My wife's 2005 explorer has 125,000 miles on a 4.0. It has hardly any power, will barely pull it's own weight and mileage has dropped to about 5 mpg. This problem happened suddenly, as in, it was fine driving from work one day, she stopped at her mom's house for a bit and when she got in it to come home the problem had developed. About a year ago a similiar problem was fixed by having an o2 sensor replaced. Now though, we are broke and can't afford to put it in a shop. I could replace the sensor myself if I knew whch one it was (there are 4)and if that was for sure the problem. We live too far from an autozone to get a free diagnostic so i ordered a cheap obd-ll code reader from amazon but it won't work on the ford although it works fine on my cousins chevy. I have checked all the fuses and replaced the fuel filter. Today I unhooked all 4 o2 sensors thinking this might tell me something but it seemed to make no dfference in how it ran at all. What conclusion might i draw from that fact? I really need to get this fixed to go to work monday. Really appreciate any help you can give..

 

Why did the reader not work on the 05 Explorer? It is OBDII for all I know. If it does not work I suspect that the ECU or the wiring to and from it are bad.

 

I dunno, it keeps saying "link error". It does come on when I plug it in though and runs through all the protocols before displaying the "link error" message. I was leaning towards replacing the 02 sensors one at a time but I really expected some change in behavior when I unplugged them all but there wasn't, which probably means that it is running in open loop all the time if I am understanding what I've read recently correctly. Can anyone tell me what would cause this to happen?

 

Problem solved. . I took my last 60 bucks and bought a universal Ford O2 sensor and started switching them out. The second one I tried, the one on the driver's side in front of the catalytic converter did the trick.