I picked up 4mpg way back when I first got my xfi by trying 3oz of acetone each fillup ~8gal. I did that for about 3 tanks then quit using it. My mileage stayed the same and didn't drop. So I pretty much decided that it is a good injector cleaner for a car with 100k or more on it. It is also cheaper than those little bottles of cleaner.
As far as changing the way the engine burns the gas or whatever. My setup has an audio based knock sensor, wideband O2 sensor and Megasquirt computer with realtime display. I tried acetone again, this time the fuel/ignition systems were already clean and in absolute perfect tune before adding it. Nothing changed at all. No difference in the sound of the knock sensor so the timing didn't need to change and the wideband was showing a still perfect tune. My mileage also didn't change. So that little test also didn't change my mind and I still think it might make a good cheap fuel system cleaner.
So my opinion is that if you average 5 tanks on each part of an A-B-A test that you probably won't see a change, not counting the first tank of B and the second A to let the car adjust if it is obdII based. But if you have a car with a lot of miles or possibly a non ideal tune it might help out some. It is maybe possible it can make the gas burn a tiny amount faster/slower so if the timing is not ideal from factory or just out of tune you might get lucky and the acetone/gas mix can get the car closer to what it is currently tuned for. But tuning the engine and not bothering with the acetone seems like a smarter idea to me
