another overhead fuel question

[GWaggoner]

OK, before getting flamed for asking again, I have done 3 different searches on this and have not gotten a good answer. My question is when you add a chip or other power additive, what is it exactly that makes the overhead mpg computer become so far off? My 03 555 is 3-4 mpg off from hand calculated mpg. There has been some discussion about this before but I can't find it. I am looking for technical answers.

Gary

 

[smokejunkie]

I don't know for sure if this is true for all chips but, the overhead measures mpg on the stock fueling program and can't compensate when you change that. There is probably a more technical answer than that but that's the just of it.