Working on my 91 s10 Blazer, 4.3 4x4. Looking at Advance Auto's web site, they say I have two, an upstream and downstream.Downstream waseasy to get, down on the Y pipe. I assumed I could see the upstream sensor, in the manifold. When I went to remove it, I realized I had the wrong one, I think it is the coolant temp sensor over there, on the passengerside.

Sonow I'm not sure there is a secondo2 sensor, Haynes and Chilton only mention the one. So if there is only one, which should I put in there, upstream or downstream? I assume downstream, because it plug fits. But we can all see how fas assuming anything has got me. I appreciate any help you guys have to offer.
Thanks for checking me out.

 

Mine only has one. Crawl under it and look. There will be one for sure just before the cat converter on the right side just behind the right front wheel. It is a single wire. Run your hand along the rest of the exhaust pipe (when cold) all the way to the muffler. I bet you do not find one.

 

Of course I found that one, it is the one I referred to as 'downstream'. I am trying to determine if there is another o2 sensor on a 4.3 from 91. Thanks tho

 

Downstream means AFTER the cat converter. The only one you probably have and found is upstream.

 

Yep, the sensor you have found which is directly after the "Y" in the y-pipe and before the catalytic converter is the upstream sensor. If you do not have one behind the catalytic converter, then you only have one sensor.

 

Okay, that is great, I only have one o2 sensor to worry about. Thanks swartlkk