Damn fuel gauge inconsistency

[Spitfire]

So it's a typical Saturday, go for a ride into town, run errands, about 10-15 miles. Start with 3 bars. Stop after 5 miles to pull a bug out of my ear that somehow got in there when I put my earplugs in. Start it back up and down to two bars. Note to self, gas soon. A few more miles, go to pick up stuff. Restart, down to one bar. Run to the resto, grab a bite, start back up, two bars. Go watch the NBA finals, come back out, 3 bars.  And I could swear somewhere in these runs it went back up to 4 bars at one point. More erratic from 3 bars down I've noticed.

 

This is driving me batty. How much gas do I really have at any one time and why isn't it accurate and changes so much? I do allot of touring and out to no where, so fuel is critical.

Finally do fill it and doesn't even take two gallons to fill. My only complaint with the bike, wonky gas gauge. Am I the only one?

[norcal616]

nope... gas tank lvl sensors work like a charm in nice rectangular tanks, not so much in a motorcycle tank... bout 98% of us go by miles...  on another note ppl assume a "windscreen" on a motorcycle which is supposed to act/function like a car "windshield"...

[rider]

The indicated fuel level can be affected by how level the bike is.  On/off the sidestand, pointed uphill/downhilll, your weight sinking the rear, whatever else affects it.  Mostly this gets weird when the level is under about 1/2 a tank ish.

Like @norcal616said, most of us go by the odometer.  You get a pretty good feel for when it's low after awhile.

I usually fuel up at about 105 - 120 miles as that's 2 days commuting mileage for me.  Theres usually 2 or 3 bars left on the guage and it takes 2 to 2.3 gallons so I've got another gallon or so left of usable fuel.

If you're going long stretches where fuel stops can be far apart, you can carry quart/liter/litre (whatever) fuel bottles strapped to the subframe.  There's a few people on this forum that have posted pics of their setup.

@stev74made a very detailed post on the fuel level:

 

[faffi]

Personally, I have found that either the gauge is erratic - not in the way you describe, which I think have only happened once over a full year - but when it shows empty. Either that, or what I can put into the tank vary by a litre or more, because if I fill at the same spot on the gauge, what I can fill varies a lot from one time to the next. Which seems strange, since I always top up several times after the tank seems full since the level will drop a little as air escapes. Even running it virtually bone dry - it had been missing for several miles already - I was still missing just over a litre to reach the promised 14 litres.

[rick]

small tank, irregular shape, gas sloshes about - all of this makes it hard on a fuel sender. to deal with sloshing side to side and front to back, there's probably some "damping" feature built into the dash. But shut it off and restart on the sidestand, you might get a different read than it was when you shut it off as the computer resets.

 

My last BMW's fuel gauge was straight analog and the needle would swing all over the place. Stop on a hill and the level would be really different based on whether faced uphill or down. My Aprilia does none of that and neither does the FZ. 

 

IMO, it seems unlikely there's as much space inside that can as Yamaha claims. But with the excellent fuel economy, the seat is more rate limiting than the fuel in my universe.

[AlbatrossCafe]

Mine is consistent (meaning that the bars don't jump up and down), but it is definitely not linear. My first bar takes like 50 miles to go down, the next few take like 15 each, and then the last one takes like 25 lol.

 

But yeah, I just go by trip miles per tank. It's easier.

[Spitfire]

If anyone has taken off the fake tank covers, the actual real steel tank is fairly square and rectangular. Doesn't appear to be a reason for variability.

To clarify, the gauge varies at start up and restart, not while operating. It is constant while driving. No problem there. Just a different reading when I stop and then restart it, both of which are done level and upright. Flat around here.

Of course on kick stand, leaning etc but like when I am perfectly vertical, like most of the time when I am riding, shouldn't it correct? Not doing Twisties or mad lean angles, just driving down the road. And at restart, I am on the bike and level but the gauge varies a bar or two from the level it was at when I stopped it prior. And like I said, mostly when at 3 bars or less.

So I am NOT at kickstand angle when either starting or stopping. Always turn off or on when bike is upright. Just annoying and with no other comments on here, must just be mine.

Maybe it's my magnetic personality throwing it off. Or being within 5000 miles too close to magnetic North Pole. Clarkson and May have the same problem whenever they come to North America, except it affects their GPS. They're always getting lost. 

[rick]

YEah, sounds like something's not right. 

 

W/o knowing exactly how this sender is built, looks like it's a common float set-up, connected to a variable resistor with ohm readings being low with the tank full and high when it's empty. This is how my Aprilia's gauge works. After putting a new sender in the tank, it now near reads "F". Goofy gauges. 

 

you could have some corrosion or crud built up inside that resistor or maybe even the pivot for the float - our ethanol laden fuel is no good for anything. Try running some Techron or other FI cleaner in a coupe tankfuls and see if that doesn't help. 

 

Here's the ohm numbers from the service manual

 

[ducttapewd40]

I've never had a fuel gauge on a bike before this one, so I'm used to going by mileage and see the gauge as more of a luxury but it's seemed pretty consistent with the exception of going up or down a bar depending on whether or not I just stopped and it was reading while it was on the sidestand.  Plus I have a 70 mile round trip commute every day, so I end up just filling it every other day anyway.  

[rick]

Linearity across the entire tankful isn''t as important as consistency near the bottom, imo. You don't need to know when it's even half-full. Just need to know when to go get more.

 

And all you have to do is look at those specs for the sender. That 2 ohm range at the top and 6 ohms at empty are a bit more than ~ 20% variation. Bike to bike will/can be different depending on that sensor, but hopefully it'll read close to the same at whatever fuel level.

 

It's also possible that the amount of ethanol in the fuel can also have an effect. Gasoline isn't much of a conductor, but the water that comes with the ethanol sure is.

[faffi]

That's why I like a mechanical reserve; it should be consistent and then I always know how much fuel is left and, based upon the mileage, understand if the consumption is higher or lower than typical. This again allows me to calculate roughly how far I can go until reserve has gone empty.

[rick]

28 minutes ago, faffi said:

That's why I like a mechanical reserve; it should be consistent and then I always know how much fuel is left and, based upon the mileage, understand if the consumption is higher or lower than typical. This again allows me to calculate roughly how far I can go until reserve has gone empty.

And on that note, I can live w/o the gauge turning off and counting miles instead.

 

Have to admit, I've been carrying a small aluminum bottle of fuel with me since getting this bike - just cause of the small tank vol. . As soon as i stop carrying it, I'll ran the darn thing empty.

[stev74]

The tank sensor measurement is not very accurate....especially when the tank is  > 60% full.
Its getting better the less fuel is in it.
 

[Spitfire]

FYI, Completing a detailed analysis of "the gauge". To further elaborate with detail, 

 

Odometer.   Tank level

 

0mls                 3 bars

Ride around town, couple start and stops (Ign.off), consistent and logical.

 

31mls              2 bars after restart

Stopped at resto. Restart, couple short trips. Level.

 

35mls.             1 bar after pitstop (Ignition off) and restart. Read 2 bars before stopping (Ign.off). Level.

 

37mls               Empty flashing, upon restart after short trip, was reading 1 bar before turning off. Was parked on an incline making kickstand lower. Drive home, flashing E all the way.

 

 

39mls               2 bars at start up after being parked for two days, level ground.

 

As mentioned by all (thx), will be verifying total tank mileage with the odometer in future.

 

Even greater than 3 bars, have noticed that the restart tank level can vary by a bar or two lower from the previous ign shut off level. But not as radical as at lower tank level.

My previous explanation I see was not detailed enough nor properly explained for all to understand. Hopefully, this is clearer and maybe others have experienced this as well?

[Spitfire]

Rick wrote, 

 

Linearity across the entire tankful isn''t as important as consistency near the bottom, imo. You don't need to know when it's even half-full. Just need to know when to go get more.

 

Totally agree with you on this Rick, and thus the purpose of a gauge.

[Spitfire]

On 6/6/2018 at 6:52 AM, faffi said:

That's why I like a mechanical reserve; it should be consistent and then I always know how much fuel is left and, based upon the mileage, understand if the consumption is higher or lower than typical. This again allows me to calculate roughly how far I can go until reserve has gone empty.

Agreed. The only times I've ever run out of gas was with a digital gauge. Can't read reserve or empty.

[captainkool4]

I've noticed this on mine too.  The gauge will read 2 bars, then later three, then four.  It seems like when it's low though, like one bar, it doesn't hop around it stays low.

[Beemer]

The DewMan and I take local rides every week that the weather permits and not only have we noticed the same thing with the bars we've noticed how after both of us topping off with gasoline just before a ride his bike always shows one less bar than mine after we've ridden for awhile. I don't know if that's due to an inconsistent gauge or what but it seems we've both become accustomed to the gauge and can predict it fairly well.

 

All I could say as a remedy to ease your worrying is to buy a fuel bottle or two and mount them on the side of your bike. (filled of course )

 

It seems we've been down this road before, have we, anyone?

[Spitfire]

Yesterday

 

Odometer.         Tank level

40 mls.               1 bar  After restart from ign.off. level

 

Today

 

42 mls.              2 bars at startup this morning just to test. Level.

 

Btw, at flash E, what is the approx mileage left before it dies from lack of fuel? Assuming of course that the flashing E is ALWAYS at the same consistent, constant intank fuel level which I have serious doubts about now.

[DewMan]

 

8 minutes ago, Spitfire said:

Btw, at flash E, what is the approx mileage left before it dies from lack of fuel?

For my ECU flashed and aftermarket exhausted 2017, I get approx. 120 miles before E starts flashing from a full tank. This is followed by about 20 miles on "reserve" is the furthest I've taken it. I've not run it dry yet... not good for fuel pump to do so.

[dmoney]

Mine is a 2016 and the fuel gauge is pretty reasonable or at least i have figured out how to make up for its inconsistency. My E trip starts flashing at about 300km (180 ish miles) and then get about 80km (50 ish miles) before i fill up (usually about 13-13.5 litres) Thats generally what i get each week. If you compare you're average mpg, assuming you reset it after each fill up, with distance travelled you should get a much more accurate way to go about it. Check it every time you fill up and you will spot any inconsistencies

 

Edit: run akra carbon, no ecu flash

[Spitfire]

You're saying that you get 230 miles per tank? Wow, anyone else in that range?

Of course you must be maxing for mpg or l/100km which is amazing. I try to do the same thing, coast down hills, etc...

[dmoney]

Yeah on average im about there. Anything between 220 and 240 is achievable with normal riding. The best i got was about 267 (431km) but that nearly ran it dry and i filled up 13.6 litres. I used to live near a petrol station so i took my chances a bit haha

 

On my dash it usually reads about 5-6% more than actual consumption so i know when im at that level to just go fill up because ive got maybe 15-20 km before it gets a bit dicey

[Spitfire]

Hmmm, there might be a conversion factor issue there.

Imperial gallon vs US gallons.

Which are you using?

[dmoney]

I was just using litres as that is what we use in Australia. I guess you can use a simple conversion calculator and work it from there.