My girlfriends 90' TBI is getting horrible gas milage. Out of the last tank, she only got about 180 miles. That is terrible. What could cause this? When i get on it, there is definatly a good amount of black/brown smoke. I just changed the oil and ran some top engine cleaner in it. The air filter is new and so is the fuel filter. Also, it is not throwing any codes. Could bad O2's be the culprit? Any suggestions? Thanks.

 

how old is the 02 sensor???? when my o2 went bad, my car ran terribly rich, and my mpg was really bad.

 

Yeah, change the O2 sensor first, they only cost about $15-20, that car should be getting at least 250-275 avg. miles on a tank if it's tuned properly.

 

I am not sure how old the O2's are because she bought the car used. We put about 10k on it since the purchase and if I had to bet, I would say that they are the origionals and the car has 90k on it right now. I think that may be the problem. In theory, the car should be faster with new O2's, correct? Thanks.

 

yes, if you car is running that rich , the performance will suffer. and if your car has been running rich like that for very long, the cat may not be doing well either.