YUP.... no kidding ... I just got my AFE intake, Bully dog power pup and 5" magnaflow exhaust w/ cat intact...well according to the DIC anyways thats what it read...... I took my hunny out of town for our anniversary this weekend so I fueled up sat AM reset the DIC and drove 110 miles on the highway and when I arrived at my destination I was reading 26.0 mpg.... is this possible??? When I fueled It only allowed $50 on the card so it wasnt quite topped off so there is no True way to confirm if the DIC was way off cause I couldn't calculate manually but by rough/estimated calcs it's pretty accurate! is this standard or did I just do really well???

When you add a performance enhancer (programmer OR harness box) your DIC mileage goes out the window. Your DIC (no pun intended) has no idea what your mileage is at this point. You must hand calculate your mileage if you have other than stock programming.

I have heard this before but haven't seen why it is this way. Why can't the power adder be built to work in tandem with the DIC as opposed to it?

the DIC doesn't know of the different amount of fuel that's being applied by the various power enhancers so its off. to date i don't know of anyone who has tried to re-calibrate it. i've never had one that was 100% accurate, even running stock which is why i've always calculated mileage by hand.

When you add a performance enhancer (programmer OR harness box) your DIC mileage goes out the window. Your DIC (no pun intended) has no idea what your mileage is at this point. You must hand calculate your mileage if you have other than stock programming.

:exactly:
How much of the wide variation in fuel mileage is because people assume the DIC works right? Man, it sure does get old seeing all the widely different MPG reports around here, mostly because people have programmers (which lie to the DIC on the fuel usage) or different size tires (which lie to the DIC/odometer on the mileage actually driven).

I routinely get about 15% error in my MPG (more when towing) from the DIC compared to actual calculation with predator 40hp tune (lowest) and it just gets worse from there at the higher tunes...and from the predator diagnostic readings, I assume it could be worse depending on how much you have your foot in the throttle (since the difference between the stock fuel and tune fuel delivery seems largest when accelerating or heavy loads).

Just filled up..
212.7 on the trip odo... 17.35 gallons in... that's 12.25mpgs...
DIC said 16.5.
I use a Diablo Predator on 60hp setting.
Truck only has 7500 miles on it.

ok folks,
before we get our pannies in a wad, check out The Diesel Place rules for computing MPG using JJ's formula.

http://dieselplace.com/forum/showthread.php?t=29531

ok, now that you have had a chance to look at the old thread that you cant post in any more, i have started this new thread on MPG's. Enjoy.

http://dieselplace.com/forum/showthread.php?t=37609