Incorrect Fuel Amount Used

[maerlim]

I reset my trip calculators every time I fill up at the gas station. In doing so, I've noticed that the trip calculator is not reporting the correct amount of fuel that I used. It's usually around an entire gallon on the low side, when compared to how much gas I put into the car at the station.

Has anybody else noticed this problem? Is there an error in how it calculates fuel used, like it doesn't take idle time into account or something? Does anybody know how it measures fuel used (is there a physical meter in the tank, or does it "guess" based on some usage parameters)? And lastly, is this fuel usage used in calculating the MPG in the Fuel Economy screen?

 

[kert0307]

It guesses based on the commands sent to the fuel injectors. Yes, it uses that data in the fuel economy screen and it uses that mpg along with the signal from your fuel tank gauge to calculate "miles to empty"

 

[maerlim]

It guesses based on the commands sent to the fuel injectors. Yes, it uses that data in the fuel economy screen and it uses that mpg along with the signal from your fuel tank gauge to calculate "miles to empty"

So my "miles to empty" thinks I've used an entire gallon less of fuel than I really have? This could be a problem.

 

[joecrna]

But it is common to virtually every vehicle on the road. Every Toyota I've measured is hopelessly optimistic, usually off by 15-20%. Even the Prius. Only way to measure true mileage is add up every drop of gas added to the car over many (3000) miles and then divide it into the distance covered. It will still be off some, odometers are usually off some too unless they have been calibrated often.

Strangly enough, they are usually fairly acurate about "miles to empty" as the tank nears empty. Perhaps the fuel gauge measures what is in the tank and they then combine this with the average MPG. Actually some even take into account average MPG and recent MPG.

 

[kert0307]

So my "miles to empty" thinks I've used an entire gallon less of fuel than I really have? This could be a problem.

No, it uses the calculated miles per gallon. And applies it to the calculated gallons in the tank based off of the fuel level gauge.

 

[HBDY865]

When it says you have 0 miles to go, you still have about 2 gallons left. Look in the owners manual and see how big the tank is, fill it up. Then compare what the message center says and compare it to how much gas you put in next time you fill up.

 

[peterk9]

But it is common to virtually every vehicle on the road. Every Toyota I've measured is hopelessly optimistic, usually off by 15-20%. Even the Prius. Only way to measure true mileage is add up every drop of gas added to the car over many (3000) miles and then divide it into the distance covered. It will still be off some, odometers are usually off some too unless they have been calibrated often.

Strangly enough, they are usually fairly acurate about "miles to empty" as the tank nears empty. Perhaps the fuel gauge measures what is in the tank and they then combine this with the average MPG. Actually some even take into account average MPG and recent MPG.

I think the Miles to Empty (MTE) number that show after a fill up is based on the previous average MPG figure but the actual MTE is based on curent/recent figures. I would have to look at it again but I think a number of months ago I had that screen displayed and it seems that the MTE dropped at a slower rate when I was on the highway compared to non highway driving. The MTE rate was being compared to the odometer reading.
It would make sense to me that the MTE figures after a fill up would be based on your recent MPG's since your driving style and commuting (hwy/city) may not always be the same.

Peter

 

[peterk9]

When it says you have 0 miles to go, you still have about 2 gallons left. Look in the owners manual and see how big the tank is, fill it up. Then compare what the message center says and compare it to how much gas you put in next time you fill up.

18.6 gallons or 70.4 litres.

 

[harlenm]

My gallons used is within .05 gallons when I fill up at the pump.

 

[cmdrivan]

I'm still wondering about this. I have bought gas 11 times, and I am filling up with about 8% more gallons of gas than what the advanced trip computer shows I have used up. So the MPG on the trip computer reports higher numbers than why I calculate by hand.

I mentioned this in a previous post. Someone there suggested it may be due to a difference between winter blend gasoline and non-winter (??) blend. (I know that the refineries change up how they make gas over the winter, but I don't know if they change up for each season.)

This person also suggested it could be due to gas station measurements (in other words...ripping people off). In the 11 times I filled up, I've been to 4 or 5 gas stations with about the same 8% difference.

Now, I'm thinking that during remote start, the computer doesn't include that idle time in its gas usage calculation. I use remote start frequently and let it run for about 5 or so minutes before I get in and start it normally. I'll test this theory out next month when the morning weather is better.

_______________________________________________________________________________
2012 Ford Explorer Limited 4WD | 302A | Moonroof | Crossbars | Tow Package | Splash Guards
2007 Ford Focus SES ZX4

 

[vfral1]

Now, I'm thinking that during remote start, the computer doesn't include that idle time in its gas usage calculation. I use remote start frequently and let it run for about 5 or so minutes before I get in and start it normally. I'll test this theory out next month when the morning weather is better.

I think you've found the answer to your question. The Ford Engineers probably don't want everyone getting MPG's that are way off due to idling vehicles.

 

[dco43054]

So my "miles to empty" thinks I've used an entire gallon less of fuel than I really have? This could be a problem.

I view all of these things as estimates based on fuel flow, current average MPG, etc.

But they are just estimates.

When the gas gauge gets to 1/4 tank, fill it up, note how much fuel you've used and the mileage since last, and that will get you a much closer estimate.

 

[VinceL]

In my search for reliable fuel mileage data, I go to the same gas station every time, use the same pump every time, and always use the slowest notch on the handle to fill for me without topping off. I can only guess that it is working, but my mileage is very consistent in my weekly commute.

 

[Joe Dirt]

Why do I think of this clip when I read this thread?

 

[peterk9]

Strangly enough, they are usually fairly acurate about "miles to empty" as the tank nears empty. Perhaps the fuel gauge measures what is in the tank and they then combine this with the average MPG. Actually some even take into account average MPG and recent MPG.

As a follow up to my post above, the total Miles To Empty (MTE) reading after a fill up is base on your previous average MPG. I have confirmed that once you begin driving, the MTE figures are based on your current driving average. I drove through my subdivision and the the MTE number drop by 1 km after having driven only 0.7 km. When I got to the main road and drove at 80 kmph, the MTE number dropped by 1 km after having driven 1.4 km. At 100 kmph, the odometer and the MTE are pretty well at a 1 to 1 ratio.

Peter

 

[peterk9]

I view all of these things as estimates based on fuel flow, current average MPG, etc.

But they are just estimates.

When the gas gauge gets to 1/4 tank, fill it up, note how much fuel you've used and the mileage since last, and that will get you a much closer estimate.

Because of the posts here, I noted the figures when I filled up last night. The left screen showed I had used 41.7 litres (9.17 gal) or 11 U.S gallons. The pump clicked off after pumping 45.56 litres (10.02 gal) or 12.03U.S. gallons.
So as others have posted, I also put more gas in than I apparently took out.
I wonder if the so called 'emergency' amount comes into play here somewhere. :scratch:

Peter

 

[CulturalInfidel]

There's no fuel "flow" meter. As someone else pointed out, the engine control computer estimates fuel used based on commands it has generated for the injectors. It's close enough (except, perhaps, for those guys from "The Office".)
MTE uses input from the tank gauge and recent MPG estimates.

So: your cars computer has a certain acceptable margin of error, so does the tank gauge, and so does the pump at your local petrol station. Sometimes the errors are small and you'll get accurate results... sometimes the errors compound each other and you could easily be off by a gallon. (or two liters )

It's not a bug or a fault... just the margin-of-error as result of trying to give you some convenient information (MPG and MTE) using the available metrics, without incorporating much more expensive parts like flow-meters and ultra-accurate tank gauges.

 

[broken strut]

I filled up on Montreal and it said I had 630km to empty. When I filled up in Nova Scotia it said I had 500km to empty. WTF? Both times I filled it to the brim. 130km is a large difference. The next time I filled up it said 553km to empty. This is all highway driving at approx 120km/h. Reading says I'm getting 11.9 L/100km

 

[peterk9]

I filled up on Montreal and it said I had 630km to empty. When I filled up in Nova Scotia it said I had 500km to empty. WTF? Both times I filled it to the brim. 130km is a large difference. The next time I filled up it said 553km to empty. This is all highway driving at approx 120km/h. Reading says I'm getting 11.9 L/100km

What kind of driving did you do prior to filling up in Montreal? If your average km/100km was lower at that time (ie 10.9 L/100km) it would give you a higher km to empty than 11.9 would. Driving at 120 will not give you the same mileage as driving at 100 or even 110. The computer takes everything into account when giving you the kms to empty (starts, stops, hills, wind, etc.)
Not sure what you mean by filling it to the brim. The manual says to not let the pump click off more than 2 times. Perhaps you are lossing some to the overflow tube??

Peter

 

[Spengracin]

This a soar subject, at idle your mpg drops considerably, really? Last trip mine said I had 335 miles to empty, filled up today, it says 240. This system sucks.