You can get O2 sensors from AutoZone for $38.99 for Bosch or around $58 from Ford. I have just replaced 3 in the last 2 months on mine. I know you are wondering how. The first one I replaced was bad. I know this because as soon as I put it in and drove it, 10 minutes later, the light came on again. I made a test harness and plugged it into the O2 harness and found I was not getting a changing signal like I should. I took it back and replaced it. The light came on once with the second new one and that was the first day. I later checked it and it was giving the voltages that it should. About 2 weeks ago, the light started coming on again but not everyday. I got mad because I figured I had another defective sensor so I took it back to AutoZone and they refunded my money. I told them I had better things to do than keep climbing under there and changing sensors out. I went to Ford and bought one from them. About 2 days later, the light came on again. Did I mention that I had checked the codes before and had one for a bad O2 sensor at first? After I changed it, I never got that code again. It was just saying the mixture was too rich or too lean.
A couple of weeks ago, while sitting at the drive-up at my bank, I noticed the engine would surge at idle. It would go up 200-300 RPM and then back down. It did this continuously until today. I got my fuel pressure gauge out and checked my pressure again, like I have a couple of times since the O2 deal was going on. It is supposed to read around 30-45 at idle. It was reading 38 just like it has been before. Suddenly, it jumped up to 70 and fluctuated and never dropped back down. Before doing this, I disconnected the vacuum line from the fuel pressure regulator and had NO fuel coming out of it since I suspected it was letting fuel dump back into the engine thru this line. I thought it was OK because it was dry. When I saw the pressure jump, I replaced it. Now I have more power and engine is idleing smoothly, even at 170K miles. When I restarted it after replacing the FPR, I floored it once and covered the ground with carbon that blew out of the tailpipe.
Moral of the story...just because it may test to be good, it may not be. I was just lucky to get it to finally surge while I had the meter on it. Since the early models do not have a engine code specifically for the FPR, like mine, the O2 sensor is many times the code you will get. Another thing to consider is that when the FPR does go bad and stick like mine did, over a short period of time, the O2 sensor can in a sense be "fouled out" by the carbon from the excess fuel being burned and cause it to read as being bad. That is what I think happened.
If you pull your O2 sensor out and the end is very black, do yourself a favor and replace the FPR first before replacing the O2 sensor. If the FPR was at fault, after replacing it the exhaust may possibly get hot enough to burn the carbon off the O2 sensor and it will start working.
Been there...done that.
BTW, my check engine light would not come on until after driving for 10-15 minutes at least. I think what happened at AutoZone was that I did in fact have a defective O2 sensor at first and the second one went out because of the FPR.
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Ira
91 XLT 4x4
Once I thought I was wrong, but I was mistaken.
[This message has been edited by Ira (edited 03-22-2000).]
