Why the top fuel level bar lasts so long

[HerrDeacon]

Thanks for posting this CTScott. I just recently bought a Yaris and I'm still on my first tank, but I did wonder why the top bar lasted so long compared to the others...well now I know, thanks.

[Yarrris-Wench]

Originally Posted by ddongbap

+1. CTScot for president of something.

+2!! This is quite interesting!

[why?]

don't run this tank dry. If the car stops because of no fuel, you will not be able to get it started again at all, and will have to go get gas. i did it once, trying to see how far I could go on a tank of gas. I've never had a car that just simply refused to start like the Yaris did.

[Kal-El]

Originally Posted by why?

don't run this tank dry. If the car stops because of no fuel, you will not be able to get it started again at all, and will have to go get gas. i did it once, trying to see how far I could go on a tank of gas. I've never had a car that just simply refused to start like the Yaris did.

Am I reading this right? You're wondering why the Yaris won't restart after you stall out by running it dry?

Hint: gas powered cars do not run without gas.

[CTScott]

Originally Posted by Kal-El

Am I reading this right? You're wondering why the Yaris won't restart after you stall out by running it dry?

Hint: gas powered cars do not run without gas.

I know what he means. On some cars, when they run out, you can restart them, and drive them gently (to keep the last bit of fuel as stationary as possible) a bit until they die again. The way the Yaris' fuel system works you can't - Once it quits, it's done.

[tk-421]

@CTScott: Is there a way to measure (in a more precise manner) how much fuel is left in the tank by using an OBD module?

[CTScott]

Originally Posted by tk-421

@CTScott: Is there a way to measure (in a more precise manner) how much fuel is left in the tank by using an OBD module?

Not really. There isn't an OBD command for fuel level. If we knew the secret Toyota handshake, I could poll the cluster for the fuel level, but that would be the same latent data that the fuel gauge shows.

The problem with doing it by fuel flow is that it is one way. Unless you could also read the flow rate into the tank, you'd still be working down from an approximation.

[CTScott]

Originally Posted by PK198105

why would you need a two way? if we would be able to read the fuel flow, then each time you would fuel up you would input the amount into the ucontroller and then just use the fuel flow to calculate the instantaneous fuel level. you could program the ucontroller to always take under consideration whatever is left in the tank and then add this amount to the amount you put in at the gas station. not sure if i'm explaining it clearly

I know what you mean. Actually, the fuel flow rate is calculated from the MAF flow rate (there's not a standard PID for fuel flow), so even that is an approximation.

[127.0.0.1]

Originally Posted by CTScott

I know what he means. On some cars, when they run out, you can restart them, and drive them gently (to keep the last bit of fuel as stationary as possible) a bit until they die again. The way the Yaris' fuel system works you can't - Once it quits, it's done.

it will sputter a bit then run good, alerting you that only minutes
remain and you are walking.....


my 4runner does that with <1/2 gallon left


it dies. you stop, wait, start again. in 3 miles it dies again.

start back up, you have 2 miles left, at most

[MadMax]

My favorite Mythbusters explosion!

Mythbusters - Compact Compact Rocket Sled

Thank God it wasn't a Yaris at the end!

Cheers! M2

[Idahotom]

100 % useable? great! I don't much care how long the first bar or two takes, its the apparent speed up of the flashing last bar, usually when I'm some distance away from a station, that always gets me by surprise. My other Toyota is exactly the same in that respect, it seems to go from 3/4 empty to empty real quick, I've learned to ignore it, to some extant, and have never run out totally. Knowing what I know now, I'll probably push it even more! 10.48 gallons at my last fillup, just right.

[OTA'sTOY]

commom sense will tell you if you close to empty
"only got 1 bar left" ....get gas....
pay now or pay later

[nookandcrannycar]

Originally Posted by CTScott

There have been quite a few threads in the past that discussed this, but here's a Mythbusters style analysis of it (fortunately, minus the large explosion at the end):

Today I am working on the range until empty and fuel level in gallons (or liters) features for my YarGauge project. I drained Crashy's fuel tank and then added 1 gallon (precisely measured with a one gallon laboratory flask) at a time while recording the data values from the analog to digital converter, which I have connected to the fuel level input to the instrument cluster.

I plotted a graph to see how linear (or not) the fuel sender value is in regards to the volume in the tank. From bone dry to the top of the filler pipe, I was able to put in 12.8 gallons. The ADC value stops changing at just over 11 gallons.

So, you can put just shy of two gallons more into the tank than the fuel gauge can measure.

Attachment 31330

Interesting. This is the first time I've seen or read this post. This jives with what I experienced after running out of gas while pulling into a gas station to get gas. I filled it (as I always do when filling a tank) to the point where I can barely see the gas and the pump registered 12.777 gallons. It stands to reason that the remaining .023 gallons would = any difference between my level and the 'top of the filler pipe' CTScott describes and the small amount in the bottom of the tank that CTScott describes in a later post to this thread.

[nookandcrannycar]

Originally Posted by why?

don't run this tank dry. If the car stops because of no fuel, you will not be able to get it started again at all, and will have to go get gas. i did it once, trying to see how far I could go on a tank of gas. I've never had a car that just simply refused to start like the Yaris did.

I have a AAA Plus membership and the Yaris is so reliable that since purchasing it the only tangible value I've gotten out of the membership is when I've run out of gas. The intangible value of the peace of mind the membership confers is, to me, worth the cost. For some people, re location, a AAA membership would be a waste of money. I used to live part time in Mammoth Lakes, California. I didn't need a car to get around, but I had my car there anyway. I locked my key in my car. I called AAA and they couldn't help me. The maximum range from a contract station at that time (on my membership) was 50 miles and no contract station existed within 50 miles of Mammoth Lakes. I had to wait until my girlfriend could bring me another key on her next visit from Orange County.

[DonM]

I don't understand why anyone would want to let their fuel level drop to less than a 1/4 of a tank as I was always under the impression that any crud that may have been accumulated from using "dirty" gas is usually sitting at the bottom of the tank.

I know of 2 people who ran out of gas and a short time later - their fuel pumps died (one of them was a Chev Montana van and the cost to repair the fuel pump was $750.00).

[rningonfumes]

I almost always run it down leaving just about 1 gallon left. It helps me to keep track of my mileage more efficiently (by glancing at the trip meter). As soon as the last bar blinks, I use the trip meter to confirm how much gas I have left and plan the gas run accordingly.

[why?]

Originally Posted by nookandcrannycar

I have a AAA Plus membership and the Yaris is so reliable that since purchasing it the only tangible value I've gotten out of the membership is when I've run out of gas. The intangible value of the peace of mind the membership confers is, to me, worth the cost. For some people, re location, a AAA membership would be a waste of money. I used to live part time in Mammoth Lakes, California. I didn't need a car to get around, but I had my car there anyway. I locked my key in my car. I called AAA and they couldn't help me. The maximum range from a contract station at that time (on my membership) was 50 miles and no contract station existed within 50 miles of Mammoth Lakes. I had to wait until my girlfriend could bring me another key on her next visit from Orange County.

So true. When I was working in florida I lost so many keys I had to call for locksmiths far too many times. At this point I always walk around with at least 3 keys on me. I wouldn't ever get in a car without a valid AAA membership.

Originally Posted by DonM

I don't understand why anyone would want to let their fuel level drop to less than a 1/4 of a tank as I was always under the impression that any crud that may have been accumulated from using "dirty" gas is usually sitting at the bottom of the tank.

I know of 2 people who ran out of gas and a short time later - their fuel pumps died (one of them was a Chev Montana van and the cost to repair the fuel pump was $750.00).

Never using bad gas is the easy way to fix this. Everyone knows what the good gas is in their area, you should keep to it. Where I live, the two best gasses actually help to increase gas mileage as well.

Not to mention if you run the tank lower, none of that crud ever has the chance of building up since it is all used.

[DebbyM46227]

I never let my car run out of gas, but I have the same thing as AAA included in my car insurance. It covers towing, flat tire changes, locksmith, battery jump-starts, and fuel/fluid delivery for $2.00 addl. every 6 months. So far, haven't had to use it with my Yaris for anything (knock on wood) but when I had the Cavalier I took advantage of it 3 times for flat tire changes.