I recently purchased an 07 GT and have found that there is a 2 MPG difference between the computer display and actual, computer being higher. There is also a difference in fuel used with the computer showing a lower amount.
Is there a way to adjust the computer to get a closer to actual reading?

Thanks for any help - Mike

 

how long of a drive did you record this over? did you completely drain the tank, put exactly 5 gallons in it, drove it till it ran out, drained excess fuel and measured that against the 5 to calculate it? that is the only accurate way.

if you are just topping off the tank different pumps will stop at different times. sometimes i can fit up to another gallon in, sometimes it shuts off right at the top. so if you only measured over a few gallons you can easily have a 2mpg disparity if everything wasn't measured exactly.

example, you put 10 gallons in to fill it up, you used 3 gallons, getting 20mpg, driving 60 miles, on your odomoter, you fill it up but squeeze in 3.25 gallons, now it looks like you got 18.4 mpg. it makes it look like your onboard system said it used less fuel and you got worse mileage, but really, you just squeezed a bit more fuel in there than you had before.

the best way to make sure you dont get such big differences is to do it over the course of a month or so, trying to top off max everytime. inconsitencies will get averaged out.

 

The readout from the dash is normally not accurate. I would always trust pen and paper

 

The on-boards on our S197's are typically 1-2 MPG conservative but there are a rare few that are pretty close. My g/f's '06 V6 is usually within 0.2 MPG of the hand calculated figure.

No, there's no way to adjust it. Get yourself a cheap pocket planner at WalMart for about $3, clip a pen to it and toss it in the center console. Then use it to log your mileage plus any other maintenance that you do.

 

My 05 GT has been 1-2mpg off (on the high side) every tank over the last 55k miles.

 

If you have android based phone, there is an app called Mileage and it's free. You put in the info for each fill up and calculates and track stats on your mpg.