I have a bone stock 2005 cummins 3500 dually 4x4. I here other cummins owners brag about 20mpg. I have been hand calculating for a month now and the best i got not pulling anything was 17mpg. Has anyone used EFI live and can you post the numbers? I don't want to spend more on the parts then I can save at the pump either.

 

Yes EFI will improve your mileage! But you have to get an intake and exhaust upgrade too!

 

Being your truck is a 2005 EFI Live is not a option for you, the closest you can get to EFI Live is Smarty jr or Smarty PoD with UDC tuning. UDC is custom tuning for the smarty's and will simulate what EFI Live can do. For 2003-2005 Smarty with UDC tuning. For 2006-2009 EFI Live.

 

Just leave it the way it is. You're not gonna get much better than that unless you do a free spin hub kit. Which would take a loooooong time to pay for itself. The guys making crazy mileage claims are full of it.

 

Slightly taller tires and a tuner like Smarty to tweak the timing might help a bit. Your truck stock will make 20 mpg. at 55-60 mph, steady driving, in good conditions. Might do a little better with timing advance, but, average will not be that. Genrally, the average for an 05 is going to be in the 15-16 mpg. To beat that will take some parts and $$, these trucks are heavy, a brick in the air, and emissions tuned stock.

 

Does your rig have a manual trans or auto? 20 mpg is doable on an open highway, but ya gotta drive it like an old lady. It helps to have a free flowing intake and air filter, as well as a free flowing exhaust system. My truck will get 21 mpg according to my GPS, however the overhead "lie-o-meter" will indicate a steady 23.6 mpg (I wish). On long trips I will not go over 65 mph. In the city I will average 14-15ish (GPS). The Lie-o-meter will indicate 17-18ish (way optimistic IMO). I believe my GPS.

 

Auto. I don't go over 65 on the highway. How does a GPS calculate fuel milage?

 

It doesnt actually calculate fuel mileage, but does however indicate accurate miles driven. With this I found that my speedometer is roughly 2/tenths of a mile off, according to GPS. Hand calc is still needed to determine mpg, but its more accurate than going by the lie-o-meter. Its not exact, but pretty darn close.