O2 Sensor Problem!!!!

Ok.... Here is the deal. I have a 97' SW2. I keep getting a code P0143 on my code scanner. Swaped the exhaust manifold for the exhaust headers and downpipe from a 91' . The O2 Sensor from the 97' would not fit in the headers from the 91' so I got a new O2 sensor for the 91' headers. I have checked the voltage at the sensor. Fluctuates between .78-.89 while engine running. With the harness connected, it reads 1.01-1.09 and is pretty steady. The code is: "No activity O2 Sensor CKT. Bank 1 Sensor 1" Which is the front O2. Im sure the O2 sensor is fine. I have also replaced the heated O2 after the cat just to be sure it is ok as well. No matter what I do, I keep getting the code.
Can anyone tell me if, (for some strange reason that would not make any sense whatsoever) if there is any difference in refrence voltage for the 97' sensor and the 91' sensor?? From what I have read about O2's they all work the same (one wire all wor the same as one wire). The book I have says it should read 0.5 on harness KOEO. (Key On Engine Off) and the sensor should read 0.1-0.5 warmed up. I will check reading again and post them. Maybe someone with the same engine can check their readings compare with mine. Thanks in advance guys. As you can tell I am at wits end here. You can email me at [email protected]

So sorry my friend. I have looked into your future and it does not look well at all. My sources tell me that you will soon be in a position to be striking your O2 sensor with a large blunt object. Shortly after that the sky will fall and you will post a quarter mile under 30 minutes. Good Luck :)

Very funny. I would like anyone I DONT know to reply with helpfull information.