Most of you, it seems, based on reading the boards, seem to have an optimistic MPG display on your FEH. For me, that's only half true. I've noticed for some time that my MPG display is often slightly (generally less then 2 MPG) optimistic from by hand calculations during the witner, but is generally slightly (generally less then 2 MPG) pessimistic during the summer via the same methods. This was true last year, and it's very true this year.

Odd, isn't it?

 

I'm about to reach 20K. I think I'm going to add Display MPG and General Temperature to my log book so I'll have some solid numbers to discuss on this topic.

 

Sheesh, YAEPTWA--Yet Another Equinox Problem To Worry About? Not only do I have to worry about
balancing an egg on its pointy end on the hood of my FEH, satellite dish Sun Outtages, the
Eratosthenes experiment for K12'ers, etc., now I've got to worry about my MPG display actually
being correct twice a year? :-)

Thanks for the interesting observation, Prof. Rich!

P.S., While I haven't logged display MPG and temperature (El Lay, unlike Michigan, is temperate
all year long), I remember the display MPG from Monday's fillup being pessimistic:

06 FEH w/ 17K miles - Display MPG: 40.4, Calculated MPG: 42.03 (245.1 miles, 5.831 gal.)

 

Hi Rich --

Do you re-set your FCD only when you fill your tank? I vaguely remember hearing a discussion, at HF2006, about the number of data-points it could track. Not knowing what a data-point would be, I didn't really listen too closely , but I remember the number 200 being tossed around. My FCD has never been equal to my hand calculations either, but I've never kept track of whether it's been + or -

 

Yeah, I reset it every tank. It's supposed to store the last 2000 data points. While I've heard that over the course of a tank for most of the better drivers (who have longer tank ranges), it gets increasingly inaccurate. However, this could actually tie into the causation. However, one thing that's interesting is that usually the FCD isn't that far off, which seems rare as I read from other users.

During the winter, I can't get as far on a tank due to diminished MPGs because it's cold. Therefore the 2000 datapoints are at or slightly optimistic like other users report due to it's nature.

During the summer, I can get, say an extra 168 miles to a tank. That creates a lot more data points and perhaps the FEH can't keep up with all of them, and causes in the end a pessimistic tank?

I don't know, that's a complete guess. This is the first summer I've had my SGII, and it seems to be pretty darn close to the by hand calculations.

 

Whats your Fuel fillup correction on your scan guage? Mines set at 6.6% (I averaged 4 tanks by hand last month to get that number). For the first part of a tank it matches my NAV pretty good. (off by <0.3 MPG). After a while though (after the points run out?) it diverges... It matched for more than 40 miles though.

I'm wondering if I redo the tank average number for my fuel fillup correction in the winter if its going to be different than 6.6% and I'm wondering if that tells us something in this mystery.

 

Makes sense to me On my 51.6mpg tank, I kept re-setting the FCD when the trip odo showed >200mi., but on this tank (so far), the FCD & SGII tank mpg have been staying within 3/10mpg of each other, so I think I'll try leaving it alone for now

Just out of curiousity, does anyone know what constitutes a data-point?