Took the 6.4 on a road trip

[sandawilliams]

I awta check my wifes denal just for ***** and giggles. Judging by the graph, you must have a cummins lol.

Isnt it funny how the computer magically reads better mpg instead of worse?

That's why I call it a 'feel good' reading. The evic makes you fill good about your mileage then you hand calculate and reality sets in.

 

[SouthTexan]

I awta check my wifes denal just for ***** and giggles. Judging by the graph, you must have a cummins lol.

Isnt it funny how the computer magically reads better mpg instead of worse?

Yeah, both vehicles are deleted diesels. I probably could get better out of the truck, but the aggressive 35" tires along with the my unwillingness to go below 75 mph takes its toll on my mpgs. Since I bought the car, I hardly drive my truck except for weekends so when I do get to drive it I tend to care less about what kind of mileage it gets because I am enjoying it too much.

 

[68PowerWagon]

Not always. I've hand calculated my mileage and it's always pretty close to the eviic...usually .5-1 mpg less by hand....but my truck is all stock and I run 70 psi in all tires so I think that's part of it....but who knows? Maybe i just got lucky with a semi accurate evic? Lol!

Yeah that's about all mine is off by... 1/2 to 1mpg. I have gotten up to 20.2 (evic) on some back highways averaging 60mph. Also have gotten 16mpg pulling a 4,200 pound boat & gear. Seems like I get my best mpg when I am heading east. And in the Midwest there always seems to be at least a little breeze coming out of the northwest.

 

[runamuck]

seems like the car computer would be pretty accurate as it would know the exact amount of fuel passed by the injectors and would know the total number of tire rotations. the only variables would be tire inflation would impact the tire diameter slightly. idle time would impact the mpg but not make the number incorrect. just thinking out loud

 

[SouthTexan]

The computer does not know the exact amount of fuel being added. It just adds fuel based on how much air is being added on a gaser to stay around a 14.7:1 ratio.

 

[olyelr]

seems like the car computer would be pretty accurate as it would know the exact amount of fuel passed by the injectors and would know the total number of tire rotations. the only variables would be tire inflation would impact the tire diameter slightly. idle time would impact the mpg but not make the number incorrect. just thinking out loud

^^^^ this

The evic should be more accurate than hand calculating in my opinion. Its just two simple pieces of data that it needs to know; fuel used and miles traveled. How hard is it for them to have the computer accurately read those two?

An error that could be a factor with hand calculating is not filling the tank to the same exact level each time. While not a real big difference, I suppose it could easily be a half gallon or so different each time.

 

[olyelr]

The computer does not know the exact amount of fuel being added. It just adds fuel based on how much air is being added on a gaser to stay around a 14.7:1 ratio.

So they can figure out how much air is used, then they make some crazy calculation to get how much fuel is used? Wtf. Why not just read how much fuel is being sucked out of the tank and be done with it.

 

[SouthTexan]

So they can figure out how much air is used, then they make some crazy calculation to get how much fuel is used? Wtf. Why not just read how much fuel is being sucked out of the tank and be done with it.

Because you have many variables like fuel/air density due to temperature, pressure, and so on. The fuel is pressured up to the injectors and then the injector is told when and how long to inject fuel depending on what the fuel map in the ECM is telling it to based on air mass, rpm, throttle position, and so on.

Not only that, but to add a device to measure fuel rate at each injector would add cost with no real added benefit when a simple (and lest costlier) computer algorithm will do even though it is not dead nuts accurate.

 

[sandawilliams]

I am on my 6th FCA product with evic. Every one of them were off at least 1-2 mpg from actual mileage. They always read higher. My Mustang is just the opposite. It always reads lower than actual.

 

[SouthTexan]

I will add that the computers fuel algorithm is only as good as the sensors giving it the data. Not all sensors are dead nuts accurate or read exactly the same. You can have two sensors side by side, and both may be slightly off depending on which side of the bell curve they are on. Contamination on a sensor or slight leaks in the intake/exhaust may also play a role.

 

[olyelr]

Because you have many variables like fuel/air density due to temperature, pressure, and so on. The fuel is pressured up to the injectors and then the injector is told when and how long to inject fuel depending on what the fuel map in the ECM is telling it to based on air mass, rpm, throttle position, and so on.

Not only that, but to add a device to measure fuel rate at each injector would add cost with no real added benefit when a simple (and lest costlier) computer algorithm will do even though it is not dead nuts accurate.

Exactly my point. All these crazy variables and algorithms and its still not accurate. Why not simply measure the amount of fuel coming out of the tank and be done with it. Not at every injector, just the one suction line out of the tank. Wouldn't it be spot on? Who cares about how much damn air, pressure, density etc. there is... how many gallons of gas is being removed from the tank and use that number to divide the amount miles the vehicle traveled and be done with it.

 

[tjfdesmo]

Besides all the WAGs going on in the fuel usage dept., I think the EVIC wildly overestimates the "fuel savings" when in MDS mode, which is an annoying joke of a gimmick in a 7K+ truck. This contributes to the reality gap.

 

[SouthTexan]

Exactly my point. All these crazy variables and algorithms and its still not accurate. Why not simply measure the amount of fuel coming out of the tank and be done with it. Not at every injector, just the one suction line out of the tank. Wouldn't it be spot on? Who cares about how much damn air, pressure, density etc. there is... how many gallons of gas is being removed from the tank and use that number to divide the amount miles the vehicle traveled and be done with it.

No, it would not be spot on. Like I said, you will have different fuel densities depending on the temperature. Different pressures depending on altitude. Different energy content of the fuel based on quality and ethanol content. You also have the vapor purging of the pumps fuel filter which may or may not be calculated. Lots and lots of variables and it isn't that simplistic.

Maybe these articles can shed more light on why.


Why Your Trip Computer Isn’t Giving Accurate MPG Readings

Your Fuel Economy Gauge Is Fibbing

 

[olyelr]

No, it would not be spot on. Like I said, you will have different fuel densities depending on the temperature. Different pressures depending on altitude. Different energy content of the fuel based on quality and ethanol content. You also have the vapor purging of the pumps fuel filter which may or may not be calculated. Lots and lots of variables and it isn't that simplistic.

Maybe these articles can shed more light on why.


Why Your Trip Computer Isn’t Giving Accurate MPG Readings

Your Fuel Economy Gauge Is Fibbing

I understand all those variables may change fuel mileage and such, but it still boils down to one thing... how much fuel was used? That and miles are the only two needed variables to figure out mpg’s, no?

If you know the exact amount of fuel that was used and the miles that were driven, you basically know the exact mpg’s by simple division. Its not rocket science.

And im not trying to argue or call you out, just kind of thinking out loud here.

 

[SouthTexan]

How do you determine exactly how much fuel is used down to a drop that is more accurate than the current way?

Keep in mind the mass of fuel changes with temperature while the volume may stay the same so adding some sort of way to measure the volume of fuel coming out of the tank will not be 100% accurate. The fuel will be colder at the tank and hotter as it gets to the engine so you have density changes there as well.

You also have different energy content between two fuels/brands even though they are the same volume as well. So you would have to know the fuel's density and energy content along with the volume coming out of the tank.

You can't use what is currently left in the tank because a there are too many variables changing the metering float like condensation, pressure expansion of the tank, changes in grade while driving, and so on.

Like I said, too many variables to be 100% accurate unless you want them to add more cost to the vehicle just to have your computer match your hand calculations. I don't care that much about it to pay more for a vehicle and I am sure most would agree.

 

[runamuck]

you guys have thought it out farther than I. I just figured the injectors will only pass a certain amount of fuel times the amount of time they run and the ecu would know exactly how many miles the wheels traveled during that time. now I've used all the brain power I had allocated for the day. going to need more coffee

 

[olyelr]

How do you determine exactly how much fuel is used down to a drop that is more accurate than the current way?

Keep in mind the mass of fuel changes with temperature while the volume may stay the same so adding some sort of way to measure the volume of fuel coming out of the tank will not be 100% accurate. The fuel will be colder at the tank and hotter as it gets to the engine so you have density changes there as well.

You also have different energy content between two fuels/brands even though they are the same volume as well. So you would have to know the fuel's density and energy content along with the volume coming out of the tank.

You can't use what is currently left in the tank because a there are too many variables changing the metering float like condensation, pressure expansion of the tank, changes in grade while driving, and so on.

Like I said, too many variables to be 100% accurate unless you want them to add more cost to the vehicle just to have your computer match your hand calculations. I don't care that much about it to pay more for a vehicle and I am sure most would agree.

I just think its being made a lot more complicated then needed. Who cares if stuff is expanding, or contracting, or vaporizing, or what the temp/humidity is outside, or if the tank gets bigger or smaller, or if your driving like grandma or an *******, or whatever the heck is going on.

It still seems like it boils down to two variables. The amount of gallons of gas used and the miles traveled.

I mean, does a gas pump account for all that stuff when it tells you that you just pumped a gallon of gas? Or does it just read how much fluid went through the damn sensor (or whatever it is)?

 

[SouthTexan]

An individual gas pump does not return fuel back into its tank. It also doesn't measure density and other things, just volume.

 

[olyelr]

An individual gas pump does not return fuel back into its tank. It also doesn't measure density and other things, just volume.

Exactly. Is there a reason why either of these are relevant? Isnt that all we care about here, volume?

Do vehicle fuel systems have a supply and return? Excuse my ignorance lol.

 

[SouthTexan]

Do vehicle fuel systems have a supply and return? Excuse my ignorance lol.

Yes, most do