does my 91 honda civic base model hatchback have one or two o2 sensors?

Usually there are two sensors. The first one is upstream of the converter. It is called bank one, sensor one. The first sensor provides feedback to the fuel trim to adjust the mixture. The second sensor is down stream of the converter and it called bank one, sensor two. It tells you if he catalytic converter is working in most cars. -- In some cars the second sensor is used in fuel trim too.

I have the one up in my header but I cant figure out where the plug is at for the second sensor to plug into

If you have a second sensor, it would be after the catalytic converter. Check with other owners on a Honda forum. You may have only one sensor or someone removed the cat and sensor. Do you have a check engine light?

Yeah it comes on after driving for a while the person I bought the car from home made the header and exhaust so the eliminated the cat and everything but I have a new header and I bought a brand new exhaust and cat for it now I just gotta find the plug so I can plug the second sensor in if there is a second sensor on it

click the image it might help

That did help some, I just hope they didnt cut the plug off or anything, thanks for the help man I appreciate it.

you have a 91 it only has the one on the upper portion of the header trust me you wont find one on the cat they didnt do that till like 2002 i do believe

or around there

Alright sweet thanks man

88-91 d15b only have the ox sensor in the exhaust manifold.