Definitely do a tune-up if it has been a while........o2 sensor, filter, seafoam, etc..
Also how about an alignment assuming that you're lowered.....if your toe is off that will rape your mileage by a lot........if you are using heavy wheels mileage will decrease also........try to accelerate softly and consistently and cruise no faster than 70mph
I also used to get 300 a tank.....that's 15 gallons, 2 gallons left at E........but I crept my way back up to 400 haha.....4cyl ULEV automatic too
I have an 02 v6 with an aem cold air cleaned the tb and used chevron. With shell mid grade i can get about 300 to 360. at one point i got 15 mpg. One time i got 250 miles to half a tank. these accords are confusing. I'm gonna get even worse once i get my racing headers installed
Wow, everybody's mileage bloooooooows. Non-ULEV 5spd here and I easily get 450-500 miles to the tank with A LOT OF WOT! I usually even break 250 miles before the needle reaches halfway.
I'd look into a new O2 sensor first since the ULEV uses a wideband O2 which is a lot more accurate than a standard O2 sensor. Second, I'd replace throttle body, intake manifold and exhaust manifold gaskets just to make sure you're not sucking in extra air or leaking exhaust causing O2 sensor readings to be off.
None of you are posting mileage on the car, which is very important. And you V6 guys... the J35 engine we have easily gets 23-26 mpg.