So I did a bunch of work to my 1997 Jeep's 2.5 engine over the last two years. O2 sensors, cleaned the intake, throttle body and the passages, the IAC, new valve cover gasket, intake/exhaust mani gasket, new exhaust mani, new cat, and a bunch of work to the chassis, namely ball joints and front u-joints. Put new tires on it, and a new battery, which helped too. I had been looking to get rid of or replace the Jeep because of horrible power and fuel mileage, even after all the work. I liked the look of the 31's and the lil'-lift, but it was a total dog. Flat on its face, needed 3rd gear and 5k rpm to pull big hills and etc. Very disappointing.
So the other day I was in Wal Mart, I decided I needed to replace the 1gal jug of Lucas Oil injector cleaner that was used up with something cheaper. Got some Marvels Mystery Oil instead.
As I've run three 19gal tanks with 8oz or double the suggested dose poured in through my Jeep, I've regained about 20% of the lost power. I generally buy regular BP gasoline which is a quality gasoline, and use Seafoam and the Lucas Oil sporadically. Even if my Jeep just needed consistent use of any old injector cleaner... Marvels Mystery Oil is the only injector cleaner/gasoline I've ever had direct attributable results with.
IMO, its worth a shot, I am extremely happy with the results, which were unexpected, and is the only factor I can attribute to the boost in performance.