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highup

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Guess I will have to try to find someone to work on it. Neither OBD1 or OBD2 work on a '95 Lumina. Jumper doesn't work either. :(

Has the O2 sensor ever been replaced while you have owned the vehicle?
They don't last forever, and if they stop working, the engine will run rich because the computer isn't getting any feedback from the sensor.
You said it runs good when really cold outside? ...........a rich condition caused by a failed O2 sensor might act as a choke would on a carbureted car when it is cold. Running rich when hot could cause stumbling, especially at low RPMs.
If the mileage is crappy, that too is a sign of a failed O2 sensor. I have never checked for how to test one, but it's worth looking into. Possibly all that is needed is an OHM meter. I think yours would most likely be a 3 wire, heated O2 sensor. My '83 4.3 v6 had a two wire unheated sensor, so I replaced it with a three wire heated one. My mileage went up over 4mpg.
 
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highup

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It screws into either the lower part of the exhaust manifold, or near the beginnings of the exhaust pipe just below the exhaust manifold near where the right an left exhaust pipes come together.
 

Ernesto

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I replaced the O2 sensor on my old dodge when I was having a problem with it running rich and zero power, plus a few other small items. Finally took it to my mechanic, turned out to be the CAT. Now it runs as good as it ever has and actually sounds like a V8. Has 140,000 on a 5.9liter, 1997 dodge Ram PU
 

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