poor milage

hi i have an 1989 limited lesabre, i have been expieriencing poor gas milage lately . i have been getting 15-16 miles per gallon as compared to the 12 before i changed my o2 sensor. i just got this car on the road so i dont know if its always been this bad. i just dont know what else could be wrong. 29000 origional miles,and the air cleaner looks good, new fuel filter, pulled 2 plugs, 1 from front, 1 from back, looks great. no carbon build up. not black. no oil smell. wires are ok, not bad and not origional. same with plugs, not sure when changed but they are autolite 605's. o2 sensor changed b/c of check engine pulling code 13 or whatever oxy sensor code is. replaced milage increased tiny bit. i have people telling me the 3800 can pull 25-26 mpg city. and 29-34 hwy. what else could i check?

Not true on the mileage, 19-21 would be really good in stop and start. maybe 27-29 below 75 mph. This is with a perfectly tuned engine. Scan it and look for Baro radings, fuel trim readings, coolant temp readings, and iat readings all can affect mileage. Fuel trims will tell if it running too rich.

It all depends on the driving pattern. If you drive short trips and the engine never warms up to full temperature, you can expect 16-18 mpg around town. If you drive it on the highway continually at 70 mph it should get near 30 mpg. I rented an 89 when it was new while traveling and it got 18 around town and 30-32 on long trips. I have a family owned 94 with 55K and it does good to get 15 around town on short trips. The engine needs to warm up to operating temperature, and the car in overdrive to obtain the best numbers!

:sadwavey: