mpg help

i have a 91 civic lx d15b2. Recently it has been getting piss poor gas milage. Normally even in winter it gets around 36mpg, but in the last 5-6 months it has dropped to around 22mpg. I figured it needed a tune-up, so i have replaced the spark plugs and wires, distributor cap and rotor, and any thing else i felt necessary to replace.
Does anybody have any clue what the problem may be?

The only other thing i can think of for a basic tune up that you didnt mention was an air filter.

Another good place to look is your cat, if it's clogged it can effect your MPG. A good resource is www.gassavers.org alot of guys drive Hondas there.

Good luck.

check tire pressure, change fuel filter

i have changed all filters and tires are in near excellent condition. i will check the cat though.

it doesnt matter what condition the tread is in.... Im talkin about the air pressure in the tire, as the weather gets colder in the winter, the air pressure in the tires will drop, resulting in poor gas mileage... I would check to make sure all the pressures are up to spec

i check my pressure almost every fill at the gas station and it is usually in spec. sorry for not giving a valid answer before hand. i did discuss the problem with my brother and he mentioned the possibility of slipped time. any ideas?

Change your oil..old oil is a power robber.

Timing could also be the issue.

timing, oil, tire pressure, although that won't make you lose 10+ mpg... check ignition timing, since you just replaced the cap/rotor, it could be off a couple degrees... recheck plug gap, check cam timing, check/replace timing belt.