Oxygen sensor dead

I have a 90 Ford F150 pickup. I bought the truck a few months ago, and knew it had a few problems. I did several smaller repairs myself, but I just had it in for larger repairs and spent quite a bit on
getting the 4WD repaired along with some other repairs. The mechanic showed me a hanging wire that is supposed to go to the Oxygen sensor. It was supposed to cost another $70 to replace it, so I told him to go ahead. The next day he called and told me that he can not change it because the exhaust crossover pipe is too weak, and has been patched with clamps and tin. I saw what he was talking about with the patch. Changing that crossover pipe would cost another $300, and could cost more if other parts of the exhaust system can not be reused. In the end, this would end up costing upwards of $500. I dont have that kind of money at the moment and told him to just leave it, because it runs fine the way it is.
I know that this exhaust crossover pipe will eventually need replacement and it's a little noisy now, but I can only afford to do one repair at a time. I thought the cost of that crossover pipe replacement was excessive, so I thought that I might just do it myself. I called several parts stores, and they all want around $250 just for the pipe. I nearly died when I heard that a lousy piece of pipe costs that much, even if it is welded in the middle. It turns out that the pipe included the catalytic convertor as part of the pipe. (which if you ask me, is assenine). My truck does NOT have the cat.conv. as part of the crossover pipe. It's separate and clamped on. They do not sell the pipe separate. I called a muffler shop and they said that they can probably make me a pipe for much less. So, this is what I will probably do when I have the cash again.
Anyhow, my question is more about the Oxygen sensor. I have had several people tell me that I am going to get poor gas milage without that oxygen sensor. Yet the mechanic that worked on my truck told me that on an older truck like mine, he would not worry about it. Who is right? To complicate matters more, someone that worked as a mechanic for years, told me that there is a way to jump the wires on the plug that goes to the Oxygen sensor, and that will make the engine think it's installed and I will get good milage. However, he said he could not tell me which wires to cross and no longer had access to some notes he once had about that.
Does anyone know anything about this wire crossing thing? Just how much milage will I lose without the Oxygen sensor? Or will I lose any at all?
Robert
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On Sat, 08 Dec 2007 07:33:35 -0600, snipped-for-privacy@yahoo-gmail-hotmail.com wrote:

still affect mileage and performance to some degree. Crossing any wires will NOT fool the computer because the O2 sensor is a "battery" that generates voltage according to the difference in O2 between the sensed and ambient.
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clare at snyder.on.ca wrote:

I bet you won't lose enough mileage to make up the $250 in crossover pipe...
how much longer are you really planning ot keep that truck...
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Ummmmm... did we forget that lost gas mileage is cummulative? Thge longer he keeps the truck, the more it matters.
Did we forget that the default is to a rich mixture? Possibly rich enough to wash cylinder walls and lead to premature engine wear?
I have no emperical data... and neither do you.
Broken is broken... is there any other way to explain it? Without sufficient funds to repair the truck properly, my best suggestion wont be well received
The O2 sensor is the "feedback" component of the system. If the PCM is to deliver the correct fuel charge and the best ignition curve, this sensor needs to report conditions accurately.... But I'm a mechanic and what the fuck do I know?
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On Sun, 09 Dec 2007 10:42:02 GMT, "Jim Warman"

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On Sun, 09 Dec 2007 13:39:02 -0500, clare at snyder.on.ca wrote:

I realized that, since there is outside air entering the pipe. It obviuously leaks since it's noisyer than it should be.
But here's another question. If I have a muffler shop make me a new crossover (one said they could do it for much less than a factory replacement), can they weld in a place to thread in the O2 sensor? Does it need to be exactly in the same place on the pipe?
Thank you
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On Sun, 09 Dec 2007 18:31:17 -0600, snipped-for-privacy@yahoo-gmail-hotmail.com wrote:

possible to the original but it is not terribly critical. A heated O2 sensor is much more forgiving of location. Within 6 inches should be OK.
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If the pipe has been patched up with tin and clamps, its probably leaking exhaust. And if its leaking exhaust, you may die from carbon monoxide poisoning. So, fix the pipe.
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