Dash calculated fuel consumption average vs hand calculated average

[gsbrockman]

I'm right and you are an idiot....means I am right and you are an idiot.

Reallllllllll classssssss.

 

[garrettg84]

All I can add is "assume" = "***" out of "u" and "me"....

You called me an *** using ridiculous para-quote from Oscar Wilde. I'm the one with a class problem though.

“But when assumptions are sometimes true. Then you're the ***, not me. ”
~ Bryan Yeo

 

[TRAMPLINEMAN]

My usual tank of fuel is roughly 80/20, city/freeway miles, with a short freeway commute. Summer months the evic is usually in the 15.6 to 15.8 mpg range, during the so cal winters, the evic shows in the 14.4 to 14.8 range. My hand calcs are pretty much 1 mpg less........again..... Because of some serious health issues (the wife) I have yet to do any towing of any distance or even a full tank of freeway miles. I'm quite curious of my towing mileage and empty trip mileage but that's going to have to wait a bit.....

Sam

My usual tank is 80/20 with 80 being freeway miles. This winter the dash average has ranged from 14 to 17.5. I bought the truck around September so I don't know what the summer mileage will bring.

 

[TRAMPLINEMAN]

COurse if you want to, you could always get one of these…I have used it for several years now on my farm tank with no problems.

https://excel-equipment.com/farm/meters/fuel-meters/fill-rite-in-line-digital-meter.html

We have those on all our work trucks for tax reasons. Every winter, every one of them freezes up and ruins your day.

 

[Trowel2013]

The fact of the matter is, whatever algorithm Ram engineers are using for the EVIC is flawed. Nobody gives a rats *** about a arbitrary number of miles prediction. That type of calculations is completely useless and inaccurate in the real world, period. The technology is there and capable of giving real world usable information on an instantaneous basis, why Ram doesn't utilize it is beyond me and apparently a lot of other people. Regular combustion engine prop planes have had this technology for decades and are very accurate.

If your one of those that feels it is accurate and it gives you a warm and cozy feeling, then so be it. Just don't expect the rest of us to feel the same way when we expect it to work in a practical and logical way.

 

[garrettg84]

The fact of the matter is, whatever algorithm Ram engineers are using for the EVIC is flawed. Nobody gives a rats *** about a arbitrary number of miles prediction. That type of calculations is completely useless and inaccurate in the real world, period. The technology is there and capable of giving real world usable information on an instantaneous basis, why Ram doesn't utilize it is beyond me and apparently a lot of other people. Regular combustion engine prop planes have had this technology for decades and are very accurate.

If your one of those that feels it is accurate and it gives you a warm and cozy feeling, then so be it. Just don't expect the rest of us to feel the same way when we expect it to work in a practical and logical way.

If you were given a hammer and decided to use it as a screwdriver, would you be angry at the hammer manufacturer for not making it work better as a screw driver?

The MPG tool is evidently there to give you feedback on the recent MPG calculations. It is actually accurate for this. Fill up your tank. Reset your MPG calc. Drive for 30 miles. Refill. Hand calculate. I'm betting it will be spot on. Based on the recent driving, the EVIC makes a calculation on how far you'll be able to travel with your relatively current MPG calculation and the fuel left in the tank. Come up to a long steep grade? Things start changing depending on if you are going up or down.

It is nothing about warm and cozy. I'm just not angry at the tool manufacturer for making a tool that doesn't do the job it wasn't designed to do. I'm simply stating how it works.

Argue all you want. Cry about it. Enjoy your warm cozies.

On a side note, regular engine prop planes don't regularly accelerate, decelerate, stop at traffic lights, idle in the air, deal with greatly varying terrain, or stop for school busses. Ask the guy who drives stunt planes with greatly varying engine RPMs how accurate those fuel left gauges are for his maneuvers (hint, they aren't). Predictions over a smoother course are MUCH easier. I don't know though, maybe RAM corp is God and they magically know the traffic and terrain ahead of you and can tell you when the next hill will show up or the next school bus stops all traffic. Maybe your expectations are just obscenely ridiculous.

 

[Hoefler]

I have a 2014 Laramie, I can go to the "A" & "B" trip and reset the mileage AND the MPG. It will calculate from the last reset. If you go to the economy screen, it will show what is happening "NOW" and the most recent. You can also reset the economy screen as well. All 3 can and will read differently, depending on when it was last reset. I use trip "A" for current tank fill mileage and MPG. I use trip "B" for the DEF consumption, as well the fuel economy for that period of DEF consumption. The economy lets me know what my foot is doing to the fuel economy right now.

 

[gsbrockman]

My dash calculated is actually pretty good. The only problem is that it is averaging over a shorter timespan than my tank of gas.

I think the mystery is solved :-laf apparently EVIC's utilized in CTD's are most accurate when the operator runs some grade of unleaded versus #2 diesel fuel.

 

[garrettg84]

I have a 2014 Laramie, I can go to the "A" & "B" trip and reset the mileage AND the MPG. It will calculate from the last reset. If you go to the economy screen, it will show what is happening "NOW" and the most recent. You can also reset the economy screen as well. All 3 can and will read differently, depending on when it was last reset. I use trip "A" for current tank fill mileage and MPG. I use trip "B" for the DEF consumption, as well the fuel economy for that period of DEF consumption. The economy lets me know what my foot is doing to the fuel economy right now.

You see that word average next to the ones over those different trips? It wouldn't need to say average if it was total miles over fuel consumed. It could simply say Miles Per Gallon. Average, from a mathematical/statistical point of view (the point of view engineers have) should make you wary of weighted averages and other such details. The reason they say average is because they are averaging over some time period (hint, it isn't since your reset unless you simply haven't filled the time period it is averaging over). Clearly I am getting nowhere showing you folks the math and why, regardless of what you want to believe, a short trip cannot affect your average if there are as many data points as you are claiming. It is just not mathematically possible. No way, no how.

 

[RustyJC]

I'm guessing that the EVIC programmers weren't directing the readout to us engineers, but merely used the word "average" to differentiate the readout from "instantaneous". I haven't tried to crack the code or made this a priority in my life, but my "average" fuel economy seems to be miles traveled divided by fuel consumed since last reset. The key variable is how the "fuel consumed" factor is derived - it seems to come from cumulative fuel flow as measured by the ECM (probably from a complex map that extrapolates instantaneous fuel flow as a function of engine RPM, accelerator pedal position, MAP, IAT and other inputs) as opposed to inaccurate tank level readings.

On my stock truck, the EVIC readout is generally within 0.5 MPG of my hand calculations, and even hand calculations for each fill-up are questionable as it's almost impossible to fill the fuel tank to precisely the same level every time.

Rusty

 

[Trowel2013]

If you were given a hammer and decided to use it as a screwdriver, would you be angry at the hammer manufacturer for not making it work better as a screw driver?

The MPG tool is evidently there to give you feedback on the recent MPG calculations. It is actually accurate for this. Fill up your tank. Reset your MPG calc. Drive for 30 miles. Refill. Hand calculate. I'm betting it will be spot on. Based on the recent driving, the EVIC makes a calculation on how far you'll be able to travel with your relatively current MPG calculation and the fuel left in the tank. Come up to a long steep grade? Things start changing depending on if you are going up or down.

It is nothing about warm and cozy. I'm just not angry at the tool manufacturer for making a tool that doesn't do the job it wasn't designed to do. I'm simply stating how it works.

Argue all you want. Cry about it. Enjoy your warm cozies.

On a side note, regular engine prop planes don't regularly accelerate, decelerate, stop at traffic lights, idle in the air, deal with greatly varying terrain, or stop for school busses. Ask the guy who drives stunt planes with greatly varying engine RPMs how accurate those fuel left gauges are for his maneuvers (hint, they aren't). Predictions over a smoother course are MUCH easier. I don't know though, maybe RAM corp is God and they magically know the traffic and terrain ahead of you and can tell you when the next hill will show up or the next school bus stops all traffic. Maybe your expectations are just obscenely ridiculous.

First of all, the hammer screw driver anology has nothing to do with this and is ridiculous. Secondly, my comments weren't directed at any one person (ie. you). Third, I don't fly, but know several people that do and there is quite a bit of variance of throttle input throughout the flight between elevation changes, wind speeds, air temperature, etc.. From my understanding, from talking to these aviators, the systems in their planes at least, use vary simple math. Time/fuel consumed updated continuously. Maybe stunt pilots systems are different, IDK and to be honest IDC.

If Ram is indeed using a algorithm like you discribed, what good is that to the average driver? I don't drive 30-50 miles and then fuel up. My EVIC has never been lower than HC. It doesn't matter if I drive a bunch of city, bunch of HWY, mixture of both. It doesn't matter if I drive empty for the majority of the tank and tow heavy for the last 75 miles of the tank and fill up then. It doesn't matter whether I tow heavy for the first 150 miles of the tank and drive all HWY for the rest of the tank. It's never constantly off. One time it might be .5 of a MPG off. The next it could be 3.2 of a MPG off. In the little over a year I have owned my truck I check every tank. I have yet to figure out a pattern. Now, does it bother me enough for me to dislike my truck and want to get rid of it? Hell no. I love my truck. One of the reasons I track it is it's trivial and I'm trying figure a pattern (ie. if I drive like this it will be x off, if I do this and this it will be y off).

On a side note, there is no need to bring ones mathematical or statistical abilities into question. I fully understand the math involved, so just don't. There is no need for trying to belittle are name call people here, we're all supposed to be adults.

 

[DJAustin]

My 2014 is constantly 2miles off, reading high.

 

[TRAMPLINEMAN]

I have a 2014 Laramie

Some guys just have too much money!!

 

[S.Morris]

Not real relevent but only as comparison:

We have a new 14 Jetta TDI. It has 2 running fuel/use/mpg /instant and average mpg. One trip meter can be set for length of trip or even distance between vehicle servicing. It will give a avg readout and an instant readout.
It has a second trip meter that does the same BUT it resets itself everytime the car is keyoff for more than 1 1/2hrs. Both of these over long or short term are very accurate when compared to hand calculated(only 1.-.3 off. Also the fuel guage is very accurate as is the distance to empty.

If the system they use can be this accurate then maybe Ram engineers need some lessons.

 

[Bob V]

Rusty, I think you are dead on. The only way I see the trucks computer can get fuel usage is using fuel pressure and injector open time to CALCULATE the amount of fuel used. The fuel is not measured so it is more Theory the actual amount. Also agree that hand calculations a can be way off also, lots of variables. I feel that a minimum 3 tank average is needed to get a true number for hand calculations. Any modifications done to change the output of the engine can have an effect on the computers calculations of fuel used and cause the readout to be off. My 2005 with oversized injectors read out was about 20% high. My 2011 with a Smarty is much closer and seems to change depending on what level I run it on.

 

[MGutierrez]

Gas Cubby

I use an app on iPhone called Gas Cubby that is very simple to use that you can keep track of everything you ever do to your vehicles. It even has info on all your averages such as,price per gallon paid, mileage, etc. It even displays info on a line graph if you want. I'm not sure how many vehicles you can keep track of but I have four on it. It will even remind you when it's time for service. I had an app on my Windows 7 Phone before I got my iPhone but it wasn't Gas Cubby. It also was easy to use I just don't remember what it was called but I'm sure all the smart phone platforms carry good apps for this purpose.

 

[DHuffman]

Over 10,500 miles so far mine is off by 8.6%, or 1.45 mpg. It is pretty consistent. I track every fill up, and I use the same station and pump 90% of the time.

 

[zb39]

I never knew people cared so much about mpg. Not a big deal though. I have never HC my mpg for this truck. I look at the EVIC once in awhile, don't really care what it says. I didn't buy it for MPG. It gets what it gets. I do really love the truck though. I think I get about 10 with the camper and 14 with out. This is based on the EVIC. Love the truck and the power. This is my 4th Dodge and the best for power.

 

[gsbrockman]

I never knew people cared so much about mpg. Not a big deal though. I have never HC my mpg for this truck. I look at the EVIC once in awhile, don't really care what it says. I didn't buy it for MPG. It gets what it gets. I do really love the truck though. I think I get about 10 with the camper and 14 with out. This is based on the EVIC. Love the truck and the power. This is my 4th Dodge and the best for power.

For those of us that use our trucks to put bread and butter on the table....it is "a big deal".

 

[jkern]

I have read with interest on this thread and with all the math and opinions that have been thrown around, it appears that there is one key factor that has only been "assumed" in all the calculations...Tire Size. The EVIC's are calibrated with the OEM stock tire size, if an owner puts a different tire size on the truck then all bets are off on a reasonably accurate calculation. A stock 265/70/17 tire has a height of 31.6" and a rolling circumference of 99.2 inches, while a 285/70/17 has a height of 32.7 inches and a circumference of 102.7 inches. This is about a 3.35 percent change, which at 14MPG is a difference of 0.4mpg. So with all the math and discussion, we have to assume that we all are running stock tires, OR everyone has calculated for the difference in tire size from stock.

Secondly...I have no proof, but i had been recently told by a few different people in the auto industry that most fuel consumption calculations are based on load, RPM and a few other factors; there is no flow meter, (in the aviation industry there are flow meters that may or may not be installed in planes.) Along these lines, i am pretty sure the EVIC uses a rolling number of gallons on which to base its calculation or from a reset. I recently had a GM product and was talking with a GM Engine Control Engineer and they used a rolling 30 gallon calculation, meaning that the MPG reported on the dash was only based on the last 30 gallons of fuel used. This would explain the reason that if you never reset the EVIC (for 3000 miles) that the MPG reported on the dash would still change on short 6 mile trips.

Lastly...on my 2011 my EVIC reported mileage is interesting versus the hand calculated method: at 14.5 - 15MPG range the EVIC and hand calculated are right on, but less than 14mpg, the EVIC reads lower than hand calc by about 0.7mpg and over 15 MPG it is about 0.4mpg over the hand calc. So i would assume that it is mostly accurate around the 14.5-15mpg range, which coincidentally is generally what these truck run...depending on load, terrain, driver, etc. I generally get 14.8-16mpg as a daily driver with mixed driving and about 10.5-12 towing 7000 pounds.