Surprised With Fuel Mileage!

Well the dash deal is inline with the Qualcomm sensor trac's ...I'm a company driver ...
i don't carry pencils & paper lol

 

The qualcomm mpg is reading it off the ECM, which is what you dash display is reading. That is why they are inline with each other. You still need to do pump to pump calculations to find out the exact mpg and how it compares to the displays.

 

I'm sorry to disagree Bill, but nothing is more accurate than tracking by fill ups, I do track my miles by the GPS which is more accurate than the speedo and anything else, it eliminates the tire wear factor or any discrepancy betwin the ECM and the speedo.

 

Ok stop and think through this. You have computer that controls fuel used down to the droplet. That is the data that is used for calculating MPG on your truck. Now biggest factor in error is going to be how accurate your speedo is. And you are correct. Using a gps (but one that also can calculate for elevation) is going to be the best way. On my truck (speedo was 2 mph fast at 60 mph) I used the mileage from my RM 710 and fuel used from the computer.

But using data from fill-up to fill-up has far to many factors to be even close to accurate. Sure, old days is was the only way to estimate MPG.

But look at some math. A truck that gets 6.5 mpg getting 120 gallons of fuel. Just a 2 gallon difference will change the MPG by .1 of a gallon.

Now all the factors on fill-up that will give you 5-10 gallons variance from fill-up to fill-up. What angle are you one (even a slight angle will allow for more or less fuel, how fast it breaths if topping off, how fast the pump stops, ...). Human factors - do you have to pee, are you running late so you don't take the time to top off, maybe there is a line and don't want to take the extra 5-mins to top off, having to fuel in an expensive area so you don't take as much. Or pump factors - does that pump shut off sooner than others not allow you to really top-off.

Now over time all the various factors will have less and less of an impact to the point that they are statistically insignificant.

But the bigger issue is if you are seeing that your computer is off then you are having a problem. I had a bad ECM once and it was showing 1 mpg lower than what I was getting at the pump. Once replaced it was accurate and fixed a whole bunch of other things that ended up with better MPG.

 

If you want an overall average you are correct. Pump to Pump tracking is the only way to calculate in idling and other factors, but if you want a "driving" average then the dash is the only way to know that. When trying to find the "best" speed to average then the dash ECM is the deciding factor, sicne you can not calculate that with a pencil, but you can get it pretty close.

I prefer to do the pump to pump method myself as it shows me just how much fuel a run is costing me out of my pocket, and how much an APU would be saving me LOL

 

On my 09's after 450,000 miles the difference between the computer and gallons/miles was less than a 10th. On the 11,12,13's it is in the 100's. With the 07's and earlier the difference was so large the only way to track was gallons/miles.

 

I tend to follow my IFTA fuel mileage more than the computer or the pump to pump.

Gives me better overall average over all miles driven.

And in 5 weeks, that's coming out to around 6.7 mpg. And that's with the silly error of not putting a new fuel filter early enough.

 

all of those reasons are why i posted a monthly total and avg. One day at 6.5 and another at 7.6 is meaningless
If i could only get 300 mile runs from gary to indy every day I would get great mpg

 

I get much more m.p.g. since I do the same runs, except I now start at night, where before I started at 7 am. now I leave out at 230 am set the cruise at 60 & get both loads off the same day. getting almost 2 m.p.g. more but as far as the pump fill up. well I can fill up & then put 5-8 more gallons in if I want. I can always put less or more to get a better m.p.g. I always top off. and I mean top off. that gives me the most accurate reading ,I can think of. I have no dash reading of m.p.g.