in from vacumme? Not that uncommon a thing.

    Just my 2Ē which is now worth 1/2 cent with the devaluation of the US dollar.

    I've never heard of such a thing, but I will certainly have a look when I check out replacing the sending unit.

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