O2 sensor problems

[Khost26]

Hi. I have searched not only here but all over the web to see if i can make sense of this but i haven't been able to.
I have a s13 blacktop sr in my car. I went to do emissions with the car and failed 2 times. In Colorado if you fail you get a free check to see why your car is failing and when i did this, they told me that my o2 sensor wasn't allowing my car to run closed loop and that the 02 was bad. Well i got a 87 300zx turbo one from advanced and it didn't fix anything, so i returned it. I cleaned the old one and put it back in and let it warm up and then checked the voltage at the pig tail of the sr 02. It was very low but when i gave it gas it did go up. I do know i am running very rich. My CO during emissions was 87 and the limit is 20. My mileage is about 13 (somewhat of a heavy foot. ) But i really need help with this. Is there anyway for me to tell if it is the o2? Or if it is something different. When i unplug the o2 the cars idle doesn't change or if it does not enough to tell and i don't have a tachometer to verify. Please!! Any help would be a life savor.

[Khost26]

Anyone? I really cant figure this out.

[Second Shadow]

if you're getting 13 mpg then running that rich sounds like it's not the O2 sensor. they don't do THAT much, I would suspect the MAF, coolant temp sensor, leaky injectors, or timing. if those are all good there are some other things that can make you run rich but those are the most common.

there are several articles explaining how to check these, most can be done with a multimeter, and what your looking for is proper voltages/grounds/resistances on their respective wires.

[Khost26]

if you're getting 13 mpg then running that rich sounds like it's not the O2 sensor. they don't do THAT much, I would suspect the MAF, coolant temp sensor, leaky injectors, or timing. if those are all good there are some other things that can make you run rich but those are the most common.

there are several articles explaining how to check these, most can be done with a multimeter, and what your looking for is proper voltages/grounds/resistances on their respective wires.

Well I'm pretty sure that the MAF is fine. But my temp gauge did recently stop working so maybe that could be part of it. Thank you. Ill see if i can check those other things.