Has anyone ever used a bottle of fuel injector on your car to increase mpg? I'm thinking of buying a bottle of STP complete fuel system cleaner (for about $6) and a bottle of fuel injector cleaner (for about $3) . I plan to buy it and use it on my next oil change, about 500 miles from now. Any one use this brand before? How good/bad were the results?? Anyother recommended brands that arent too expensive, but will give the same results and are around the same prive range?? (ive seen other brands like prestone for like 75 a bottle but i dont trust putting that stuff into my engine. And i heard of bg44 or something like that but seems to costly for me.)