Fuel Reserve - is it really a reserve?

divemaster5734 said:

I called the dealer's service dept the next day and was told the level sensor "recalibrates" itself and if never run low it will have errors indicating less gas than what is actually present.

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What they told you is B.S. in my opinion.
The distance remaining to empty can and does vary. The reason that it varies is because each time that the low fuel warning is triggered, it makes a new calculation based on the fuel consumption rate at the time that the current low fuel warning was triggered. If the fuel consumption rate is different from the last time, the calculated distance to empty will vary accordingly.

The low fuel sensor is a thermistor. All it does is sense whether it is submerged in fuel or not, and send that information to the computer.
The amount of fuel that is remaining in the tank when the sensor is exposed to air is a known fixed quantity. Based on the current fuel consumption rate at the time that the sensor is exposed, the computer calculates the distance remaining to empty for that amount of fuel. From that point on it is a mathematical calculation based on distance traveled and the current fuel consumption rate. If the fuel consumption rate significantly increases or decreases for a long enough time/distance interval, the computer recalculates the distance remaining to empty based on that new consumption rate.

When enough fuel is put in to the tank to submerge the sensor again, regardless of whether you fill it or not, the computer will make the same calculation again the next time that the sensor is exposed to air. It will base that calculation on the fuel consumption rate at that time.

Still fairly new to the ST1300 but I've noticed the gauge drops from 3 bars straight to 1 bar flashing. There's never been 2 bars showing - so I need to check out the Sender unit but unsure if it's in the top or bottom tank...?
The trip is Zero'd as soon as the 1 bar flashes so I know there's roughly 40 miles to ride and find fuel.
Shame we can't convert the meter to MPGallon instead of MPLitre.

Mr.E said:

Shame we can't convert the meter to MPGallon instead of MPLitre.

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I have a July 2002 and my display shows MPG. Not sure at what point it was changed to MPL.

Rob20111 said:

Hey, I'm 60 now, I'm allowed. LOL

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Ah the kidz these days! It's all I can do to not shake my umbrella at the sky and scream "Get off my lawn!"

As mentioned many times before; your fuel pump doesn’t like a low level.Ask my swmbo.

Mr.E said:

There's never been 2 bars showing - so I need to check out the Sender unit but unsure if it's in the top or bottom tank...?

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It is in the top tank.
Some people have taken the sending unit out and successfully fixed this problem by gently cleaning the contact strip that the float uses to indicate fuel level.

I had the same problem. I filled the tank with fuel and a higher than recommended dose of SeaFoam. I did this at a time when I knew I wasn't going to be using the bike for a week. I let it sit for a week and then burned out that tank of fuel. I refueled and added a high concentration of SeaFoam and let it sit again. After I burned out the second tank of fuel, I refueled and added the remaining SeaFoam from the two bottles that had I bought. That was years ago and it has never occurred again. I think I got lucky. The SeaFoam must have dissolved some varnish on the sending unit that was causing the trouble.

Andrew Shadow said:

What they told you is B.S. in my opinion.
The distance remaining to empty can and does vary. The reason that it varies is because each time that the low fuel warning is triggered, it makes a new calculation based on the fuel consumption rate at the time that the current low fuel warning was triggered. If the fuel consumption rate is different from the last time, the calculated distance to empty will vary accordingly.

The low fuel sensor is a thermistor. All it does is sense whether it is submerged in fuel or not, and send that information to the computer.
The amount of fuel that is remaining in the tank when the sensor is exposed to air is a known fixed quantity. Based on the current fuel consumption rate at the time that the sensor is exposed, the computer calculates the distance remaining to empty for that amount of fuel. From that point on it is a mathematical calculation based on distance traveled and the current fuel consumption rate. If the fuel consumption rate significantly increases or decreases for a long enough time/distance interval, the computer recalculates the distance remaining to empty based on that new consumption rate.

When enough fuel is put in to the tank to submerge the sensor again, regardless of whether you fill it or not, the computer will make the same calculation again the next time that the sensor is exposed to air. It will base that calculation on the fuel consumption rate at that time.

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.
I agree with your logic.
I'm a Master Electrician, and understand stuff with "Sparkles".
Using a thermistor as the fuel level causes inherent reliability issues simply due to a thermistor's function as a heat sensor.
Which means it detects the liquid level as low when it is no longer submerged in the cooler petrol compared to the warmer ambient heat.
How this is processed by the I/O is probably a simple yes or no, compared to a 4-20ma current or other sensor comm methods.
I'm not even going to pretend to understand the C+ logic, and it doesn't make logical sense that running down a reserve tank would reset the parameters based on the sensor type you described aside from use and that previous tanks avg MPG.
Nonetheless, I am convinced of the effectiveness.
Yes of course there's some fuzzy logic based on operational conditions.
That said, if I don't let the reserve tank run out every so often I seem to get intermittent and sporadic results.
Most of my trips are 70 miles one way with a cruising speed around 80-90mph and traffic density determines the amount of lane splitting required.
With an accurate reserve indicator I can squeeze out two round trips.
Without "resetting" the reserve it goes into low fuel mode 40-50 miles early.
Call it superstition, I won't walk under a ladder unless I will be able to go under another one before the end of the day, because it has to balance out to even. And yes, there are a couple more, but that works for me....lol
Armed with previous trip knowledge, I have continued to run on the reserve well beyond the initial 40ish miles remaining indicator

Andrew Shadow said:

It is in the top tank.
Some people have taken the sending unit out and successfully fixed this problem by gently cleaning the contact strip that the float uses to indicate fuel level.

I had the same problem. I filled the tank with fuel and a higher than recommended dose of SeaFoam. I did this at a time when I knew I wasn't going to be using the bike for a week. I let it sit for a week so the and then burned out that tank of fuel. I refueled and added a high concentration of SeaFoam and let it sit again. After I burned out the second tank of fuel, I refueled and added the remaining SeaFoam from the two bottles that had I bought. That was years ago and it has never occurred again. I think I got lucky. The SeaFoam must have dissolved some varnish on the sending unit that was causing the trouble.

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Just learned something new.
I'll try it as the never seen two bar indicator has been a frustration for me as well.
Thanks

I'll have to check out the book.
"When all else fails" an ***** like that, instructions can be useful

I have never ridden a fuel injected bike (or driven a fuel injected car, for that matter) and thought that it actually had a reserve fuel system.

Once it's gone, it's gone. When the display gets low enough, I have a strange compulsion to put more fuel in. Only ever run out once. That was a horrible walk up the side of the M62 at 3am in the rain.

I've never run out of fuel though came slightly close once. But due to a broken key in the gas cap while attempting to refuel at my overly prudent 3-bar limit I had to walk the ST about one+ block and I never want to do that again. So I continue my fueling at 3-bars and have actual Ilco metal keys.

divemaster5734 said:

The whole problem with fuel level is the sensors will not be accurate if you don't take the level down after about 5 fills.
I noticed the reserve feature started tripping earlier and earlier, so I tested it.
I took a Rotopax can off another bike and stuck it in my top box when I was able to time the reserve to kick on when I was home.
When I first got the bike I measured around 340 miles before the reserve light went on.
Then it started kicking on around 300 miles.
Granted I started riding a lot more aggressively, but that was a big drop.
I took off and went for a ride with the spare gas and the reserve was showing 42 miles.
I didn't ride out the tank because I didn't have time but it stayed at 42 mile range for several miles before dropping to 41 mile range.
I rode a 20 mile loop but it still showed 35 miles.
I called the dealer's service dept the next day and was told the level sensor "recalibrates" itself and if never run low it will have errors indicating less gas than what is actually present.
They said the best practice is to run it partway down on reserve.
I've noticed about every 5 or 6 tanks the levels seem wonky.
That reserve flash and miles left feature is automatic on my bike.
Don't know if that's a setting, I got mine with 1500 miles on it in mint condition.

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It's possible some other factors (wrist, speed, traffic, coolant temperature, seasonal fuel blend, etc.) are affecting fuel mileage which impacts noted distance of 340 or 300 miles on the trip meter. When approximately 5 liters remains in the lower tank the last bar begins to blink and reserve starts counting distance/fuel amount remaining. Average and instant mpg during the first 7 bars on the fuel gauge is calculated from the vehicle speed sensor and rate of fuel pulses sent to the ECM. It updates every 15 seconds when in instant mode. The reserve system is fairly simple in operation and shouldn't lend itself to coming on earlier and earlier.

The thermistor location is fixed at a certain level in the lower tank (at apprx. 5 liters or 1.3 gallons remaining). If you started the bike with 1 bar blinking the distance remaining to empty and the fuel remaining will not be accurate as the system uses the average fuel consumption of the preceding uninterrupted 20 minutes of operation times fuel remaining when the bar begins to blink. The distance to empty is then recalculated every 15 seconds. The amount of fuel remaining is calculated by the fuel pulse signal sent to the ECM or the time it takes to burn 10 cc of fuel.

I tried to run my fuel tank down real low for the first time so I could take my tank off. I decided the weather was too hot so instead I decided to fill it up again. I was down to 2 bars and had a few short trips watching the gas gauge closely, but I concluded that it was so easy on gas, it wasn't going to 1 bar just yet. On my way to get fuel, I finally saw 1 bar and not long after, I saw a flashing 1 bar. I never saw that before so I stopped to get fuel immediately instead of getting gas at my usual stop, Costco.
It seemed like the 1 bar fuel level wasn't a significant amount, before it went to flashing? Interesting how our gauges read and act a little differently.

In my experience the one bar before flashing, contains about one gallon of gas. I have routinely travelled 45 miles in that last bar, before getting to the flashing bar. However this was on the interstate at a constant speed. Driving habits and condition dictate mpg.

The question I often think about is that is there any fuel left in the lower tank when the engine runs dry or is the lower tank completely dry.

etalors said:

In my experience the one bar before flashing, contains about one gallon of gas. I have routinely travelled 45 miles in that last bar

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Same here, the last solid bar lasts about an hour for me too.
Then the last blinking bar states I have 80 Km's or 50 miles left of driving.
If you shut your bike off in the blinking state, and start it back up, you won't have an accurate reading of Km's/ miles left.
Fill up ASAP as the fuel pump is cooled by fuel as previously mentioned on here.