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post #1 of 33 Old Jul 18th, 2014, 9:03 pm Thread Starter
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Stoopid fuel gauge

After my second fill up today, I got to thinking about my flaky fuel gauge. I believe that if I place a properly sized resistor or rheostat across the plug connections to the sending unit I could prove the wiring and gauge. I just want the da*n thing to work. Anyone have the resistance values?

Robert

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post #2 of 33 Old Jul 19th, 2014, 6:34 am
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Re: Stoopid fuel gauge

you might of bent the tube inside the filler neck, this stops the float from moving up and down, do you hold the nozzle when filling the tank or let it hang?, unfortunately the best way to check the sender unit it is to take it out of the tank and bench test it with an ohm meter, if the tube is damaged a broom handle inserted is close to the right size to straighten it
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post #3 of 33 Old Jul 19th, 2014, 6:48 am Thread Starter
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Re: Stoopid fuel gauge

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Originally Posted by Axle View Post
you might of bent the tube inside the filler neck, this stops the float from moving up and down, do you hold the nozzle when filling the tank or let it hang?, unfortunately the best way to check the sender unit it is to take it out of the tank and bench test it with an ohm meter, if the tube is damaged a broom handle inserted is close to the right size to straighten it
Linton
Thanks, Linton. Been there, done that. No help. I want to be able to prove that the dash gauge is good or bad. The sending unit appears to work but I don't know what resistances I should be reading.

Robert

They that can give up essential liberty to obtain a little temporary safety deserve neither liberty nor safety.
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2000 K1200LT "Latifah"
1994 R1100RSL (wife's)
1981 R80GS
1976 R90S
1965 R80/2 Frankenbike (wife's)
2001 Bunkhouse LX (given to son)
2011 Bunkhouse Queen

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post #4 of 33 Old Jul 19th, 2014, 11:47 am
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Re: Stoopid fuel gauge

I went and checked my spare unit but I could not get a reading with the ohm meter - it was all over the place. I'll take it apart today and see what I find. I thought I had measured it once before but for some reason I can't now.

John
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post #5 of 33 Old Jul 19th, 2014, 5:05 pm Thread Starter
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Re: Stoopid fuel gauge

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Originally Posted by jzeiler View Post
I went and checked my spare unit but I could not get a reading with the ohm meter - it was all over the place. I'll take it apart today and see what I find. I thought I had measured it once before but for some reason I can't now.
Thanks John. All I need is a starting point. Is a dead short equal to a full tank or empty? Or is there some BMW logic requiring a set resistance to equal full or empty?

Robert

They that can give up essential liberty to obtain a little temporary safety deserve neither liberty nor safety.
Benjamin Franklin (1706 - 1790)


2000 K1200LT "Latifah"
1994 R1100RSL (wife's)
1981 R80GS
1976 R90S
1965 R80/2 Frankenbike (wife's)
2001 Bunkhouse LX (given to son)
2011 Bunkhouse Queen

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post #6 of 33 Old Jul 19th, 2014, 6:27 pm
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Re: Stoopid fuel gauge

OK I had a flaky alligator clip. Empty is 77 ohms and full is 6 ohms.

John
2009 K1300GT Red Rocket
2009 R1200GS (Gone)
2005 K1200LT Ocean Blue Blue Wizard 110 K and counting...
2006 Bushtec Turbo+2 Spell
2004 330 Ci Convertable
K4AN

Have ridden a Motorcycle in all 48
But lack DE, MA, RI and CT with the 2005 LT

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post #7 of 33 Old Jul 19th, 2014, 6:45 pm Thread Starter
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Re: Stoopid fuel gauges

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Originally Posted by jzeiler View Post
OK I had a flaky alligator clip. Empty is 77 ohms and full is 6 ohms.
Great! Thanks John. I will "liberate" a 10 ohm resistor from work for testing purposes.

Robert

They that can give up essential liberty to obtain a little temporary safety deserve neither liberty nor safety.
Benjamin Franklin (1706 - 1790)


2000 K1200LT "Latifah"
1994 R1100RSL (wife's)
1981 R80GS
1976 R90S
1965 R80/2 Frankenbike (wife's)
2001 Bunkhouse LX (given to son)
2011 Bunkhouse Queen

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post #8 of 33 Old Jul 20th, 2014, 12:47 pm Thread Starter
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Re: Stoopid fuel gauge

I just had another thought. Since my fuel gauge shows zero, what triggers the low fuel light? Apparently not the sending unit.

Robert

They that can give up essential liberty to obtain a little temporary safety deserve neither liberty nor safety.
Benjamin Franklin (1706 - 1790)


2000 K1200LT "Latifah"
1994 R1100RSL (wife's)
1981 R80GS
1976 R90S
1965 R80/2 Frankenbike (wife's)
2001 Bunkhouse LX (given to son)
2011 Bunkhouse Queen

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post #9 of 33 Old Jul 20th, 2014, 12:55 pm
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Re: Stoopid fuel gauge

Quote:
Originally Posted by Scouter-50 View Post
I just had another thought. Since my fuel gauge shows zero, what triggers the low fuel light? Apparently not the sending unit.

Robert
Hi Robert.

I think it does activate the fuel low light and that might imply that the problem might be somewhere other than the sending unit.

Ron


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2003 LTE 164,188 miles Silver (Purchased with 1687)
2008 R1200RT 176,196 miles (Purchased with 16458)
2017 R1200RT 96,669miles (new)
Total BMW miles 509,508
1982 GL1100 rode 84108 miles (bought with 12012 sold 96120)
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post #10 of 33 Old Jul 20th, 2014, 2:26 pm
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Re: Stoopid fuel gauge

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Originally Posted by Scouter-50 View Post
I just had another thought. Since my fuel gauge shows zero, what triggers the low fuel light? Apparently not the sending unit.

Robert
Inside the relays electrical junction box (under fuel tank) there is a "Fuel-Warning-Control-Unit". Although it sitting near all other relays, this one is a lot smarter than an ordinary relay (and a lot more $$$).

I never fully opened this fuel-warning-unit, but from the BMW electrical-diagrams, you get these hints (available on CD from BMW, not from CLYMER)
(1) Fuel-Warning-Control-Unit has 5 pins being used by BMW
(2) Fuel level sender (float inside tank) has 1 wire for ground (brown wire) and another wire signal being fed to gauge and also to Fuel-Warning-Control-Unit (yellow-violet wire)
(3) Another pin of the Fuel-Warning-Control-Unit is for ground (brown wire)
(4) Another pin of the Fuel-Warning-Control-Unit is to light up the Low-fuel warning on dash (White-Green wire)
(5) Another pin of the Fuel-Warning-Control-Unit is for power and is fed from FUSE #1 which also feed instruments. Fuse #1 is only valid for 1999-2004 models (Green-black wire)
(6) Finally, the last pin of the Fuel-Warning-Control-Unit goes into pin #3 of the diagnostic connector for dealer's computer or GS911 (Brown-Black wire). You will understand better this part if you read this from the GS911 folks: http://www.hexcode.co.za/techinfo/ta...n-ma2.4-models

So based on this info, my assumption is that:
(a) The Fuel-Warning-Control-Unit is the one controlling the dash "low-fuel" warning lamp.
(b) The Fuel-Warning-Control-Unit has some kind of static memory as it can remember the fuel setting value for "low-fuel" even if Battery is unplugged for weeks.
(c) Electrical diagram shows than none of these input-outputs goes to BOSH-Motronic unit. This makes the assumption in (b) above very plausible.

I hope this helps...
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post #11 of 33 Old Jul 20th, 2014, 8:57 pm Thread Starter
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Re: Stoopid fuel gauge

Quote:
Originally Posted by sailor View Post
Inside the relays electrical junction box (under fuel tank) there is a "Fuel-Warning-Control-Unit". Although it sitting near all other relays, this one is a lot smarter than an ordinary relay (and a lot more $$$).

I never fully opened this fuel-warning-unit, but from the BMW electrical-diagrams, you get these hints (available on CD from BMW, not from CLYMER)
(1) Fuel-Warning-Control-Unit has 5 pins being used by BMW
(2) Fuel level sender (float inside tank) has 1 wire for ground (brown wire) and another wire signal being fed to gauge and also to Fuel-Warning-Control-Unit (yellow-violet wire)
(3) Another pin of the Fuel-Warning-Control-Unit is for ground (brown wire)
(4) Another pin of the Fuel-Warning-Control-Unit is to light up the Low-fuel warning on dash (White-Green wire)
(5) Another pin of the Fuel-Warning-Control-Unit is for power and is fed from FUSE #1 which also feed instruments. Fuse #1 is only valid for 1999-2004 models (Green-black wire)
(6) Finally, the last pin of the Fuel-Warning-Control-Unit goes into pin #3 of the diagnostic connector for dealer's computer or GS911 (Brown-Black wire). You will understand better this part if you read this from the GS911 folks: http://www.hexcode.co.za/techinfo/ta...n-ma2.4-models

So based on this info, my assumption is that:
(a) The Fuel-Warning-Control-Unit is the one controlling the dash "low-fuel" warning lamp.
(b) The Fuel-Warning-Control-Unit has some kind of static memory as it can remember the fuel setting value for "low-fuel" even if Battery is unplugged for weeks.
(c) Electrical diagram shows than none of these input-outputs goes to BOSH-Motronic unit. This makes the assumption in (b) above very plausible.

I hope this helps...

Thanks, John. The interconnecting of components sounds like BMW. I think I will try to burn enough fuel to make the light come on just to see if it works. Hopefully I don't get stranded. I remember someone saying the factory setting was at the one gallon mark. Hopefully they are right and the previous owner never reset it. Probably not, since he did not work on the bike and I bought it with less than 8K miles.

Robert

They that can give up essential liberty to obtain a little temporary safety deserve neither liberty nor safety.
Benjamin Franklin (1706 - 1790)


2000 K1200LT "Latifah"
1994 R1100RSL (wife's)
1981 R80GS
1976 R90S
1965 R80/2 Frankenbike (wife's)
2001 Bunkhouse LX (given to son)
2011 Bunkhouse Queen

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post #12 of 33 Old Jul 21st, 2014, 12:12 pm
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Re: Stoopid fuel gauge

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Originally Posted by Scouter-50 View Post
Thanks, John. The interconnecting of components sounds like BMW. I think I will try to burn enough fuel to make the light come on just to see if it works. Hopefully I don't get stranded. I remember someone saying the factory setting was at the one gallon mark. Hopefully they are right and the previous owner never reset it. Probably not, since he did not work on the bike and I bought it with less than 8K miles.

Robert
Be careful with that, the LT is a heavy beast to push to the gas station when it runs dry - not an experience I ever want to repeat. You might want to carry a small can with a gallon in it when you start getting low just to save yourself some sweat.

-Steve

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post #13 of 33 Old Jul 21st, 2014, 12:44 pm
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Re: Stoopid fuel gauge

Robert,

I do have a spare instrument panel if you want to try it out.

Dan M.
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post #14 of 33 Old Jul 31st, 2014, 8:52 pm Thread Starter
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Re: Stoopid fuel gauge

Update. I filled up today in South Dakota after stretching my range and put in 6.33 gallons. I had no lights or warnings. What gives?

Robert

They that can give up essential liberty to obtain a little temporary safety deserve neither liberty nor safety.
Benjamin Franklin (1706 - 1790)


2000 K1200LT "Latifah"
1994 R1100RSL (wife's)
1981 R80GS
1976 R90S
1965 R80/2 Frankenbike (wife's)
2001 Bunkhouse LX (given to son)
2011 Bunkhouse Queen

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post #15 of 33 Old Jul 31st, 2014, 9:02 pm
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Re: Stoopid fuel gauge

You were pretty luck as you were about on fumes. Maybe its time for a new (used) fuel sender. Where was the fuel gauge at the time of fill up?

John
2009 K1300GT Red Rocket
2009 R1200GS (Gone)
2005 K1200LT Ocean Blue Blue Wizard 110 K and counting...
2006 Bushtec Turbo+2 Spell
2004 330 Ci Convertable
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But lack DE, MA, RI and CT with the 2005 LT

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post #16 of 33 Old Jul 31st, 2014, 11:29 pm
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Re: Stoopid fuel gauge

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Update. I filled up today in South Dakota after stretching my range and put in 6.33 gallons. I had no lights or warnings. What gives?

Robert
Mine is doing the same thing, I just added 6.25 gallons the other day with ho low fuel light and the gauge was reading about 1/4 tank. It goes up to full when filled, I cannot decide if it is worth tearing my hair out trying to fix or not! Please let me know if you get to the root of the problem.
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post #17 of 33 Old Aug 1st, 2014, 1:43 am
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Re: Stoopid fuel gauge

Could be a bad ground

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post #18 of 33 Old Aug 1st, 2014, 7:31 am Thread Starter
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Re: Stoopid fuel gauge

Quote:
Originally Posted by jzeiler View Post
You were pretty luck as you were about on fumes. Maybe its time for a new (used) fuel sender. Where was the fuel gauge at the time of fill up?
John, the fuel gauge was showing empty for most of that tank. When I fill up the gauge goes up to about 1/2-3/4 for about 10 miles or so then drops to zero for the rest of the tank.

Robert

They that can give up essential liberty to obtain a little temporary safety deserve neither liberty nor safety.
Benjamin Franklin (1706 - 1790)


2000 K1200LT "Latifah"
1994 R1100RSL (wife's)
1981 R80GS
1976 R90S
1965 R80/2 Frankenbike (wife's)
2001 Bunkhouse LX (given to son)
2011 Bunkhouse Queen

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post #19 of 33 Old Aug 1st, 2014, 7:34 am Thread Starter
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Re: Stoopid fuel gauge

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Could be a bad ground
Thanks, but where would the ground point be?

Robert

They that can give up essential liberty to obtain a little temporary safety deserve neither liberty nor safety.
Benjamin Franklin (1706 - 1790)


2000 K1200LT "Latifah"
1994 R1100RSL (wife's)
1981 R80GS
1976 R90S
1965 R80/2 Frankenbike (wife's)
2001 Bunkhouse LX (given to son)
2011 Bunkhouse Queen

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post #20 of 33 Old Aug 1st, 2014, 7:56 am
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Re: Stoopid fuel gauge

You have 2 separate devices, an indicator and a gauge, both controlled by a single wire from the fuel sending unit and both not indicating correctly. Symptoms point to a faulty sending unit. Assuming a resistance range of 6-77 ohm buy a $4 100 ohm pot and simulate the sending unit. You also have open and short for additional information, I assume an open will compare with 77 ohm and a short with 6.


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post #21 of 33 Old Aug 1st, 2014, 3:43 pm Thread Starter
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Re: Stoopid fuel gauge

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Originally Posted by Enduro View Post
You have 2 separate devices, an indicator and a gauge, both controlled by a single wire from the fuel sending unit and both not indicating correctly. Symptoms point to a faulty sending unit. Assuming a resistance range of 6-77 ohm buy a $4 100 ohm pot and simulate the sending unit. You also have open and short for additional information, I assume an open will compare with 77 ohm and a short with 6.
Sounds like a plan when I get home. We're in Platte City MO at the moment getting a late lunch.

Robert

They that can give up essential liberty to obtain a little temporary safety deserve neither liberty nor safety.
Benjamin Franklin (1706 - 1790)


2000 K1200LT "Latifah"
1994 R1100RSL (wife's)
1981 R80GS
1976 R90S
1965 R80/2 Frankenbike (wife's)
2001 Bunkhouse LX (given to son)
2011 Bunkhouse Queen

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post #22 of 33 Old Aug 1st, 2014, 3:56 pm
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Re: Stoopid fuel gauge

Quote:
Originally Posted by Enduro View Post
You have 2 separate devices, an indicator and a gauge, both controlled by a single wire from the fuel sending unit and both not indicating correctly. Symptoms point to a faulty sending unit. Assuming a resistance range of 6-77 ohm buy a $4 100 ohm pot and simulate the sending unit. You also have open and short for additional information, I assume an open will compare with 77 ohm and a short with 6.
According to sailors post #10 above.
I would replace the sending unit also.

Good Luck...Randy
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post #23 of 33 Old Aug 1st, 2014, 5:17 pm
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Re: Stoopid fuel gauge

Robert, I had to fix the sending unit on mine when I got it. Was doing the same as yours. As I recall I used a framing square clamped into a vise and a plastic mallet to straighten the aluminum tube. The other issue was a nut on the tube assembly that is part of the circuit. I think the tube was loose on it's base and the nut was loose causing intermittent readings. All that thing consists of is a float with contact points that slides up and down a u-shaped piece of ni-chrome wire. The only thing that can normally go wrong with it is getting stuck or getting a loose connection. I bet you can fix it if you give it a look.


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post #24 of 33 Old Aug 1st, 2014, 7:19 pm
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Re: Stoopid fuel gauge

If you want to swing by North Alabama I have a spare we can stick in...

John
2009 K1300GT Red Rocket
2009 R1200GS (Gone)
2005 K1200LT Ocean Blue Blue Wizard 110 K and counting...
2006 Bushtec Turbo+2 Spell
2004 330 Ci Convertable
K4AN

Have ridden a Motorcycle in all 48
But lack DE, MA, RI and CT with the 2005 LT

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post #25 of 33 Old Aug 1st, 2014, 8:02 pm
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Re: Stoopid fuel gauge

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Originally Posted by Scouter-50 View Post
Thanks, but where would the ground point be?

Robert
Like most systems the power goes into your gauge, from there to sending unit from sending unit to ground. The resistance to ground is what feeds the gauge. If you took the wire from the gauge to the sending unit and shorted it to ground the gauge will show full. So resistant gets higher as fuel goes down. With temperature gauge the sending unit is high resistance when cold and reduces as engine temp increases.

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post #26 of 33 Old Aug 1st, 2014, 10:28 pm Thread Starter
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Re: Stoopid fuel gauge

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If you want to swing by North Alabama I have a spare we can stick in...
Thanks for the offer John. I am in Nevada Missouri tonight and will be in North Texas tomorrow night.

They that can give up essential liberty to obtain a little temporary safety deserve neither liberty nor safety.
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2000 K1200LT "Latifah"
1994 R1100RSL (wife's)
1981 R80GS
1976 R90S
1965 R80/2 Frankenbike (wife's)
2001 Bunkhouse LX (given to son)
2011 Bunkhouse Queen

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post #27 of 33 Old Aug 1st, 2014, 10:31 pm Thread Starter
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Talking Re: Stoopid fuel gauge

Thanks for all the ideas. I will post my findings when I rip the clothes of the b*tch when I get home. I will be gentle.

Robert

They that can give up essential liberty to obtain a little temporary safety deserve neither liberty nor safety.
Benjamin Franklin (1706 - 1790)


2000 K1200LT "Latifah"
1994 R1100RSL (wife's)
1981 R80GS
1976 R90S
1965 R80/2 Frankenbike (wife's)
2001 Bunkhouse LX (given to son)
2011 Bunkhouse Queen

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post #28 of 33 Old Aug 2nd, 2014, 7:09 am
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Re: Stoopid fuel gauge

You know this might be to easy for you but I just had mine apart for a gas filter ,air filter change glad I did THAT;; but my fuel gauge was doing about the same thing I looked up in the wire that goes to the fuel tube in the tank and one was tarnished up with some green shit on one the pins for sure clean them up with electcal cleaner and put electrical grease on them I am GOOD

Gary
2003 K1200LT
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post #29 of 33 Old Aug 16th, 2014, 12:23 pm Thread Starter
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Re: Stoopid fuel gauge revisited

OK guys, it looks like everyone that said sending unit wins the prize. I took some fast and nasty pics with my iPhone. pic 1 is zero ohms, pic 2 is 5.3 ohms, pic 3 is 33.8 ohms, pic 4 is 50.6 ohms and pic 5 is infinity. I measured the resistance of the sending unit and got 318 ohms, i then started tapping the top of the sending unit and the resistance kept dropping till it reached 33.3 ohms which is about what I would expect with the amount of gas that I have in the tank. I am somewhat puzzled as to what to do next. I have had the sending unit apart and cleaned the slider wires and cleaned and lubed the connections previously. I am now beginning to suspect the connections on the ni-chrome wires themselves. I believe that they are just riveted. Would it be possible to get in there to solder these connections?

Robert
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They that can give up essential liberty to obtain a little temporary safety deserve neither liberty nor safety.
Benjamin Franklin (1706 - 1790)


2000 K1200LT "Latifah"
1994 R1100RSL (wife's)
1981 R80GS
1976 R90S
1965 R80/2 Frankenbike (wife's)
2001 Bunkhouse LX (given to son)
2011 Bunkhouse Queen

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post #30 of 33 Old Aug 16th, 2014, 4:42 pm
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Re: Stoopid fuel gauge revisited

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Originally Posted by Scouter-50 View Post
OK guys, it looks like everyone that said sending unit wins the prize. I took some fast and nasty pics with my iPhone. pic 1 is zero ohms, pic 2 is 5.3 ohms, pic 3 is 33.8 ohms, pic 4 is 50.6 ohms and pic 5 is infinity. I measured the resistance of the sending unit and got 318 ohms, i then started tapping the top of the sending unit and the resistance kept dropping till it reached 33.3 ohms which is about what I would expect with the amount of gas that I have in the tank. I am somewhat puzzled as to what to do next. I have had the sending unit apart and cleaned the slider wires and cleaned and lubed the connections previously. I am now beginning to suspect the connections on the ni-chrome wires themselves. I believe that they are just riveted. Would it be possible to get in there to solder these connections?

Robert
I don't see why not, just remember the soldering iron is a heat source, and you are working around gasoline.

later..Randy

2006 LT
Magnesium Shwarz Metalic
Bountiful, Utah
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post #31 of 33 Old Aug 16th, 2014, 4:52 pm Thread Starter
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Re: Stoopid fuel gauge revisited

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Originally Posted by 2006lt View Post
I don't see why not, just remember the soldering iron is a heat source, and you are working around gasoline.

later..Randy
Minor problem.

Robert

They that can give up essential liberty to obtain a little temporary safety deserve neither liberty nor safety.
Benjamin Franklin (1706 - 1790)


2000 K1200LT "Latifah"
1994 R1100RSL (wife's)
1981 R80GS
1976 R90S
1965 R80/2 Frankenbike (wife's)
2001 Bunkhouse LX (given to son)
2011 Bunkhouse Queen

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post #32 of 33 Old Aug 16th, 2014, 8:23 pm
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Re: Stoopid fuel gauge

The low fuel relay looks very much like the one used in the R1100 series bikes. It is a differential op amp driving a transistor switch to trigger the lamp, no moving parts. It's there to stop the lo fuel lamp flashing on/off as the fuel sloshes around. I've pulled a couple of non workers apart and both had a blown transistor which when replaced got em going. It needs a steady lo fuel signal coming into it for a minute or two before it triggers.


07 R1200RTP
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post #33 of 33 Old Aug 16th, 2014, 8:33 pm Thread Starter
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Re: Stoopid fuel gauge

OK, latest update. After futzing around with the sending unit I have managed to make the riveted contacts "work". I do not trust the repair though. While messing about the ni-chrome wire broke where it was stressed at the bottom carrier spring. I made a crimp connector using a piece of # 12 copper wire with a tiny hole drilled in it. I restrung the wire and it is working (for now). It may last forever and it may quit tomorrow. I now want to replace the sending unit since I do not trust the riveted connector at the top of the sending unit. Anyone got one they would part with? PM me if you do.

Thanks for everyones input on this problem, this forum is the finest thing ever built for this bike.

Thanks again, Robert.

Tired now, it's time for wine!

Robert

They that can give up essential liberty to obtain a little temporary safety deserve neither liberty nor safety.
Benjamin Franklin (1706 - 1790)


2000 K1200LT "Latifah"
1994 R1100RSL (wife's)
1981 R80GS
1976 R90S
1965 R80/2 Frankenbike (wife's)
2001 Bunkhouse LX (given to son)
2011 Bunkhouse Queen

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