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post #1 of 19 (permalink) Old Jun 11th, 2011, 3:51 pm Thread Starter
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Fake out the fuel gauge?

After only 20,000 miles, it looks like my fuel level sender unit is kaput again. No chance of getting it fixed under warranty this time. I wouldn’t mind so much since I use the tripometer instead, except now I have a yellow caution triangle and flashing Fuel icon all the time.

So this weekend I pulled the plug for the fuel sender intending to short out the leads with an appropriate level resistance to fool the instruments into believing the tank is always full. There are four wires going into the sending unit: green/blue, green/red, brown/blue, brown/green. The brown ones seem to be ground. The green ones show no DC voltage when the ignition is on. What’s going on here? Is the oscillator for the capacitive sensor separate from the fuel sender unit, thus it's AC rather than DC to the sender unit? If so, is it possible to put a capacitor across the right leads to mimic a full tank? Why the ground leads?

Anyone have any ideas on how to proceed?
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post #2 of 19 (permalink) Old Jun 11th, 2011, 7:24 pm
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I'm not 100% on this but I htink some of those connectors are for the fuel pump
http://realoem.com/bmw/showparts.do?...00&hg=16&fg=14

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post #3 of 19 (permalink) Old Jun 11th, 2011, 8:17 pm Thread Starter
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Quote:
Originally Posted by GillyWI
I'm not 100% on this but I htink some of those connectors are for the fuel pump
http://realoem.com/bmw/showparts.do?...00&hg=16&fg=14
I don't think so. The bike starts and runs with it unplugged. There's another three-lead plug going into the same component, which I thought at first was for the sending unit, but when it's unplugged, I don't hear the fuel pump whirl when I turn the ignition, and the bike won't fire up.
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post #4 of 19 (permalink) Old Jun 11th, 2011, 11:32 pm
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Maybe this will help you, maybe not. 2008 R1200R Fuel Strip - BMW MOA The apparent design is some sort of Wheatstone Bridge for the strip. No doubt, our wunnerful ethanol may be playing havoc with the strip too.

I dunno, but one guy there has been through fuel strips like mad - like 6 times in one year! and yet another poster claims about 2,000 miles per strip.

You may be onto something if you can bypass the beast. I'm glad their 'cheaper' S1000RR has a float in it. Okay, the 'less cheaper' K1600GT/L also has the float back too.

I'm wondering if you can remove the strip and try cleaning it off? I know on my RT I had some purple sludge at the bottom of the tank and I don't know where it came from as all I used was Chevron gas in it. It was thick enough I used a putty knife to dish it out like jelly. Another tank I put some winter stabilizer in it and when I opened the tank cap, it had this white pepper-like stuff all over it that I could wipe off with my finger. Some stabilizer.

Good luck and let us know how the bypass works out.


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post #5 of 19 (permalink) Old Jun 12th, 2011, 5:34 am
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Quote:
Originally Posted by emzed
After only 20,000 miles, it looks like my fuel level sender unit is kaput again. No chance of getting it fixed under warranty this time. I wouldn’t mind so much since I use the tripometer instead, except now I have a yellow caution triangle and flashing Fuel icon all the time.

So this weekend I pulled the plug for the fuel sender intending to short out the leads with an appropriate level resistance to fool the instruments into believing the tank is always full. There are four wires going into the sending unit: green/blue, green/red, brown/blue, brown/green. The brown ones seem to be ground. The green ones show no DC voltage when the ignition is on. What’s going on here? Is the oscillator for the capacitive sensor separate from the fuel sender unit, thus it's AC rather than DC to the sender unit? If so, is it possible to put a capacitor across the right leads to mimic a full tank? Why the ground leads?

Anyone have any ideas on how to proceed?
First you need to find out EXACTLY what technology they are using to do the level sensing.

There are many but the most common are 1.) Simple float level connected to a variable resistor whose voltage varies with position. 2. High frequency where a common wire emits the signal and several or more pads or wires at different height pickup the signal if there is liquid in between. 3.) Thermistor type where a sensitive resistor is heated (By a very small amount!). When liquid is in contact, that part of the resistor is much cooler than the part in air. In all cases there is a voltage produced either variable or in a series of steps which the fuel level meter uses.

I had read that the strip may be a rubber composition. It could be conductive and that's how they make the vertical 'array' of resistors. If so it is no use just shorting out the wires as the system expects to see some resistance and not a short circuit.

Of course the simplest fuel gauge is to fit a clear plastic pipe in the bottom of the tank and have it run up the side, then calibrate the levels with a kitchen jug. That's how my electric kettle does it!



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post #6 of 19 (permalink) Old Jun 12th, 2011, 9:12 am
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Quote:
Originally Posted by emzed
After only 20,000 miles, it looks like my fuel level sender unit is kaput again. No chance of getting it fixed under warranty this time. I wouldn’t mind so much since I use the tripometer instead, except now I have a yellow caution triangle and flashing Fuel icon all the time.

So this weekend I pulled the plug for the fuel sender intending to short out the leads with an appropriate level resistance to fool the instruments into believing the tank is always full. There are four wires going into the sending unit: green/blue, green/red, brown/blue, brown/green. The brown ones seem to be ground. The green ones show no DC voltage when the ignition is on. What’s going on here? Is the oscillator for the capacitive sensor separate from the fuel sender unit, thus it's AC rather than DC to the sender unit? If so, is it possible to put a capacitor across the right leads to mimic a full tank? Why the ground leads?

Anyone have any ideas on how to proceed?
Have you checked with your dealer on getting BMW to replace the strip out of warranty? According to Max BMW in Troy, NY BMW is aware of the issue and you might be able to get BMW to step up. It never hurts to ask...

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Jeff Guntert - Schenectady, NY
2008 K1200GT
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post #7 of 19 (permalink) Old Jun 13th, 2011, 10:57 am
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Quote:
Originally Posted by NikonJeff
Have you checked with your dealer on getting BMW to replace the strip out of warranty? According to Max BMW in Troy, NY BMW is aware of the issue and you might be able to get BMW to step up. It never hurts to ask...
Totally agree Jeff but I too, would like this puzzle solved so I can invoke the same fix as emzed suggests. I have a feeling with the ethanol poison we're introducing in to our tanks this issue for the K12/13 bikes is going to get worse over time. And don't know about you but I won't be buying a new K1600GT for a year or so and definitely not before a GS-911 is available for that bike.

I also rely on the trip odometer even with a fuel strip that was just replaced under warranty. What I won't be able to deal with is looking at the yellow caution triangle when it next goes south on me...
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post #8 of 19 (permalink) Old Jun 13th, 2011, 12:29 pm
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Quote:
Originally Posted by dpancerz
Totally agree Jeff but I too, would like this puzzle solved so I can invoke the same fix as emzed suggests. I have a feeling with the ethanol poison we're introducing in to our tanks this issue for the K12/13 bikes is going to get worse over time. And don't know about you but I won't be buying a new K1600GT for a year or so and definitely not before a GS-911 is available for that bike.

I also rely on the trip odometer even with a fuel strip that was just replaced under warranty. What I won't be able to deal with is looking at the yellow caution triangle when it next goes south on me...
Agreed. My 2008 K1200GT has less than 7k on the clock and the fuel strip was replaced once before I bought the bike this spring and I just had it done within the first 1,000 miles I put on it!

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Jeff Guntert - Schenectady, NY
2008 K1200GT
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post #9 of 19 (permalink) Old Jun 14th, 2011, 2:12 am
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Me too.

My fuel strip just crapped out, my 08 has just gone over 3000 miles (I bought it with 1100 a few months ago). But in my case, it never triggers an alarm because it always has at least 3/4 of a tank, including when it's actually bone dry. Oops. Thankfully it happened in the driveway on the way out.

My factory warranty just ran out, but I have a 3-year extended as well.

There must be a way to permanently correct the problem. The world is full of fuel gauges that work. Maybe a home-brew copy of the stock strip made with different materials is the answer. They're failing for a reason, but there seems to be two different failure modes. One that says "empty" and triggers the alarm, and one that says "full" all the time. What exactly is failing in each case?
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post #10 of 19 (permalink) Old Jun 28th, 2011, 5:19 pm Thread Starter
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Update: Told the bike shop and BMW replaced the fuel strip for free. While the bike is long out of warranty, the part was less than a year old, so it was covered under its own warranty. I believe the mechanic's parting words were, "We'll see how long this one lasts."
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