I too am in about the same situation. I have noticed the idle is a little rougher than normal for about the last month as well as lower fuel mileage. I purchased a code scanner as well after my check engine light finally came on Dead Link Removed . I was showing the same code 41 but it was only on the stored memory (continuous) codes. The check engine light started coming on after driving a minimum of 15 minutes. After checking the codes last week and resetting them, the light came on today for the first time since the middle of last week so I wanted to check it. I pulled over at a local park and WITHOUT shutting the engine off, (while the light was still on), I connected my scanner and it gave me a code of 42 (fuel mixture rich). This is known as a running code.
I then turned the ignition off and waited about 15 seconds and then turned the key on (engine not running) and read my codes again. I then had a code 41, "Oxygen sensor signal fault, switching not detected." When you first start the engine, the engine goes into a closed loop (set program) and it takes about 15 minutes before it starts reading the sensors like the O2. When it warmed up and found the signal to be out of range or not even there, then it turned the check engine light on. Whenever the key is turned off and then engine restarted, it takes 15 minutes again to start reading the signal.
Forgive me if I may sound too basic about this but I do not know what your mechanical ability is and I don't mean to offend you. The code reading consists of different steps. The first step is with the key on and engine off. It tells you any codes that are stored in memory (continuous), even though they may not be bad now...in other words, the problem could have been corrected in the past and still showing to be bad if the codes have not been reset.
The second test is with the engine running. When you do the scan this time, it picks up any codes that are CURRENTLY showing at fault at that immediate time...not an hour before or so but since the engine has been started this time.
I would reccommend resetting the codes, (read the instructions with your scanner to see how), resetting your computer by disconnecting battery cable for 5 minutes, and then driving for a while (1 hr+) and then rechecking them again. By resetting the computer, it will possibly straighten itself out after the problem has been resolved Dead Link Removed .
Last week, I also thought about the fuel pressure regulator so I bought a fuel pressure gauge from AutoZone ($35) and connected it to the test fitting on the fuel rail. It was showing the pressure to be within the specification so I kinda put the FPR out of my mind for the time being. I am now going to replace the O2 sensor and reset my codes and computer and see what happens.
I hope this may help you. I will stop here because I am beginning to confuse myself Dead Link Removed . Good luck and keep us posted.
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Ira
91 XLT 4x4
