[Aggie86]

Well, just finished burning out the first tank of gas that i puchased after using up the fuel provided by the dealer at delivery. I've been pretty aggressive in my driving (R/T) and the EVIC showed 15.5 mpg which I though was pretty good considering it was all in town mileage. The hand calculation however only came in at 10.5 mpg. :Wow1: Anyone else seeing that huge split and anyone else realizing mileage in that range?

 

[Thumper14]

Holy cow, a 5mpg difference?!?! How big is your tank and did they fill it up completely? I hand calculated on my old truck once just to check and was off a bit because I thought the tank was 2 gallons bigger than it actually was

 

[Blackhawk]

My experience with 3 vehicles is the computer is off 10% high. This truck is 9% high. If you check another 5 - 10 tanks you'll get a good idea of the EVIC accuracy.

 

[Hermes1]

That is a big difference, even considering for a first tank. Up until I reached approximately 7000 miles, my EVIC was about 3 mpg optimistic. Since 7K the EVIC is anywhere between .5 and 1 mpg optimistic.

 

[Monster5601]

Just about every model year forum has a discussion about the accuray of average MPG. Since I have first hand knowledge of how the calculations are done I will say the accuracy is right on, plus or minus the display digit count and number rounding in the calculations. Fuel consumption is the sum of the count and duration of the fuel injectors. To calculate the MPG the distance traveled and the fuel consumed yields an instant MPG which is used to average the overall MPG over time.

The error that you you see when hand calculating between fill-ups is introduced because the calculations have no knowledge of how much energy is in the gallon of gas you buy and deltas during filling up. Ethanol is blended with gasoline in varying amounts and ethanol contains less energy, the higher the ratio of ethanol, the less MPGs or the more fuel used.

I have found over the past year, my average MPG versus my hand calculation deltas occur during the time when the switch from/to summer/winter blends. If you know when that happens, reset your average MPG and the calculations will be more accurate with respect to time.

 

[Thumper14]

Just about every model year forum has a discussion about the accuray of average MPG. Since I have first hand knowledge of how the calculations are done I will say the accuracy is right on, plus or minus the display digit count and number rounding in the calculations. Fuel consumption is the sum of the count and duration of the fuel injectors. To calculate the MPG the distance traveled and the fuel consumed yields an instant MPG which is used to average the overall MPG over time.

The error that you you see when hand calculating between fill-ups is introduced because the calculations have no knowledge of how much energy is in the gallon of gas you buy and deltas during filling up. Ethanol is blended with gasoline in varying amounts and ethanol contains less energy, the higher the ratio of ethanol, the less MPGs or the more fuel used.

I have found over the past year, my average MPG versus my hand calculation deltas occur during the time when the switch from/to summer/winter blends. If you know when that happens, reset your average MPG and the calculations will be more accurate with respect to time.

Wow. This response wins this thread. :Wow1:

 

[rgardjr]

Here are my numbers over the first 4859 miles:

DATE Hand EVIC Difference
03/30/14 18.33 20.0 +1.67
04/18/14 16.81 17.8 +0.99
04/22/14 16.78 18.4 +1.62
04/27/14 13.17 13.4 +0.23
05/05/14 15.69 17.1 +1.41
05/13/14 17.67 19.3 +1.63
05/27/14 17.83 19.9 +2.07
06/03/14 17.51 19.2 +1.69
06/12/14 16.46 18.2 +1.74
06/19/14 15.90 17.7 +1.80

EVIC has been reset after every fill up. Doesn't appear to be getting any more accurate as we have returned to "summer blend" season.

 

[Jimbom]

Just about every model year forum has a discussion about the accuray of average MPG. Since I have first hand knowledge of how the calculations are done I will say the accuracy is right on, plus or minus the display digit count and number rounding in the calculations. Fuel consumption is the sum of the count and duration of the fuel injectors. To calculate the MPG the distance traveled and the fuel consumed yields an instant MPG which is used to average the overall MPG over time.

So there is no mechanical flow meter somewhere in the fuel line measuring the flow rate of fuel being consumed?

Jim

 

[Jimbom]

My first re-fill (250 miles driven) had a similar spread, but not quite as big. EVIC said ~15 mpg, actual was ~11 MPG. 2nd tank (350 miles driven) was much closer; EVIC said ~14 mpg, actual was ~13 mpg.

I must say, however, that the EVICs indicated range (@ 65 miles till empty) was spot on, assuming I have 32 gals usable. The low fuel warning came on with about 75 miles till empty.

Jim

 

[lsfdfire]

I have 3000 mi. On my 2014 Ram ED and my EVIC is right on with my hand calculation.

 

[Gantman]

My hand to EVIC calculations are generally a one mile per gallon difference everytime. That's real good in my book.

 

[Red-Stripe]

Just about every model year forum has a discussion about the accuray of average MPG. Since I have first hand knowledge of how the calculations are done I will say the accuracy is right on, plus or minus the display digit count and number rounding in the calculations. Fuel consumption is the sum of the count and duration of the fuel injectors. To calculate the MPG the distance traveled and the fuel consumed yields an instant MPG which is used to average the overall MPG over time.

The error that you you see when hand calculating between fill-ups is introduced because the calculations have no knowledge of how much energy is in the gallon of gas you buy and deltas during filling up. Ethanol is blended with gasoline in varying amounts and ethanol contains less energy, the higher the ratio of ethanol, the less MPGs or the more fuel used.

I have found over the past year, my average MPG versus my hand calculation deltas occur during the time when the switch from/to summer/winter blends. If you know when that happens, reset your average MPG and the calculations will be more accurate with respect to time.

That's messed up.
There's no error introduced with hand calculations because of fuel BTU's
MPG= miles per gallon. distance measurement/ volume measurement.

If you meant to say the computer messes it up, then there again, its injector volume, duration and frequency, giving a total fuel volume calculation again. distance per volume again.

 

[Jimbom]

That's messed up.
There's no error introduced with hand calculations because of fuel BTU's
MPG= miles per gallon. distance measurement/ volume measurement.

If you meant to say the computer messes it up, then there again, its injector volume, duration and frequency, giving a total fuel volume calculation again. distance per volume again.

I hope he's not trying to pin the difference we see on some error in our hand calculations. As you said, our calcs have nothing to do with the energy content of the fuel. If I read his post right, they are estimating a fuel flow without actually measuring it with a flow meter. However, his explanation didn't really make clear to me how the energy content of the fuel affected that either.

The only error in our calculations is the slight variation in how full we get the tank each time. The emptier the tank before the fill-up (i.e. the more gals used in our calculation), the less significant that error is. Averaging a series of fill-ups drives that error close to zero.

Jim

 

[Bushmaster]

Mine is pretty accurate, between hand calculations and EVIC is only off maybe 1 to 1.5 litres, I can live with that.:smileup:

 

[Monster5601]

EVIC has been reset after every fill up.

If you reset the EVIC after each fill-up, you will never get your average MPG over time. Quit resetting it.

So there is no mechanical flow meter somewhere in the fuel line measuring the flow rate of fuel being consumed?
Jim

It isn't needed with fuel injection. Knowing the fuel line pressure, the injector flow rate, the duration the injector is open, plus the count of injector openings equals the amount of fuel used.

My hand to EVIC calculations are generally a one mile per gallon difference everytime. That's real good in my book.

Excellent, variations between average and hand calculations assuming the same energy level of the fuel should be with in 5% or better.

That's messed up.
There's no error introduced with hand calculations because of fuel BTU's
MPG= miles per gallon. distance measurement/ volume measurement.

Correct, but that isn't what I said, the delta is seen because when you fill up there is no way to know how close to full you are with respect to the last fill up. The temperature of the gas you pump also controls the volume since gas expands as temperatures rise. Granted these are small amounts but the sum of all factors does affect the result.

A trend lately has been to display the average MPG over the last 50 miles driven in an attempt to make more accurate the average displayed to reduce complaints.

 

[jdw174]

My first fill-up the EVIC showed 16.2, calculator showed 14. That's the way it's remained...with the EVIC being about 2mpg high. I just returned from an 1800 mile trip where the EVIC showed 26mpg at one fillup, while the calculator showed 22. Apparently the better you do, the bigger the difference....at least on mine.

 

[TMorgan]

I've never reset the average mpg on my Evic since new on my 14 ED and believe it to be pretty accurate,maybe even a little low.I do reset the trip meter "A" on every fill up and it's always about 1 mpg low compared to my hand calcs.I fill at the same station most every time.The speedo is spot on too.I now have 2700 miles on my truck(5 fill ups) and love it.Average mpg since new is always between 24-26 on the Evic depending on trips.This is with 3.92 gears,very little highway and mixed driving with about 25% short trips under 6 miles.:smileup:

 

[rgardjr]

If you reset the EVIC after each fill-up, you will never get your average MPG over time. Quit resetting it.

I reset one trip meter and have left the other one alone. That being said I find it laughable that you say I will never get my average MPG over time. I know it because I hand calculate. When I want to figure out the actual range that I have left on my current tank I look at the trip EVIC mpg and subtract 1.75 mpg it to use in my calculations-this will be much closer than what the EVIC reports. Pretty ridiculous in this day an age that a 5% margin of error could be considered "excellent".

 

[Blackhawk]

This may be a defect in my EVIC, but after a long trip the "B" MPG's were exactly the same as the "A" reading. I had never reset the "B" readings hoping to her an avg of MPG's for the trip. The "A" reading was reset at each fill up. "B" had the total miles, hours etc. but not the correct MPG's. No fill up on the trip was ever as low as the final fill up. Apparently every time I reset "A" it also reset "B" mpg's.

 

[GoneWithOutA]

This may be a defect in my EVIC, but after a long trip the "B" MPG's were exactly the same as the "A" reading. I had never reset the "B" readings hoping to her an avg of MPG's for the trip. The "A" reading was reset at each fill up. "B" had the total miles, hours etc. but not the correct MPG's. No fill up on the trip was ever as low as the final fill up. Apparently every time I reset "A" it also reset "B" mpg's.

I have noticed the same on mine. I reset Trip Meter A daily, Trip Meter B has never been reset. The mpg in Trip B does not seem to indicate my usage since new. I log all my fuel and distances for work so my spreadsheet includes calculations for average consumption since almost new (disregard the fuel and driving after delivery)

That being said my last couple tanks of gas have been less than 1 mpg different from the EVIC. Perhaps a function of summer blends and location use.