I used to get 30mpg on the highway and now i get 10mpg. I've done everything I can think of to fix the problem but I still get 10mpg. I've cleaned the airfilter, changed sparkplugs and distrib cap, used fuel injector cleaner. What else is there? Maybe the timing was thrown off? Any help is appreciated

 

Oxygen sensor.

 

fuel filter. bad fuel injectors. clogged cat. spark plugs

 

o2 sensor

and everything that guy above said causes pretty extreme issues with the performance of the motor so i wouldnt worry about any of them.