I had one on my Tacoma, it was an 03 with the 2.7l 3rz, at first after I installed it there was maybe 1mpg better, but after rereading the install instruction I disconected the battery for the ecu to clear and then repowered the truck. After that according to fitch the ecu will remap fuel injection cycles for the better quality fuel. After 3 complete tanks of gas I hand number crunched and got a consistant 3.2 mpg increase. I have plans to install another on my truck now, but I'm waiting to save up and get the titan tank, the Glacier line kits and an airdog 2 all at once. So I can honestly say i reccomend the Fitch fuel cataylst. Oh and I also got on of the small drop in catalyst for the lawn mower and it did run better.