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118 Posts
I found the 3-5% error as well. BUT I found the error to be less the more I baby the car. IE, if I get 37DIC on my ECO because I have been driving aggressive, it might be 35 calculated. Last 2 tanks I drove more carefully and was only off .5MPG each time @40MPG. I would assume that when you put your foot in it the engine is using way more fuel than the computer thinks.
