So, like a true idiot, i got my new NTK o2 senors (upstream and downstream) and immediately took them out of the boxes for inspection. My problem is... I cant figure out which one came out of which box (idiot, i know lol) so here is a pic and maybe someone can tell me.
Another thing is... just for giggles i pulled the downstream and tried to thread the new one in, and it doesnt seem to want to go more than about 3/4 of a turn. My XJ is EXTREMELY rusty, so i was thing that the threads are just full of trash? Correct me if im wrong. Thanks Yall!

 

Compare the wire lead lengths to the ones you took out. The one farthest away from where you plug it in probably has the longest lead. Or see if there is a number stamped on the sensor and check the web site of the place you bought them.

 

Bought them from rockauto.com and i have looked for a part number on the sensors but nothing... I am fairly certain that the lead lengths are the same on the both of them.

 

looks like the tips are different, could look into that

 

Yes sir, and i have done some looking and cant seem to figure out which is which. I know that alot of people on this forum use NTK sensors... someone should know. Wish i could find it but the search brings up nothing useful in this case.

 

The upstream one I bought last month (23151 I believe) is the one on the right. Can't verify in that shot but I think there's a total of 4 or 5 of those small round holes. Definitely not the thing on the left, though. However, the wires out of mine weren't twisted like that.

Oh, and although I bought a new one it wasn't me who actually replaced it. I couldn't get my old one off in the driveway, took it to a mechanic I know and he had to heat it up literally glowing hot before it came out.

 

I'm pretty sure the wires for the upstream O2 are longer than the downstream?

 

The one picture on the left is NTK 23099. The one on the right is 23151. I have them sitting in front of me. I got them for my 99 xj 4.0.

Use a thread chaser to clean up the threads (18mm x 1.5) (I think).......

 

upstream is on the right
downstream is on the left

I just did mine yesterday and got them from rockauto too... did you use the discount code to get your 5% off??

if anyone need a code let me know I have one good till June 17th and can be used multiple times.

 

Thanks everyone! I did finally get them in and, volla! It runs like a champ! The CEL went off right after i put them in and disconnected the battery for a few minutes, but now it is back on. Ive only driven it about 25 miles so far and i have heard that 60 miles is a full cycle? Can i go to the parts house and have them clear the codes it was throwing?

 

Yes you sure can go get the codes cleared now. And they shouldn't come back. Glad you got it figured out

 

Thank you sir!