Attention: TDR Forum Junkies That was a good one Bob, one of my favorites! 
Guys, the way the trip computer works is not based on fuel flow at all. Rather, its figures are based on throttle position, vehicle speed, and distance. There is a bunch of predetermined "templates" in the computer that relate to various throttle positions and speeds. Based on what your TP and speed are, it is going to display its best "guess" as to what your fuel economy is close to. Typically, it is high, even on stock trucks. However, add some injectors and a box, and the number displayed goes even higher. Why is this? Its because you are using LESS throttle to go the same speed. For example, when you were at 40% throttle stock, you are now at 20% with injectors and a box--but you are going the same speed as before. The computer thinks you are more efficient now, based on the predetermined values. Make sense?
My trip computer always displays an average MPG reading of nearly 30, which I know for a fact is BS. IF it worked by fuel flow, which it doesn't, my avg MPG diplayed on the computer should not have changed much.
The DTE thing is BS as well. Go by your odometer. That's what I do... Hit 700 miles, and it's time for a trip to the CFN for some good ol' #2.
Side note... The ECM does track fuel flow, in gal/hr. I have observed it while in motion with the INSITE software. Pretty cool. The Cummins RoadRelay gets its MPG readings using this feature unique to the VP44.
Guys, the way the trip computer works is not based on fuel flow at all. Rather, its figures are based on throttle position, vehicle speed, and distance. There is a bunch of predetermined "templates" in the computer that relate to various throttle positions and speeds. Based on what your TP and speed are, it is going to display its best "guess" as to what your fuel economy is close to. Typically, it is high, even on stock trucks. However, add some injectors and a box, and the number displayed goes even higher. Why is this? Its because you are using LESS throttle to go the same speed. For example, when you were at 40% throttle stock, you are now at 20% with injectors and a box--but you are going the same speed as before. The computer thinks you are more efficient now, based on the predetermined values. Make sense?
My trip computer always displays an average MPG reading of nearly 30, which I know for a fact is BS. IF it worked by fuel flow, which it doesn't, my avg MPG diplayed on the computer should not have changed much.
The DTE thing is BS as well. Go by your odometer. That's what I do... Hit 700 miles, and it's time for a trip to the CFN for some good ol' #2.
Side note... The ECM does track fuel flow, in gal/hr. I have observed it while in motion with the INSITE software. Pretty cool. The Cummins RoadRelay gets its MPG readings using this feature unique to the VP44.
I ran out of fuel once with my old chevy gaser and had to walk 7 miles back to the house at 3:30am with it raining. 
After that day I never let my Dodge go below an 1/8th of a tank. and usually when I fill it up I can put about 25 gallons in it, that mean there is 10 left to play with and it also keeps me from drawing the I TRIED TO BY-PASS THE CUSSING FILTER off the bottom of the tank. 
