Before you start I did search the forums and couldnt find any help with this problem. I have a 2004 EX with 145,000 miles. When I first got it was was hitting mpgs in the 30s. My last fillup brought me 21 mpg. Here is the fuelly chart: http://www.fuelly.com/car/honda/civi...gepoge1/299035 along with mods in notes that I did during that tank. I also have timed my 0-60 at 12 seconds which is terrible compared the the average 8 seconds. I miss my mustang right now cause it was 7 seconds. And the Mazda 6s that I passed on to get a civic got 6.5 seconds. Any idea what is causing this problem? The spark plugs are the Denso Platinum TT and I put a Fram air filter in on this most recent tank which was my worse tank(old filter was also FRAM but wasnt the Extra guard one. Old one had pollen buds clogged in it though)

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Stock Civics have never been champs at sprinting. 12sec is not surprising at all. Mustangs and Mazda 6's have larger engines than you probably do. Now if you had a turbo or engine swap, that's another story. Do you get top tier gas? Any additives besides the SeaFoam?
Oil is good?
Unrelated, but timing belt is good?

did you go through essential tune-up mods (or similar name thread) made by Gearbox?

I used STP once cause I used it with every fill up in my mustang. I am gonna try non-ethanol gas for my next fill up just to see if I notice a difference. Last time I filled up I used Exxon. Oil is at 6000 mile mark on the synthetic so gonna change it soon. Initial acceleration is awesome. It is the 30-60 that seems to lag a bit. But I am up to 30 in no time. I noticed the RPMs are slowly being able to hit higher.(I almost redlined the other day on an automatic taking off full throttle from a stop sign to test it). But that may be me gettings used to it more and knowing its limits.