Thats what i'm saying! Can anybody really give a good explanation on this?

 

If I remember correctly, the Nerst(sp?) cell that forms the basis of the O2 sensor needs a fresh-air reference delivered to the "back" side; that is, the side of the cell that is not touched by the exhaust stream. The sensor functions as a relative device, so it needs something to compare the exhaust stream to. Rumor has it that this fresh air is supplied to the cell via the 02 wires (this rumor comes out of the service manual, FWIW).

If this is the case (and it seems logical to me, although I'm not very knowledgable about 02 sensors), then it makes sense that extending the wires via soldering would tend to cause a problem. Extending the sensor wires via a standard solderless crimp should be OK; that is, until the crimp joint is "clogged" with corrosion products and no longer allows the fresh air to be supplied to the back of the cell (and in all likelihood, corrosion will occur if extensive efforts are not made to protect the new joint).

The other possible failure modes with a crimp connection would be an open-circuit condition caused by corrosion, or possibly a situation where the copper wire and a dissimilar crimp material sets up a galvanic(sp) reaction and causes a small but significant voltage to be applied to the circuit. Situation #2 is made significantly more likely if the O2 harness wire is made of something other than copper (like stainless steel, as someone else mentioned), but I bet that situation #1 will be more likely.

FWIW, I've been running crimped-and-extended 02s on my car for over a year now, as my headers required them. I have been experiencing some issues recently with my 02 readings, so I think it's time to toss the extended 02s (they have a total of 90K on them) and pick up some fresh sensors and some "proper" harness extentions. This will be a much more robust way of extending the harness, in my opinion.