My car tells me the fuel economy I'm getting but it fibs by an mpg or two. It's a good trick by the manufacturer cause not many people will take the trouble to question the number. After all a computer is reporting it, must be the truth right? Anyone know what data is used to generate this number? Anyone seen this number to be low?

 

It's just an "Estimate"

 

i would guess that it is generated based on how many miles you go & your fuel flow/consumption rate...

 

generally its 1-2mpg MORE than what you are actually getting.



still nice to see

 

when i first view my mpg it tells me something waay different after i hit the reset button

 

I reset mine after every fill up, average bout 30 mpg. That seems about right for where and how I drive

 

I believe everyone knows this....

 

I ALWAYS check mine useing a calculator. Whats funny is it always gave me a higher number than what was true until last tank (i reset it every time i fill up too) and last tank it actually read lower than what i got. it said 28.something and i got 29.7mpg. I don't know what i am actually getting for mpg though because the damn speedo reads slower than what i am actually going! Not to hijack the thread or anything but if my speedo reads slow (i have stock wheels and tires) and i take it in to the stealership to get it changed, will it still be incorrect? I mean all they will do is reset it to stock right? which is where it should be now.

 

If you reset the gauge pretty often it will be decently accurate. The longer you go after reseting it the worse off it will be. It is just an estimate after all... and it's usually about 2 MPG off of what you are actually getting.

 

everytime ive done the math its been 1mpg off. exactly 1.0mpg off actually.. it will say im getting 28 when im really getting 27, etc.

 

Of course it does. its an average over the time since you last reset it.


If you reset it 5 minutes ago, and you're on the highway you're going to get awesome mileage. if you reset it and drive through the city, it will show terrible mileage.

 

i get 16mpg right now, lol

 

seems like the more mods the better gas mileage I get until WOT.. i guess its less strain on my injectors since they're bigger.. I can get an average of 36mpg

 

I have a question for you guys that do your mpg by hand. How do you know exactly how much fuel is left in the tank before filling up and how do you know exactly how much is in it when the pump clicks off? Also does your math account for the expansion of gasoline above 15c as that's what most pump meters are set to?

My money is on the DIC being more accurate than anything by hand.

 

I don't think they can do much about it. having a speedo that reads low is a good thing, you will show less miles on your car than you actually have and when it comes time to sell the car low miles equals money in your pocket! its not going to be a huge difference, but maybe enough to help you out by a few hundred bucks.

My gauge is usually 0.8-1mpg off, i can't complain about that. the auto guys usually say its dead on. its a great way to get some feedback on if your driving style is saving you money at the pump or not, even if its not accurate; It is consistent.

 

all you do is reset your trip odom next time you fuel, then after the next time you get gas take the number of miles on the trip & divide it by the # of gallons you put in your car.

example:

264.6mi/9.654gallons = 27.408mpg

 

There is room for error when doing that. You're assuming the shut off valve on each pump handle you use shuts off at exactly the same point, there can easily be a couple litres difference right there. Plus, that method leaves no room for thermal expansion of the fuel.

The DIC uses injector information to calculate mpg. Again, I'll put my money on the DIC.

 

how do you reset your MPG?? sorry for the dumb question ...

 

go to the MPG on the DIC then hold down the arrow button next to the i button, after a couple seconds it will reset..

 

ooo ok just like the oil one... my bad... thanx

 

my computer says im getting 24, however, im really only getting like 20

 

I have always wondered the same thing. Everyone claims that all the DIC calculations are inaccurate, but it is DIRECTLY CONNECTED to your engine. I agree with you, and think that the hand-calculation method is more of an estimate, and the DIC readout is accurate.

 

LMFAO, fav. quote in a while

 

I've only ever noticed no more than a 0.4 difference on mine when I figure mine out manually....

 

im on the DICs side...considering your computer is calculating injector pulse width to exact specifications and all it needs to do is divide that by # miles traveled....i would bet the DIC is more accurate than manual calculations