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Discussion Starter #1
The fuel gauge on my EGC pulled the old "stay on full for 100 miles and then drop like a rock" trick. I know that you use the odometer, but I was interested to see if I could get it to work a little bit better.

I did a little bit of research and discovered that the gauge reads full at 10 ohms resistance and empty at 73. My tank had burned just less than 2 gallons from full and it was still sending a 10 ohm signal from the sending unit.

So, I went to RadioShack and picked up a pack each of .5W 10 ohm resistors and 5 ohm resistors. After a little bit of experimentation, I learned that a single 10 ohm resistor would adjust the fuel gauge down to about 5/8 of a tank. I think that is about right.

I took the bike out and rode it about 40 miles, and the gauge dropped to just below a half tank. 40 miles would be about a gallon, so it looks like it is tracking fairly true.

I stopped when I got back and filled the tank back up to the top. It is just shy of going all the way back up to full. But, since you can't get the tank completely full sitting on the Jiffy stand, maybe it's actually pretty close.

I know that the fuel gauge sending unit is not linear in its output. So, I somewhat expect it to behave a bit erratically when it gets down to the last quarter or so of a tank just like it did before. But, it is certainly better than it was.

I will run a few tanks through and see how it behaves. Then I can report back in case anyone is interested.

For the record, my bike is a 2005. I believe that the resistance values for the newer gauges are different.




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Mississippi Cajun
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24,018 Posts
I've monitored the gauges on several bikes over the last few years and they are all screwy. My present bike with gauge and alert lights and speedo indicators showed me to be fumes minus at 205 miles and when I filled up, I still had close to a gallon of gas left assuming this tank is really 6 gallons. But...if this is the worst problem I have to deal with, ....well, I can deal with it.
From an engineering perspective...Chas, you seem to be onto something that MOCO needs to look at.
 

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the v-rod gauge was awful. i watched as the gauge dropped from 3/4 to empty in about 10 miles. i thought i blew a fuel line. i made a bee line for the nearest station and then watched as the tank apparently refilled itself along the way. i got to the station and put just over a gallon in a 5 gallon tank....thanks MoCo, great instrumentation you have provided on these premium priced machines...

kgb
 

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Hit it she goes boom
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Mine's goofy toward the end of the tank, seems to read just fine for 4 gallons but when I get down to the last gallon (when the light should go on) sometimes is does, sometimes it doesn't. I use the odometer, so I haven't been burned yet. 03 5 gal tank.
 

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My `04 fuel gauge reads full until the tank is just about half empty, then tracks fairly well to empty...so it's a half tank gauge. The odometer is my friend.
 

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05 and my gauge is screwy too. I use the odmeter for better accuracy. Oh and that's after the fog dries up and I cAn read it.
You would think a 20 thousand dollar motorcycle would have gauges that were worth half a squirt. I guess that's what you get when you buy products from the lowest bidders to maximize your profit margin.
 

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Discussion Starter #12
Are the instruments made in China or someplace like that? I've not tore in to mine deep enough to know.
It's not the gauge itself. At least it isn't in my case.

The gauge is supposed to read full at 10 ohms resistance and empty at 73 ohms. I pulled the lead from the sending unit and replaced it with varying combinations of resistors in series (just clipped up for testing) and the gauge was full at 10 and empty at 73 (I used 75 as I only had 5 and 10 ohm resistors) A few values in between showed it at various places. So, I think the gauge is fine.

I believe it is the sending unit. In my case, I had two gallons of fuel gone from the tank and the resistance value off the sending unit was still only about 9 ohms. Based on my tests, it should have been around 20 or so.

BTW, I haven't ran the tank down really low yet to see how it behaves, but for the most part, my "mod" seems to make the gauge considerably more accurate than before.

The only thing I that is a little stinky is that it only reads about 7/8 of a tank or so with it completely full of fuel. And it catches up at about a 1/2 tank or so. It isn't ideal. But, if it tracks decent from 1/2 down to empty, it is significantly better than before.
 

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Discussion Starter #13
My `04 fuel gauge reads full until the tank is just about half empty, then tracks fairly well to empty...so it's a half tank gauge. The odometer is my friend.
It sounds like yours would respond to this mod in a similar way. That is exactly how mine behaved before.
 

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Are the instruments made in China or someplace like that? I've not tore in to mine deep enough to know.
Dresser fairing mount fuel gauges are made in Malaysia.
$(KGrHqZHJC!E7zBE+CK(BPFzRh2uTQ~~60_58.jpg


Gas tank mounted fuel gauges are made in Japan.
$T2eC16J,!ykE9s7twBIqBRoq7Grl7w~~60_57.jpg

But it's not the gauge that is the problem as Chas points out.


Seems to be the fuel sending unit that people have problems with.


Those are made in Mexico.
$(KGrHqZ,!mIFBD6TbvzeBRgB,WQtQg~~60_57.jpg
 

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Discussion Starter #15
So when I got to work this morning I had about 155 miles on the tank. I am pretty steady at 38 mpg or +/- 1, so that would put me real close to 4 gallons used.

The gauge still reads around 3/16ths of a tank. Ideally, I think it should be pretty close to empty or at least below an 1/8th of a tank if you consider the "reserve."

So, while it helps some, I think I can do better. I have another idea that I think might work even better, but I am still thinking it through.

More reporting to come.

And, yes, I am being needlessly anal about this. It isn't so much that I care about a fuel gauge but more the challenge of figuring it out and making it work.
 

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Newbie 1Oct2010
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Chasarms -- where did you install the resistors? Back side of Gauge or in the wiring that comes from the Fuel tank and runs under the console?
 

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I have learned not to trust the range indicator that shows how far til empty! Mine counts down by 10's!!! Fuel light comes on, HUNT GAS NOW!!!!
 

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I once was offered a ride in a biplane. The wings were fabric covered, and the gas guage was a twisted, flat metal strip with the bottom end stuck into a large cork. The upper end extended through a narrow hole in the top of the cowling. The length of the metal strip that showed through the cowling indicated the level of gas in the tank. I declined the offer of a ride.

af
 
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