Lousy computer readings are bogus

Think about it. If the ECUs are calculating mpg using injector time
and distance traveled, that's making a huge ASSUMPTION about fuel
rail pressure and the actual volume of gas squirted. There's no
direct measurement sensor for fuel pressure, to my knowledge. So
that's one factor. Tire size and inflation pressure can also throw
off the "miles" you see -- my own car shows about 1% less distance
than the GPS does, for instance. Gas station pumps aren't dead
accurate, either, even if they *are* sealed by the local dept of
weights and measures -- they have a certain slop factor.
.
All of this can add up, and depending on if the effects add or cancel
can cause significant variation. Best to average over *many* tanks,
and hope that cancels the effects of pump gallonage variation, and
quit worrying about the video-game difference between 49.9 and 50.1.
.
_H*

 

<div class='quotetop'>QUOTE(ShellyT @ Jul 27 2006, 08:36 AM) [snapback]293152[/snapback]</div>

I don't think there is a flowmeter involved at all. I think fuel flow is calculated based on injector % open time. Those of us who have worked on performace cars know the kind of variation you can get between injectors, in fact one of the things people do to get the more power out of their cars is to get the injectors matched. I can easily imagine a %5 variation between injectors.

 

My MFD is more accurate than the non-existant mpg calculator that was in my last vehicle.

But, I also know it misses by about 2 mpg, and is always high.

So, I know that, and I move on... It's a Prius, not a segment of the space station.

 

The MFD is always a bit low for me. One or two mpg below my calculated. This does not include an occasional catch up tank when the outside temp is low.

 

My first post:

I have had a 05 Prius for a little over a year now and being an "Engi-Nerd" I have been keeping track. Over 10 months I have a discrepancy of about 4.4% (the display is higher than my calculations)... not too bad.

 

<div class='quotetop'>QUOTE(RyLewis @ Dec 16 2006, 07:03 PM) [snapback]363238[/snapback]</div>

My MFD is 5% higher than my calculations. During commuting this is not a problem. On longer trips through unfamiliar country I'll knock off 5% from the mpg then divide the miles by this number to figure the gas burned.

It is beyond me why Toyota can't accurately report the quantity of fuel remaining. It's a good thing they don't build airliners.

 

My car MPG on the screen is about 6.5% to high. That stinks in such a car that is fairly advanced. But irregardless I have avreage 49.2 MPG (7187 miles with using 146.096 gallons) since new from dealer. The said thing is that I have only had the car 10 weeks and still have one more long trip planned this summer (wedding) plus my 400 mile weekly commute.
PS is there a place that explains the abbreviations used on this website?

 

Here's the results of my 07 Prius

50 tank refills calculated: 50.72 mpg


MFD........................... 51.6 mpg

 

http://priuschat.com/forums/prius-main-forum/12452-acronyms-abbreviations-glossary.html

a lot here....

 

Did you buy most or all of that gas from one gas station? Could be their pumps are off just a tetch.

What other car would give you 49 MPG? The sad thing here is your 400 mile weekly commute :_<