i put some chevron techron in mine about every other to 3 oil changes. does it help? i dunno just do it because i've heard good things. it did seem to make an improvment in my moms explorer though, did it at about 70k miles for the first time, so maybe after so long it did really help. its supposed to clean out carbon desposits and such in the cylinder itself also.
also zetec, keep reading and learning here. i have been and its worked wonders. i know the zetec is a great motor for FE, as i had a duratec (2.3) for some time and i was able to squeeze around 35mpg out it, even before knowing some of what i do now. you'll be over 30 in no time
