NTK is a safe bet.

 

The upstream sensor is the master O2 sensor for A/F ratio input to the PCM and I would definitely recommend Mopar since it's still available from me at least.

The Mopar downstream sensors have been discontinued for some years now and I've used Denso without any issues.

 

I am running a MOPAR upstream O2 sensor and a DENSO downstream O2 sensor on my own 1998 4.0 ZJ.

After unsuccessfully locating a replacement Mopar downstream O2 sensor, I contacted Kolak and he recommended a Denso sensor, which I purchased from him. My CHECK ENGINE LIGHT turned off and it seems to be working good.

 

An order from Kolak is a wise idea. Otherwise I've had luck with Denso and NTK product lines

 

I’ve had zero problems with Denso O2s.

 

NTK or Denso are my go-to sensors these days. Bosch stuff isn't what it used to be, it seems.

 

I spent a while researching the NTK ones tonight. Looks like earlier this year they superceded earlier versions with a newer part. Their website says its the same sensor for both upstream and downstream, and I saw that it also works for YJs, XJs and a few other vehicles on a different forum which leads me to believe it doesn't come with a connector. I couldn't find any pictures of the part to verify one way or the other though. So not sure if that's a very viable option right now.

On RockAuto I saw some Walker brand ones that looked promising, anyone have experience with those?

All that to say that I will be going through Kolak to get what I need. Any further input would still be good though so people can reference this discussion in the future.

 

I have NTKs from Rock in three different ZJs and they are all good. I keep a spare set in reserve.

 

Doesnt look like RA has the NTK sensors.

 

As others have told you, you can use NTKs, which were the suppliers of the sensors on our ZJs

 

Denso > NTK > Bosch IMO.
I just replaced an NTK with a Denso on my '95 V8. The Denso is bigger and seems better made.