Overhead Trip Computer

[rdes]

Just installed a D7159 puck on my 04.5 Dodge 3500 Cummins diesel. Drove 1700 miles towing a fifth-wheel trailer with the puck on the lower (60HP) setting. The trip computer was giving me wrong mileage performance and distance to empty data. I compared the computer mileage performance to actual fuel usage.
When I returned the switch to stock position, I got accurate data from the trip computer. What gives?

[mikel]

The DIC will often read wrong when a tune or inline device is altering fueling...

Thanks

[rdes]

What causes ther wrong reading? Doesn't the trip computer continue to receive accurate fuel consumption and mileage data from the sensors? If the P{owerpuck causes wrong signals to be sent to the trip computer, does it not also cause wrong signals to be sent to the engine computer?
Thanks

[ohyeahfriday]

Simply put, the trucks computer is being tricked by the Puck. The ECM is "tricked" by the Puck, as well as most boxes/programmers, because otherwise you would ever get the amount of fuel through the injectors that you need to see to make power. Right now, my overhead says that I am averaging 28-30 mpg, but I know better than to believe that.

To put it real simply, if you want to know your fuel economy, I suggest hand calculating, anything else will be flawed.