Join Date: Aug 2007
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I work for Hypertech and NOT PPE, but I can tell you why your DIC will be off when your program your truck.
Since we alter the fueling quantities and timing with the same tables that the factory uses the PCM knows exactly how much fuel is entering the engine. However since the DIC bases its fuel mileage estimates off of a theoretical model of the factory engine with a factory tune, the tuning changes from programming are not accounted for (even when using the factory tables with our changes). What this means is that the fuel mileage isn't being directly calculated directly from PCM fueling quantities vs. vehicle speed/distance traveled. And since the DIC doesn't base it's numbers on those things the changes to the programming induces errors.
Because our tuning does change the engine fueling at a given TPS/Boost/RPM/etc. that no longer matches the DIC model, thus causing an error between actual and calculated fuel mileage.
So it's not really something that you can account for in the tune.