I have a 2000 civic ex (actually a Canadian Si) 5 speed with approx 55k miles on it which i purchased a couple months ago. My gas mileage seems to be fairly poor @ about 20-30mpg highway, which is ALOT lower than my 94 got. Also, i have to downshift on almost any hill on the highway to try and hold 80mph, which my old civic never had to do. even when i do downshift, it still struggles. Its pretty damn shitty. When i went out to the mountains the other weekend i couldnt even keep up with old pickup trucks or other notoriously slow vehicles unless i kept my car redlined at all times. once i upshift it bogs big time.
Is there anything that could be causing this? here is a list of the things that i have done and havent helped:
changed plugs, wires, cap, and rotor
changed air filter
adjusted valves
checked air pressure in tires
changed o2 sensors
checked catalytic converter
checked for codes (none)


does anyone have any other ideas? this is driving me nuts. also, there is some soot on the very end of the tailpipe and it seems to run down the pipe to the muffler, kinda like its running rich. i double checked my plugs last night and they seem a little sooty as well but not bad.
Thanks in adance!

 

you try to check timing? jus a thought cuz my ek is doin the same right now

 

x1 and also your cat might be cloged if it has been running rich.

 

Fuel filter?

 

i have already checked the cat and it looks perfect. I will try to check the timing today and maybe change the fuel filter. I'd be suprised if it was that though because of the mileage but weirder things have happened.
thanks for the input guys