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Thread: Fuel Level Sending Unit Confusion

  1. #1
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    Fuel Level Sending Unit Confusion

    Greetings,

    I have just purchased a new to me 2003 R1150RT.

    I have found the fuel level indicator on the RID unit to be somewhat unreliable. On my first trip I noticed that it only dropped about two bars and then no change. But later on the ride I noticed that the indicator started working, and I watched the bars, now indicating lower, light up and go away as I went down a pretty good hill and back up the other side. After we stopped for a break it was back to the original two bars down. I have not run the tank down far enough to get a low fuel light as yet.

    I have both a Haynes and a Clymer book and in looking in them they show a float type indicator attached to the pump filter assembly. When I go to the online parts fisch, It shows an additional tube type sender that attaches from the top of the tank. This sender is not indicated in either of these two books.

    So, what do I have? And then what can I do to fix it? I am coming off of a K1100 and it is an entirely different animal.

    Thanks
    Rod

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    It is a resistor sender. Often the arm gets bent from changing the fuel filter. Also the connector for the tank electrical is not sealed, and may get intermittent. Some dielectric silicone may help it.

    Rod

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    Quote Originally Posted by rkildu View Post
    And then what can I do to fix it?
    Honestly, I would just reset the trip meter at fillup and watch for about 280 to show up. Or just wait for the low fuel light at which point you still have about a gallon (say 40 miles).

    I'm not sure but the 1150's sensor may not be exposed to the fuel. I know it is a different technology than what I have on the 1100.

    On the 1100 it is a simple rheostat and sits exposed to the fuel. I have had erratic readings a couple of different times, and I seem to have fixed it with a "shock treatment" of a full bottle of STP Fuel System Cleaner (in the silver bottle). The fuel gauge has worked perfectly for a few years now.

    It might be worth a try.

    The sensor and float are mounted on the fuel pump plate in the tank tunnel.
    The other thing may be a separate switch for the warning light.
    I have been in there to replace the fuel filter, and it wasn't really difficult.
    Just a PITA to dig down through all the tupperware.

  4. #4
    not so retired henzilla's Avatar
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    On the RT, it uses the float on the fuel pump to operate the low fuel warning as it does on all the models with that set up.

    The right front top of tank mounted tube is the float sensor for the fuel level display only used on the RT...I have seen those tubes pretty gummed up from stale fuel/moisture.
    Steve Henson
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  5. #5
    Pepperfool GSAddict's Avatar
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    Quote Originally Posted by henzilla View Post
    On the RT, it uses the float on the fuel pump to operate the low fuel warning as it does on all the models with that set up.

    The right front top of tank mounted tube is the float sensor for the fuel level display only used on the RT...I have seen those tubes pretty gummed up from stale fuel/moisture.

    Correct, The RT is different from other models.
    I have taken the tube apart and VERY GENTLY cleaned the resistance wire with a pinched piece of scotchbrite (sliding up and down)
    Clean the sliding contact on the float as well. RID will read correctly after that.
    Note: You have to remove the fuel pump plate and unplug the tube plug before the tube can be removed.
    Last edited by GSAddict; 11-04-2013 at 03:57 AM.
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    Recently read an interview with BMW m/c exec (do not recall his name, sorry) who stated that BMW bike fuel cell sensors are meant to only accurately measure the last half of the fuel in the cell. The sensors and gages are mostly useless until you get to about the half full (or half empty) level. That makes some sense when you consider the "interesting" shapes of the various fuel cells and how difficult it is to accurately measure the level of fuel therein. My personal observation is that the gage reading does seem meaningless until I get about 125-130 miles on a tank of fuel, then the gage begins to drop steadily with mileage until the low-fuel light comes on at somewhere around 175 miles.
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  7. #7
    Registered User arthurdent's Avatar
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    Quote Originally Posted by royce View Post
    Recently read an interview with BMW m/c exec (do not recall his name, sorry) who stated that BMW bike fuel cell sensors are meant to only accurately measure the last half of the fuel in the cell. The sensors and gages are mostly useless until you get to about the half full (or half empty) level. That makes some sense when you consider the "interesting" shapes of the various fuel cells and how difficult it is to accurately measure the level of fuel therein. My personal observation is that the gage reading does seem meaningless until I get about 125-130 miles on a tank of fuel, then the gage begins to drop steadily with mileage until the low-fuel light comes on at somewhere around 175 miles.
    This is a lot like my experiences with fuel indicator. Makes more sense than any of the other explanations I've seen in the past. (04 1150 GS)

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    Thanks for the information folks. Especially the comment about removing and cleaning the "fuel tube". I cannot find anything in my books about it at all.

    I cleaned the connector under the tank today with contact cleaner and put some dielectric grease on it. We will see. The bike apparently sat idle for a time based on what I am finding. Had a coil failure and just got that fixed, so my calculated gas mileage is probably off. I'm trying to get a feel for how many miles I can get per tank and about when the low fuel light will come on. I have an Airhead so I know about using the odometer to judge fuel, I just need a starting point.

    What would be an average MPG figure for this thing? That would also give me a starting point. My one trip I refueled 3 times and my mileage is all over the place due to the weak coil, I hope.

    Rod

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    Quote Originally Posted by rkildu View Post
    What would be an average MPG figure for this thing?

    Rod
    I'd say the average is 45 - you can force it down to 40 if you ride the absolute crap out of it.
    That's why I said when the light comes on you should plan to refuel within about 40 miles.
    If you buy unleaded premium and run 55 MPH, it will get 50 MPG.
    Top gear is pretty tall so you may not be able to stay in it, but at 55 it doesn't have a huge impact (the motor is more efficient revved a little higher).

    I also watch the elapsed miles to wave the Ducati over for fuel since his sender doesn't work either.

  10. #10
    MOA #24991 Pauls1150's Avatar
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    Mileage - I've gotten as low as 34 (downtown, or local high-rpm twisties) and as high as 52 (high-altitude slab droning).

    After the tube/etc is verified as OK, one more thing to keep in mind is the internal shape of the the gas tank itself: there is no crossover between the left and right sides, and they're both pretty deep, so when you lean right, you get more gas on the sender/pump side.

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    All right, I can live with a 45 mpg average, that is comparable to what my K1100LT got. that will give me pretty near to 250 miles before the fuel low light comes on.

    It's a good place to start anyway.

    I'm going to put some techron (sp?) in the tank to try to clean things up. It may help the RID indicators accuracy?

    Thanks
    Rod

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    Quote Originally Posted by rkildu View Post
    techron [...] It may help the RID indicators accuracy?
    Well, I think it might, since in your case the issue may be exposure to old gas and barn air.
    We can only hope though.

    Keep in mind that my 1998 R1100RT has a different material (wire, I think) in the sender than your newer model, which I believe is a semi-conductive plastic.

    I have not used techron in particular. I do not know if it is superior to the STP cleaner I used (may be similar).
    I would raise a small red flag here to avoid too many applications of the stuff too close together, as I have heard that if used to excess it can dissolve the built-up carbon and gum formations in the rings which contribute to the engine's "broken in" status.
    They would grow back but it may burn/blow oil for a time.

    Someone with direct Techron experience can weigh in.

    BMW says the 1100 holds 7.1 gallons, but Iron Butt says 7.5 - I'm pretty sure Iron Butt is more concerned with it than BMW was.
    I usually don't do any particular kind of riding - don't try to impress anyone but I don't go slow just to conserve fuel either.
    My light usually comes on right around 260. Usually the last bar has gone out just before that. And, typically I will get nervous and fill up around 280 and use about 6 gallons. (confirming yet again there was no need to be nervous).

  13. #13
    Day Dreaming ... happy wanderer's Avatar
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    I think if you want the RID working correctly and you know it's varnished up some your best advice was in post number 5. Clean the tube out.

    If you are only a gallon away from running out remember that possibly half of it is on the left side as mentioned before. You can't use that gas without tipping the bike over to the right side severely.

    I think it's a good thing to have your low fuel warning light coming on with a bar or two remaining on the RID since at this point the pump is still somewhat if not completely submerged which keeps it cooler. Changing out fuel filters can lead to some bending of the low fuel float arm causing it to be a bit off which is easily corrected. But be careful when bending. It does not take much.

    Cleaning the low fuel light warning sender unit is best done directly. I seriously doubt Techron or any other our in fuel system solvent is going to clean the printed circuit board contacts very well. When I change fuel filters on my RT I use a Q tip doused with isopropyl alcohol and gently clean the contacts. This leaves the few angstroms of gold intact and gets it squeaky clean which is what you want.
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  14. #14
    RD'nNH&AZ rdhudson's Avatar
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    So close!

    Odd you can judge a few angstroms. I have to resort to an RCH which I am more familiar with.
    BTW my R1100R has a metal tank and the left depression is blanked off so no gas occupies that side and no amount of leaning will give you the splash we used to rely on back in the day to get us to the filling station when we had forgotten to return the petcock to "on" from "reserve." Oh yeah I guess I will now have two terms to explain to the the younger non-engineers. Both seemingly related. (No its not my Pet.)
    2002 F650GS, 1998 R1100R 75th anniversary edition, 1983 R80RT (just sold), 1959 R60 (in restoration), Honda CT90
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    Quote Originally Posted by rdhudson View Post
    Odd you can judge a few angstroms. I have to resort to an RCH which I am more familiar with.
    BTW my R1100R has a metal tank and the left depression is blanked off so no gas occupies that side and no amount of leaning will give you the splash we used to rely on back in the day to get us to the filling station when we had forgotten to return the petcock to "on" from "reserve." Oh yeah I guess I will now have two terms to explain to the the younger non-engineers. Both seemingly related. (No its not my Pet.)
    oh is that what you're calling it now?...

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