I just drove 1495 miles from New Orleans to Flagstaff,AZ in the Honda Pilot.I used a scanguage on the trip for the 1st time.
My problem is that the Scanguage read 3-4 mpg HIGHER- than the actual mpg.Another little rub is that the Scanguage was reading much closer in mpg to what I expected to get.
My trip mpg was about 19.5 mpg. When we did part of this trip last Aug we got 24 mpg on the last 1000 miles of this route.We got about 19 mpg on that part of the route this time.
Now this time I "topped up"-I don't think I topped up" last time.I was watching to see if I was pumping gas thru the overflow-in which case it would be all over the concrete-it wasn't.
I wonder if overfilling it could have caused significant amounts of gas-at least 1 gallon per fillup- to have sloshed out enroute?
Any ideas?? I really asking 2 questions-
1)Why was the Scanguage so far off-almost as if I was losing gas-sloshing it out,or maybe having an actual leak-no odor noticed, no obvious leaks.
2)Why was my MPG so poor? Maybe the wind was unfavorable-hard to say, but there is always lots of wind. My sparkplugs are 36000 miles old, but usually plugs last a heck of a long time now.
All ideas welcomed.We were thinking of taking the Prius, but we take sooooo much "stuff" 2 adults, biggish greyhound,kitten,air mattress,mtb etc, that there is no way the Prius could carry all of it.
Help.Charlie

....If you think being 3-4mpg off is bad for ScanGage I is bad, you would have a heart attack on the 5-speed Insight. Since it can't deal with lean burn, it's frequently off by 50mpg or more - useless.

I do enjoy the non-fuel consumption readings however....

61.5mpg lifetime - 82mpg in recent months

Best Run >
www.cleanmpg.com

"fanatic" is what the lazy call the dedicated

I suppose fuel could have been lost to the EVAP system, but an entire gallon per fill seems like an awful lot to lose that way. Maybe your alignment is off? That can be the case even if a car feels like it's OK. Have you double checked the tire pressure? One could have a slow leak that's dragging you down.

My ScanGauge originally did the opposite, reporting 6-10% below actual fuel efficiency. Adjusting the correction factor on the "Fillup" screen based on my receipt has given me relatively accurate readings ever since. That's the easy part of your problem to solve.

If I'm not mistaken, Flagstaff is WAAY above New Orleans' elevation. Is the 19mpg a one-way figure or the round trip?

Guys, thanks for the response.Yes, a 50 mpg would be a huge shock.

Yes,NO is at sealevel +- 4-5 ft.Flagstaff is about 6900 ft, so it is uphill.The 1500 was one way.I left a few things out to make it simpler,since it is still 2 problems-1)Scanguage reads close to 20% too optimistic; 2)My MPG is about 2-4 less than it should be.
The other factors
1)Yes it is uphill, but it was uphill in Aug(evac) when it got 24mpg on the last 1000 miles(DFW to Flagstaff).It would have been even lower than the average since the worst tank was a 15 mpg from Alb-Gallup.
2)I move the scanguage from car to car-Pilot,Prizm(Corolla),Prius. I don't "tell" the scanguage I'm doing this-meaning I don't do any adj.;I just pull it out of one and plug it in the other.Heck, it is just taking fuel flow numbers and speed numbers and dividing.How tough is that?It is as if it is either misreading fuel flow, or I am losing gasoline??
3)My airfilter was old(36000 miles).This could hurt actual mpg, but it shouldn't hurt the Scanguages ability to read and divide?Same story on spark plugs,PCV valve etc.I've changed the airfilter,and will change the pcv-probably won't bother with the plugs.
4)I have done this trip many times in 4 different vehicles.The east to west leg is always about 1.5 miles less than W-E.A tiny bit of this is the 7000 ft drop.I'm fairly sure that prevailing winds across AZ,NM,TX are the major factor in the 1.5 mpg difference.
5) I have oversized tires(long story which could-probably do-but not 100% sure they hurt hy mpg).I have corrected for the size.I had these same tires on for the return trip in Sept.It was 24mpg(corrected) on the return trip in Sept 2005.
6)I'm not so sure the prevailing winds in Aug Sept are the same as they are in early June.
Well,what do you think.The poor mpg certainly could be because of dirty filter,bigger tires,unlucky winds,and a bit of slosh evaporation.. Could the switching of the scanguage have "thrown it off?".I confess,I really didn't spend much time reading the scanguage manual.
Brick-I didn't think the evav system vented to the outside? The tank has an overflow for liquids, but I didn't think there was anyway for vapors to escape?
On the trip home I'll have a clean filter,and will stop filling at the 1st "stop".I think I was losing fuel; maybe the evac system/slosh.I was stopping at the 1st stop last trip.I didn't do it this time because we were driving at night in remote areas.I was concerned with range.I added at least 1 gallon after the 1st stop.(8 fillups-we stop fairly often-walk dog etc)
Thanks,Charlie
PS I gave you corrected mpg.The distance is 1495 miles(many trips,same route,different cars-all read within 8 miles of 1495)-my trip meter read 1418-about a 5.4% difference.It is exactly what I expected with 245/75 x16 vs 235/70 x16- roughly .75" taller. I used ~76 gallons.

Ahh, there's your problem. The ScanGauge does need to make some assumptions since it isn't measuring fuel flow directly. (Don't ask me for details...I don't know.) You need to go into the Setup and change the parameters to match the engine of the vehicle with which you are using it. It is probably set to gas by default, but the displacement may well be wrong. The procedure is detailed in your manual if you have it handy. If not you can probably figure out out on your own, or one of us can help you out. (I would just walk you through it now but I don't remember the procedure without being in front of it.)

Brick-thanks. If the gauge think I'm in the Prizm or Prius,and it actually reads flow to a single injector and them multiplys by 4 instead of by 6, then it would say I'm using 2 gph instead of the 3 gph I'm actually using.The error could have been that large- roughly 30 mpg instead of actual 20 mpg.I only used it for an entire tank once ,and the reading was about 24mpg vs actual of about 15.5 mpg.
I will go play with it.
Thanks for the help.Charlie
PS I was a lot more puzzled about the error than the actual poor mpg(19.4).I had plenty of reasons to get poor mpg(dirty filter,wind,old plugs,didn't D/C CC on uphills like I usually do,less roadwork with 45 mpg speedlimits).