Accuracy of fuel gauge (available fuel)

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So I've done a bit of searching and have read threads where there are issues with the in-dash fuel gauge, mostly with thermister problems (blinking gauge and such).
I think my issue is more basic - the gauge appears to be working as expected: shows Full when filled up and gradually tapers off as fuel is consumed.

Last weekend, I was out scrubbing in the new Pirelli's, keeping a watch on the gauge - it eventually went into its blinking mode and informed me: 45 miles left \ 0.5 gallon fuel.
I thought to myself, "okay, let's stop for fuel, then head back to the house".

Right at that moment, the bike sputtered and died. I put it on the center stand, rocked it fore-and-aft. Took it off the center-stand, rocked it left-and-right, centered it, and attempted to fire it up and head to a fuel station. No go. Called the g\f at the house: "grab the gas can in the garage ...". About 10 minutes later, we're on the way to a station.

I know I shouldn't rely on "extreme" accuracy, but to report 1/2 gallon of fuel available?
Any one else see this anomaly ?

 

T_C

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How hard were scrubbing the sidewals on the tires?

I've run mine into the blinking zone quite a few times and always made it by watching the miles till empty.

Some folks say that if you shut it off and then re-start once it's blinking it messes with the system and rests the counter. I haven't had that problem, and think more likely the bike had gotten leaned over enough to splash the fuel around and rest the counter. but either way.. it is still an estimate.

I do know one member here that ran out of gas when he thought he had an 1/8 of a tank. Strong winds kept him heeled over while running on the slab, he cross behind some tress and then into an underpass. While the bike was running straight up... cough.. cough.. die.
 

SupraSabre

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Before gas prices started changing like crazy, I would go two days in between my gas stops. I would get down to where it was 19 miles left often and never had an issue. There were a few times were I would see the "--", but still made it a station without running out. :D

Unless your filter is really crudded up, no guess why yours would say 45 miles and then die on you. :think1:

How many gallons did it take to fill?
 
OP
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How hard were scrubbing the sidewalls on the tires?
[...]
I do know one member here that ran out of gas when he thought he had an 1/8 of a tank. Strong winds kept him heeled over while running on the slab, he cross behind some tress and then into an underpass. While the bike was running straight up... cough.. cough.. die.
Interesting.

I was running through "exit loops" like this: http://goo.gl/maps/pg3T1 (about 40 MPH)

So, the thought is the sensor in the tank got hosed up and the gauge readout on the dash was fooled, because of the constant turned-in angles?

How many gallons did it take to fill?
Actually, I didn't pay attention - I put whatever was in the gas can (1/2 gal?), then I stopped to put in about a gallon to get me home, because I wanted to do a Seafoam + fill-up (Seafoam was at the house)
.
 

Blrfl

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Last weekend, I was out scrubbing in the new Pirelli's, keeping a watch on the gauge - it eventually went into its blinking mode and informed me: 45 miles left \ 0.5 gallon fuel.
If the dash is showing any kind of estimated remaining range, you have between 1.32 and 0.5 gallons left and the number will be based on fuel consumption during the last 20 minutes of riding. If it shows dashes ("--.-"), you're below 0.5 gallons and the ECM can no longer come up with an estimate. Gory details on how the fuel gauge works are here: CLICKY.

45-50 seems about right for what you should see when you hit one bar. I've had mine down as far as 12 (not on purpose), so you shouldn't be having it conk out almost immediately. About the only scenario I could come up with to make what you saw happen is 20 minutes of high-mileage running followed immediately by a whole lot of wide-open throttle right after the gauge reached one bar, and even that would be pushing it. A bunch of lean could do it, but it still seems a little excessive.

Your bike's pretty old but doesn't have a lot of miles on it, which leads me to think that it may have spent a lot of time sitting around. I'd recommend running it down to one bar and emptying the lower tank for an inspection to see if there's crud built up on the bottom.

--Mark
 

SupraSabre

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...Your bike's pretty old but doesn't have a lot of miles on it, which leads me to think that it may have spent a lot of time sitting around. I'd recommend running it down to one bar and emptying the lower tank for an inspection to see if there's crud built up on the bottom.

--Mark
And if there is, replace the fuel filter while you have it opened up!...It's not that hard to do.
 

Scooter

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I see that you are fairly new to this bike so I've got some questions. Do you generally follow the same fueling procedure with this bike? Or do you just put in a few gallons in at a time whenever you think you are getting close to empty? The reason I ask is that I think your lower tank fuel sensor (thermocouple) is bad but there is a way of diagnosing it without pulling the tank.

I always use the same routine when I tank up. Bike on centerstand, top off tank to the same spot (bottom of filler neck), record odometer, previous tank miles, amount of gas used and the cost. Then I reset the average fuel consumption value and the A trip meter (I always use this trip meter for my tank mileage). It might sound like a lot of work but it really isn't and it allows you to get a feel for how well your bike is running during each tank. Just by reading the average fuel consumption meter I can accurately predict when my bike is going to start flashing the last bar usually to within 5 or 10 miles.

Now, the reason why I think you have a bad thermocouple is that the same thing happened to me once on the way out to a RTE and I ended up getting stuck in BFE. I had pre-calculated that I could make it into the town where the event was taking place but that I would be way down into the reserve when that happened. What I didn't count on was 1) getting a bogus routing point into my Zumo that had me routed 25 miles west of the RTE and 2) Having a bad thermocouple. In my case, I simply did not listen to my own common sense when I knew my tank mileage was getting up in the stratosphere compared to what that tank's average MPG was. One minute I was looking down and the display still showed two bars, then the next minute the bike starting to buck and wheeze and when I looked at the fuel gauge it was now showing one bar but it also was only showing the two dashes instead of a numerical value. OOPS. :(

I would recommend doing the following to see if the sensor is truly bad. Fill up you bike fully like I described above and then reset the average fuel consumption meter and reset one of your trip meters. Then the fun part, just go out and ride the bike. You don't have to do it all at once but what you are going to do is ride the bike to point where hopefully the last segment should start flashing. At this point you are probably wondering, well just how far is that? You can use the chart below to figure that out. The Trip meter value is calculated by the following formula:

(Avg. MPG + 2) * 6.18 + 20

I add 2 to the average mpg value because the average difference between calculated mpg and the average value displayed by the ST is roughly 2 mpg (my ST, ~450 tanks)

6.18 is the amount of gas you should burn to get to the point where the last segment starts to flash. I use 20 miles to determine if the sensor is bad. This gives you some room for deviations and also leaves you with about 20 miles left in the tank to find a gas station if you reach that point where the display has not started to flash the last segment.

Example: You fill up the tank and start to ride. After 200 miles you see that the average mpg value is 39.8mpg. Rounding up to 40mpg, if the fuel display hasn't switched over to the flashing single bar after riding 280 miles, you likely have a bad thermocouple in the lower tank.

Avg. MPG--Trip meter

35 -- 249
36 -- 255
37 -- 261
38 -- 267
39 -- 273
40 -- 280
41 -- 286
42 -- 292
43 -- 298
44 -- 304
45 -- 310
46 -- 317
47 -- 323
48 -- 329
49 -- 335
50 -- 341

If you don't trust my numbers you could always bring a small gas can along with you...
 

Tom Mac 04a

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Once you get into the level of the "mile count down " it has always been fairly accurate based on your last computed mpg. If you start riding hard your mpg will drop, but I mean from like 42mpg to 25mpg.
IF all is working well on yr gauge,... What i really think what happen is that you reset the 'count-down' without knowing. I know if your in 'count-down' miles and you shut off the bike, next time on it will go back to the the higher miles left like when it originally started...

But, I don't really worry about the gauge at all... go 200 miles on the odo and fill/reset odo. By then my butt is sore enough for a walk-around.
 
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If you don't trust my numbers you could always bring a small gas can along with you...
I have a 1.5 litre version of this:

This holds about 1/3 of a gallon - enough to travel a short way in an emergency.
One option for holding twice as much fuel would be 2 of these.
 
OP
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If the dash is showing any kind of estimated remaining range, you have between 1.32 and 0.5 gallons left and the number will be based on fuel consumption during the last 20 minutes of riding. If it shows dashes ("--.-"), you're below 0.5 gallons and the ECM can no longer come up with an estimate. Gory details on how the fuel gauge works are here: CLICKY.

Your bike's pretty old but doesn't have a lot of miles on it, which leads me to think that it may have spent a lot of time sitting around.
Thanks Mark. The previous owner had purchased a 2008 ST and his other bike (the one I now own) probably sat for 2\3 of months (Nov - Feb).
And thanks for the STWiki article on how the gauge works - I've printed it out.


I see that you are fairly new to this bike so I've got some questions. Do you generally follow the same fueling procedure with this bike? Or do you just put in a few gallons in at a time whenever you think you are getting close to empty? The reason I ask is that I think your lower tank fuel sensor (thermocouple) is bad but there is a way of diagnosing it without pulling the tank.
As a rule, when the gauge reads "one bar", I stop to fill it (center-stand) to the "aluminum bar" that partially transverses [just below] the filler neck.

[snipped]
The Trip meter value is calculated by the following formula:
(Avg. MPG + 2) * 6.18 + 20
I've printed out your explanation\formula\matrix and will keep in in the fairing pocket for quick reference and apply your method - thanks!

[snipped]
But, I don't really worry about the gauge at all... go 200 miles on the odo and fill/reset odo. By then my butt is sore enough for a walk-around.
Sounds reasonable. If I know I'll be in town and will eventually fill up, I'll go to one bar and fill up.
If I'm on a jaunt and not exactly sure which town has good gas, I'll fill up when I get to 200-224 miles on the trip.

I''ll assume for now that I was already low on fuel and tossing the bike left-and-right and a bit of aggressive throttle messed with the computer's calcs.

Thanks for the all the great responses !
 
OP
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This morning's fill up (on center stand, filled to the 'aluminum bar' that transverses [just below] the filler neck.):
5.938 gals ... the final (extreme left) "bar" on the dash was flashing.

What's odd is when I fired up the bike after fill-up, all the gauge's bars lit up except the extreme right "bar" (although it did light up momentarily), as if it's not filled up all the way. It also lit up after I made a left hand u-turn and then straightened up, but then it extinguished again.

Does this suggest that the float in the upper tank is goofed? Or something with the computer how it decides how many bars to light up?
 

v8-7

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It's probably just a minor adjustment on the upper sender and won't affect anything else .

There is a remote chance that it could be a slow filing lower tank due to a clogged breather tube or slightly restricted pipe between the upper and lower tank . Easy way to eliminate this as a problem is to fill the tank , wait a few minutes and recheck the fuel level in the tank.

about 30-40 miles after the the fuel level goes to 2 bars, the ecu should start the ~ 50 mile remaining countdown. Is your bike doing that ?

Mark has an excellent description of how the fuel gauges work on the Wiki site.
 
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OP
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There is a remote chance that it could be a slow filing lower tank due to a clogged breather tube or slightly restricted pipe between the upper and lower tank . Easy way to eliminate this as a problem is to fill the tank , wait a few minutes and recheck the fuel level in the tank.
Great suggestion - i hadn't considered that.

about 30-40 miles after the the fuel level goes to 2 bars, the ecu should start the ~ 50 mile remaining countdown. Is your bike doing that ?

Mark has an excellent description of how the fuel gauges work on the Wiki site.
Yea, I've glanced at that doc on the Wiki.

And yes, I do see the countdown.

I had, at one point, lifted the tank to gain access to the airbox. After securing the tank, and fired up the bike, I noticed an improvement in engine performance (either a line was previously pinched or a there was a vacuum leak and moving the tank up/down resulted in clearing up the issue):
https://www.st-owners.com/forums/showthread.php?135648-Engine-idle-and-hesitation-improves-by-lifting-the-tank&highlight=

This evening, I should take the seat off and raise the tank and check all the lines. It's been suggested I should run to dry, then open up the lower tank and take a look inside.
 

T_C

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The other day I ran mine down to where the mileage countdown even stopped. (Below 20 miles estimated. )

Two things I learned:
1) took seven gallons to fill, so probably still had some range.
2) the estimated range once you get to the last bit is not a 'fixed' number based on your avg mpg at the time of when you hit the last mark. As my speed changed lower (and my rate of using fuel) my estimated miles remaining increased. So the computer is tracking and recalculating the whole time. I opened up the th throttle a bit in a lower gear and the estimated dropped. Upped the gear and did a more efficient cruise and my estimated increased.

Interesting....

But better to not push my luck on estimated.
 
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I ran OUT of gas once while climbing a mild hill on my way to get fuel. Blamed it on the count-down thing resetting at power off.
Not fun to push this bike up any inclined road, that's for sure!

At the station, it only took 7.1 gals.
I thought perhaps the fuel pump was taking up a half gallon of volume, but reading about other's experiences has led me to think there is tolerance in the pickup or something.
It may be worth purposefully running out just to see how far you can go, providing you keep an extra gallon with you of course.
 
OP
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There is a remote chance that it could be a slow filing lower tank due to a clogged breather tube or slightly restricted pipe between the upper and lower tank . Easy way to eliminate this as a problem is to fill the tank , wait a few minutes and recheck the fuel level in the tank.
Well, what do you know ... I finally lifted the tank last night to double-check on things ... check out the upper-to-lower-tank hose (creased).

Is it possible this hose as been replaced and it's the rwong hose?:

utol-hose.jpg

Side note ... I filled up yesterday ... 6.1 US gallons ... trip odometer showed 178 miles :(
 

v8-7

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Looks like a stock hose and they do tend to crease with the tank lifted .

The stock hose has 2 different sizes on the ends so it's unlikely it isn't the right hose .

On the other hand your gas mileage is under 30 mpg and it should be ~40 .

Are you getting 3 bars on the engine temp gauge ?
 

970mike

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Looking at that picture you have a problem. That is the reason I pull the tank completely off when I need to do anything under the tank. I would replace the fuel hose and clamps.
 

T_C

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It appears that the house woudl be straightened out when you drop the tank back down, maybe place a cmaera in there to see it when you do, just to make sure.

But that hose just lets the gas flow down to the lower tank, one of the smaller hoses is what brings the air back out as the gas flows down. I'd be checking them and make sure they are not kinked/clogged.

And yes.. your mileage is sucking, compared to most commuters, now if you are frequently drag racing, canyon carving or high speed (80mph) cruising maybe not. 3 bars on the temperature gauge?
 

BakerBoy

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Well, what do you know ... I finally lifted the tank last night to double-check on things ... check out the upper-to-lower-tank hose (creased).

Is it possible this hose as been replaced and it's the rwong hose?:

utol-hose.jpg

Side note ... I filled up yesterday ... 6.1 US gallons ... trip odometer showed 178 miles :(
I see several things...
  • Looks to me your ground wires are bent in unusual ways, possibly pressing into that hose when the tank is lowered
  • It looks like there's something else (another hose?) below that fuel hose. There should be nothing pressing on that large hose.
  • It looks like the fuel hose was installed with a twist--it can't help but kink when the tank is raised.

I also wonder if the tank air equalization lines (tank-to-tank vent) and vapor line to the evap canister drain hoses are connected properly on the underside of the tank. See my pic below to see proper connection.

I'd replace that large hose and clamps if it were mine.

 
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