O2 Sensors on '95 GM

Hi!

I have an '95 GM Dual Exhaust that I received with 185K on it. Since I did not buy it new it is difficult to know what parts have been changed and when. I have noticed the gas mileage is not great (according to the Digital readout approx 15-17 city). Did plugs,wires, MAF cleanout and the brakes/emergency not binding. Also cleaned EGR ports and replaced TP sensor. There is no CEL and no codes but I have heard of "lazy" O2 sensors playing havoc with gas mileage. What if any are the cost/benefit advantages, gas mileage wise, of just replacing all four sensors? Rock Auto has them for approx $43 each, without shipping.

Since I am suffering from a serious illness I am not thrilled about crawling under the car to replace them if there will not be a decent benefit. Don't want to pay the labor for something I can do so hence this question. Thoughts please????? Thanks....MB

Hello MB. Glad to see ya. Check this link. Your vehicle is in range. You need to do the mileage the old fashioned way. Send me a note so I know what is happening.

http://www.fueleconomy.gov/feg/bymake/Mercury2005.shtml