bad gas mileage in civic cx
 

WHen I first bought my civic cx about 2 years ago, I bought it in portland and drove it home to montana and got about 45mpg, now I am currently only getting about 30mpg all highway driving and worse city driving. I do have slightly larger tires on than stock and they are 195/55/15. I have also lowered my car slightly. Anyways I was wondering if you guys could give me any info on things to check, ect. and help me find out why I'm getting such bad gas milage.

Well, check your spark
 

Well, check your spark plugs, wires, dizzy cap and rotor, all that basic tune up crap. Does your car smell like gas out the tailpipe? More sluggish than usual? Leaking lots of oil type things?

Year and Sensors
 

Also, did you buy it new (what year is it), is it automatic, and how long has it been since the fuel system was cleaned? Also, any check engine lights, bad 0xygen Sensors, etc. Tell us everything that's changed since you got it. I doubt the tires would pull the mileage down that much, tho

Also, welcome to Gassavers!

RH77

sorry for leaving out some
 

sorry for leaving out some info.
Its a manuel 92 civic cx. Bought it with 80,000 miles on it, now it has 113,000. I've changed the spark plugs, axles, transmission fluid, dizzy, cap, rotor, oil every 3,000 miles and timming belt, I've put on new 15" rims, they are actually lighter than the stocks steelies though, and new tires for the rims.

no check engine lights, or gassy smells, doesn't burn any oil, it might be a little more sluggish than when I first bought it.

oh also, here in montana we
 

oh also, here in montana we have a lower octane for regular gas, (I think its 83) should I go with the medium grade that is 87 octane.

No check engine lights
 

No check engine lights though?

nope no check engine lights.
 

nope no check engine lights.

My next guess would be o2
 

My next guess would be o2 sensor or cat.

How would I go about
 

How would I go about checking those things, I'm a college student and have hardly any money so I can't really afford to just replace them if they arn't out.

I understand the money
 

I understand the money predicament, of course. Run a wire from the 1 wire on the o2 sensor and hook it up to a DMM, when you're driving it should read about .5 volts, if not the sensor is messed up most likely or the engine is pooped. I have a spare o2 sensor to send you if you need it. Cat you can just take off and look inside of and see if it looks clogged up.