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[hitecdan]

Originally Posted by ImSoAmish

Do love my techie toys.
OK. So if there is an error I just have to keep track of how much it is and mentally keep adjust the reading.
I noticed a 2.5 mph increase in my MPG after I changed the oil (unknown miles on the oil. Just bought this truck) and added some Diesel Kleen Cetane booster. I have a small % of my homemade Bio in the tank and figured the increase in MPG was from the additive which helped the lower energy content of the homemade Bio. My MPG is 20.5 at 60 mpg on level ground. It might show higher if I ran it longer at highway speeds. Wondering if this is reasonable for a 3.73 gearset. I have yet to do a fillerup hand calculation.

OK, now your getting way to techie. The overhead computer is in no way smart enough to account for the energy content of the fuel in your fuel tank. It's an algorithm the counts the number of times the injectors fire and their pulse width, rpm, and maybe a few other parameter. Then it averages all that over time until eventually it stays at 17.2 mpg (plus or minus 1.5 mpg). It also assumes the fuel volume of the injectors is the same, which they may not be. I don't even think a dealer can adjust it.

My overhead computer reads about 1.5 to 2.5 off depending on the driving conditions. It's fun to play with, especially after you get on the freeway and then reset the darn thing and watch it jump up to 65 mpg for about 3/10 of a second. Then creeps down to what ever. But for those 3/10 of a second I can dream I'm getting way better mileage then that stupid Prius that won't get out of the fast lane.