Why 1150GS gas gauges dont work.

Discussion in 'GS Boxers' started by kelsokid, May 26, 2009.

  1. kelsokid

    kelsokid Where to next

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    My fuel gauge was starting to develope the dreaded wont show full syndrome, and after trying to live with the darn thing I finally decided to dig into the problem. Turns out the Bavarian magicians who designed this bike were not familiar with the whole periodic table, and missed the joys of Au. They speced in a power connector for the fuel tank connection, which would have been fine if the only thing it had to do was get power to the fuel pump. But they completly missed that the cheap tin plated power connector pins corrode with time and are known in some parts of the engineering world for their unsuitability in precison applications. The damn thing builds up a small amount of resistance in both the gauge line and in the ground return line, which the display interperts as lower fuel levels. Turns out that the gauge expects about 3.5 ohms circuit resistance to dispaly full, but mine was about 7.2 ohms when the tank was filled. I made a little pin jumper for both the gauge line and the ground line, and voila... the gauge jumped up to displaying FULL.
    Solution is a new electrical connector blessed with non-corrodable gold connection pins.
    Parts from Digikey
    1ea. A1351-ND
    1 ea. A1300-ND
    2ea. A1342-ND
    2ea. A1343-ND
    2ea A25131-ND
    2 ea. A25012-ND

    Parts will add up to about $35 or so, but the gauge should work for as long as you own the bike.

    Cheers
    #1
  2. Jarvis

    Jarvis DC GSer Administrator Super Moderator

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    Thanks.
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  3. PETDOC

    PETDOC Long timer

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    Can you post a picture of your pin jumper?
    #3
  4. Steptoe

    Steptoe steptoe

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    Thats why they make dielectrical grease -

    Has your bike been serviced professionally ?

    It should be used on all electrical plugs/connections on a motorcycle.
    #4
  5. jpalamar

    jpalamar Long timer

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    Too bad the solution for the gas gauge not applicable to the hexhead models! :D
    #5
  6. lm002e

    lm002e Been here awhile

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    Thanks a lot for this post. This is the exact problem I'm having with my '04 GSA fuel gauge. If there's any way you could post up pics of the problem and solution, I'd be very appreciative. Thanks again!
    #6
  7. loeky

    loeky Been here awhile

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    Would love some visuals on this as well. It appears to be the only thing wrong and would like it to work. :2cry
    #7
  8. Poolside

    Poolside Syndicated

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    <BR>
    The 'won't show full syndrome', and it's partner 'won't show empty syndrome', are caused by hysteresis in the gauge display electronics. Not only does the gauge display processor have hysteresis, it also has filtering to keep the displayed level steady despite fuel sloshing in the tank.

    <BR>
    #8
  9. GS Addict

    GS Addict Pepperfool Supporter

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    Not to mention 'sludge' on the sender. Part of the fuel filter replacement is cleaning the traces on the sender board when I do mine or anyone else's. Been lot's of problems up here in BC from deposits coming from pipeline gas.
    #9
  10. Poolside

    Poolside Syndicated

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    <BR>I've never seen that to be the case.

    There are, however, 2 fuel level signal wires from the 1100/1150 tank. One is the 'fuel level' signal, and the other is the 'low fuel' signal. They operate independently. The 'fuel level signal wire' is used by the fuel level bar-graph gauge, and the 'low fuel signal wire' is used for the low fuel light.

    The low fuel light always operates at the same level of fuel, it functions similar to a mechanical switch.

    The fuel level bar-graph gauge processor has hysteresis, and because of that the bar-graph often reads differently from fill-up to fill-up. The variation in the bar graph display, unknown to the rider, makes it appear as though the low fuel light comes on at different fuel levels. But what's actually going on is the bar-graph gauge will display 'full' at differing fuel levels, and will also display 'empty' at differing fuel levels. The fuel levels which the processor considers as 'full' or 'empty' is always in flux. That's because the processor bases what it considers as 'full' or 'empty' on the most recent persistent quantity of fuel in the tank. It's poor software in the processor that causes that.

    What the rider sees is sometimes the low fuel level light illuminates while the bar-graph gauge reads 'half tank', and sometimes the low fuel light doesn't illuminate until the gauge has read 'empty' for a time. The low fuel light is trustworthy, but the bar graph gauge is for entertainment purposes only.

    <BR>
    #10
  11. Schlug

    Schlug JockeyfullofBourbon

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    put something on and stay in that position.
    wow, Poolside, that was an excellent post.

    i've only had my GS for 9 weeks or so, put on 5.5k, and only once has the low fuel light come on. i was convinced that it didn't work, and i remember reading in the manual that it should light at 2 bars. well, i was at one bar, no light, and close to home. i decided to push it, and when i finally had zero bars, i fueled it up, resigned to the fact that my low fuel light didn't work.

    and this isn't good news, because sometimes i get wrapped up in riding and forget to check the fuel level, or end up hooning it home and burning up quite a bit more than i would have expected.

    about a week ago i was about 3/4s the way home and the fuel light came on. no i understand how things work.

    i believe i filled it with just a tic over 5 gallons, which means it trips when i have .5 gallons in reserve? that seems low, man. that could be 15 miles depending, 20 miles more like it.
    #11
  12. Poolside

    Poolside Syndicated

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    <BR>Thanks Bobby. I know what you mean about not knowing how far you can make it. There is some published data on the usable fuel in the tank for the 1100 and 1150. The exact fuel level that the low fuel light comes on will differ a little bike-to-bike, but it will be consistent on any particular bike. I usually run my tank down to very near empty, and have put in as much as 6.2 gallons in a standard GS 1150 tank. I use fuel pump whine as the low fuel indicator. By that time the low fuel light has been on a while.

    The fuel pump whine isn't hurting anything, motor noise is audible when a portion of the motor becomes 'unsubmerged' due to fuel sloshing. The fuel pump motor isn't cooled by fuel. It could be mounted externally if it were plumbed for it. The pump uses about 15 watts of power and is roughly 70% efficient. It dissipates roughly 4.5 watts as heat, making the motor body no more than slightly warm to the touch.
    <BR>
    #12
  13. Mr Head

    Mr Head Adventure Hippie Supporter

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    My bike after riding it for around 130,000 miles and running it completely out of gas once.:D
    I know how my bike acts in regard to the idiot-bar-graph fuel level thingie, (I refuse to call it a gage)...

    It almost never shows full. Once in a great while it does show full, but not right after filling, sometimes miles down the road, say 100 or so.

    The low fuel light used to always come on at 268 miles showing on the odometer, (also in error, but I'll ignore that for now, the number was the same almost all the time), there were also two bars showing at the bottom.

    A couple of years ago so that would be around 90,000 miles or so, the bar graph shows no bars and the odometer shows between 245 and 298 miles, which probably really depends more on the sorry state of tune, and number of wheelies. The odd part is that the bar graph now goes all the way to no bars showing.

    Now, what is fun about this is that the level in the tank has not changed as far as I can tell based on how much fuel I can wiggle/force into the tank once the little yellow light glows. The amount used remains the same as close as I can tell for the entire 130,000 miles I've fiddled and wrung this thing.

    I "Fixed" my bar-graph gage issue by simply mounting my GPS in front of it.

    The display of bars, or no bars no longer bothers me.:wink:
    #13
  14. kelsokid

    kelsokid Where to next

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    "The 'won't show full syndrome', and it's partner 'won't show empty syndrome', are caused by hysteresis in the gauge display electronics. Not only does the gauge display processor have hysteresis, it also has filtering to keep the displayed level steady despite fuel sloshing in the tank."



    While I agree that the system has some hysteresis, that is not the problem. I am lucky(unlucky) enough to own two GS tanks, one of which I disassembled to do my analysis of this problem. After all was said and done, I was able to consistently get my gauge to show full if the sensor resistance was about 3.5 ohms ( I used an external precision resistor for this test), and it would show one bar down at about 7 ohms. I did this test repeatedly, and it works this way every time. Then I measured the sender, right at the connections to the external tank feed thru connection. My sender was 3.3 ohms when the tank fuel sensing float lever was all the way up, and it progresses to about 68 ohms when the lever is in the empty position. Then I measured resistance after the tank connector, and mine was running about 6.5 ohms with the tank full. So the tank connector was adding several ohms to the circuit resistance, which the display misunderstands to be a lower fuel level. Then I made a little jumper around he tank connector, so that the circuit resistance of the tank connector was eliminated, and the gauge immediatly and reliably showed all the bars (full) . I then installed the gold pin connector and the problem resolved.

    The stock connector slowly oxidizes with time, adding to the circuit resistance, and eventually it adds enough resistance to always show a bar or two low. A quick and easy short term solution is to simply make and break the tank connector a few times, this will wipe the connection surfaces clean, and drop the circuit resistance of the connector for a while. It is a simple way to test this solution, the gold connector is the way to eliminate the problem for all time.
    #14
    Chad likes this.
  15. kelsokid

    kelsokid Where to next

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    1. Heavy Brown ( 2 on tank side. 1 on the bike side, 16 awg?) is ground (earth to our funny talking island bound bretherin)

    2. Medium Green(18awg?), power to the fuel pump

    3. Small Yellow (20awg?) Fuel gauge sender

    4. Small White(20awg?) Low fuel light


    I'll try to post some pics in a couple of weeks. I will be out on the beast for a bit.
    #15
  16. ECMO4

    ECMO4 That's gonna' hurt!!

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    Poolside,

    Nice description, which may explain my gauge. It usually shows full until I get down to about half and then starts to drop. Not an issue since it's pretty consistent, just a bit strange. Anyway...

    I don't completely fill my tank, especially in the summer, unless I plan on going for a long ride. Usually run it down to the light and then put in 3-4gal and keep going. So, if I get your concept correctly, the processor has over time come to associate my half-tank fills as the normal full level and displays accordingly. Then when I do give a full bag it is still working off the old data. Is this correct?
    #16
  17. kelsokid

    kelsokid Where to next

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    I dont think that the display is that smart. It is just a display of the resistance from the tank sender, with some integration thrown in to smooth it out. The way poolside has it it would be a very unreliable system if you filled to different levels all the time. And I see no reason they would add that level of complexity to a simple system.
    I bet it just displays the sender loop resistance, nothing more.

    Please note that this applies only to the 1150GS, I have no information on the system design of the 1200's. My buddy who has one has so far not let me "explore" his bike's system.
    #17
  18. kelsokid

    kelsokid Where to next

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    Yup, has its own little wiper on the sender system, and closes a circuit near the bottom of the float travel. It should always come on at about the same fuel level, there is no reason that the loop resistance would play into its behaviour.
    #18
  19. tagesk

    tagesk Tuscan rider

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    I have taken the liberty of adding this thread to the GSpot FAQ (question 3.34).

    [TaSk]
    #19
  20. Poolside

    Poolside Syndicated

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    <BR>
    You're funny, Kelso :D

    <BR>
    #20