i do agree the best way to clean fuel rail is is pressurizing to do it properly but the additives do some cleaning for some1 who cant do it themselves.i use the additive(any 1 )to safely clean my throttle body (put on rag)watch the black/grey goo wash off,(so by itself must wash a little)better then nothing was my theory(under 10.00 worth a try).she mentioned that she keeps track of her mpg all the time and it certainly has gone down alot even though she didnt say what it was.