Van5150

I just changed my O2 Sensors and after a gastank of fuel havent seen the increase in MPG that I expected.

I used to get 300 miles to a tank (yes 2.73's) and am down to 230 miles per tank. Does the PCM need a reboot ?

or, is there another sensor that can really effect MPG ?

Injuneer

There are at least 16 different long term fuel correction "cells" that need to be "rebuilt" based on any differences in the O2 sensor readings. Since each cell is defined by a range of RPM and MAP, you need to drive for a while to insure you have operated the engine in all the cells, and that could take more than one tank of fuel. Pulling the "PCM BAT" fuse would clear all the cells and reset them to 0% correction. Whether that would make things better or worse would depend on what the actual problem is. In the end, after a week or two of driving, you will end up at the same point whether you cleared the PCM or not.

Bad fuel mileage MAY be the result of faulty O2 sensors, but it can also be the result of the O2 sensors getting bad data, which can happen if you have excessive misfires, or an exhaust leak before the sensor. Each of those problems will cause the PCM to add fuel that the engine doesn't really need.

Van5150

Great information Injuneer. Thankyou.

I will clear it, and wait and see. I believe I do not have any such exhaust leaks. Thanks again.