hello today was trying to replace o2 sensor picked up one from auto zone but started to work on what we thought and could be the o2 Senor but were just wanting to make sure if there are two o2 senors a downstream and upstream or is it only one?? Also tips or tricks to get it out without breaking it?

As far as I know there should be only one O2 sensor on a 1991 model. The dual-sensor setup would have come in with OBD-II diagnostics in 1996.

As long as you're sure it's going to be replaced, cut the wire flush and use a six-point deep socket with the exhaust system hot. It's best to wear protective leather gloves to protect your hands while working around a hot exhaust system - I have the scars to prove it.

Thanks you very much for replying and helping me out. It was very helpful and now we know something new and helpful trick to get it out thanks again

Heat is your friend. Either use a torch on the exhaust pipe where the sensor mounts (not on the sensor itself), or run the car long enough to get the exhaust system good and hot.

The sensor will come out much more easily.

Do NOT try to get that thing out with an open end wrench!