I started a thread a little while back about building one and trying it. I have a 2000 F-250 Powerstroke that usually gets around 17 mpg. I installed it and pumped it in before the MAS. The first run with it was around 60 miles driving normal, didnt try to baby it at all. Milage went to almost 21 mpg. Good deal right? I reset the counter and let her eat for a full tank of fuel. At fillup, I got 15.3 MPG. I lost milage for some reason. I have a 120 amp alt so that should'nt have bothered it. There is a controller that you can buy or make that will control the computer to keep it from seeing too much oxygen and thinking its too lean. I have turned the system off until I can get my hands on one. I can tell you this tho, that thing friggin FLYS with the system on and yes, it pours black smoke out of it.