Computer average vs. ACTUAL MPG - DISCREPENCY!!!

[gearhead313]

So here's the deal... I'm 2500mi into my lovely crz. I'm happily commuting 2 hours a day in her and all has been fine. I've been clocking a nice average between 41 and 45mpg on the regular depending on traffic and destination.

The last few tanks of fuel however, have given me a sour taste. I keep track of mileage in my H22A swapped EG civic hatch, which I've tuned myself on Crome and now get around 32mpg with a newly swapped accord 5 speed transmission. I take my fill ups and divide out the gallons taken to how far I traveled. Well I never paid attention to teh crz until recently. I noticed I never was getting the "429mi" or similar claims the ECO computer was giving me.

So, this past tank of fuel which I filled up today went as follows:

324mi traveled
1 tick on the fuel gauge
22mi indicated range
41.5mpg ECO avg since full (set to automatically reset every fill up)

Fuel taken: 9.27gal
(Same station, same pump, fill till click)

324mi/9.27gal = 34.95mpg !??!?!?!

Ok now... (calming down). Im not that angry b/c its bad mileage, since it told me they EPA estimate 31/37. What makes me angry is I feel like I'm being LIED to by the ECO computer! It seems like its calculating some tooty frooty average based on other things than what fuel is actually consumed. Man, I just dont like my new car LYING to me!! (i know how f'king dumb).


I just wanted to ask if anyone else has tried this and have come up with similar results. If not, I challenge you to real world calculate this and compare it to what it tells you. I'm just not happy anymore...

[kernk]

I always calculate manually - all my records at Fuelly are manual calculations. Sometimes they are close to the computer, sometimes a couple of mpg above sometimes a couple below, never off by as much as you see. My 2003 civic hybrid was always about 5 mpg high on the computer.

Are you running stock tires and wheels?

[cyeung]

Yeah, I never trusted the range calculation on the on-board computer to begin with.

429 miles / 10.6 gallons (fuel tank capacity) = 40.472 mpg
So, you can theoretically get that range, if you bled the tank completely dry driving non-stop. You really do not want to do that. The range also decreases because we have to stop and go, stop and go, ...

[gearhead313]

yeah im 100% stock.

Maybe the range is close, but regardless of how far you go, the mileage should reflect.

There has to be something to make it off so far.. I'm going to keep an eye on it and see how it goes.

[atteSmythe]

Do you trust the pump?

A certain station near me suddenly started reporting an extra 1/2 to 1 gallon on fill-ups. I've since stopped going there, and I'll be darned if the tank doesn't fill exactly as much as I expect it to now (8.5-9gal, depending on how long it's been since the fuel light came on)

[gearhead313]

I sure hope not! I only put Shell fuel in it. I've ran one out of whatever many tanks of 93, but the rest 87. My buddy actually works on gas pumps and says how complicated they are being completely computer controlled, etc... which also creates great storys of angry foreigners who own gas stations not understanding why when they break its such an ordeal to repair!

[ITEM9]

Different pumps can stop at different times too, so if a tank is filled with a pump that stops "early" followed by a tank that stops "later", then you might get "pessimistic" mileage compared to what the computer displays. Also different size tires will introduce error into the calculation; a smaller diameter tire than stock will cause the computer to read higher mpg than what you are actually getting.

[Scotty001]

Originally Posted by cyeung

Yeah, I never trusted the range calculation on the on-board computer to begin with.

Yea, the range is only accurate after 3/4 of a tank and if your driving under the same conditions - like on a road trip on the freeway.. which can be good. For every day use - its just a guestimate based on your last trip and conditions.. The only time I would use it or trust it is on a long trip..

[_JB_]

My actual mileage vs the computer at the worst has been 1MPG off.

[Scotty001]

Originally Posted by _JB_

My actual mileage vs the computer at the worst has been 1MPG off.

Yea.. I find the actual mileage at the end of a tank (as long as no resets) is pretty accurate..