I purchased a project Cherokee. It needed a computer. I replaced it and it started and runs great except for this issue I'm writing about now. Ive actually dealt with this for over a year. It starts fine and idles fine for a few minutes. Then it runs rough and sometimes stalls. I let it run a few more minutes and then it runs perfect until shut off. Give it a couple minutes off and the rough miss returns and the process repeats. It throws a O2 sensor code. It is for a second sensor but there's only one. No wire or socket any where i find for a second one. The installed one is brand new. Is the computer the wrong one? I'm lost solving this one.
thanks

 

What year?

 

It is a 1998 4x4 4.0L

 

You should have one downstream from the CAT. If there isn't one someone apparently deleted it.

 

Sounds like someone hacked the harness. Should have an o2 sensor just below the exhaust manifold (upstream), and another just after the catalytic convertor (downstream). If the upstream is missing, check the injector harness for any cut wires. They may have been tucked into the harness and taped over. If the downstream is missing, check around the transfer case to see if it was taped or ziptied out of the way. Or cut. I think that harness runs along the top of the transmission, so check up there, too.

 

To confuse me more. The wiring diagram of the computer shows one O2.

 

what code?...there are a few O2 codes

that will tell you whether it is front or rear

In a '96, the post Cat O2 sensor has NO effect on engine running

I dont think it does in a '98 either, but always open to be proven wrong

 

It's only there to monitor cat efficiency and will set a code in OBDII. (96 or later)

 

Yep. There's a sticky on that. The info in it was taken from a 97 FSM. It didn't change until the sensors were multiplied. I forget which year that was.

 

I'll get the exact code. Hmmm. Well the O2 that is still there is post Catalytic. Hmmm. If that has no engine effect, if I could find cut wires maybe I could swap it onto the missing pre cat.

 

Assuming this is an american 1998 XJ you should have 2 o2 sensors and one cat just after the transmission cross member. The upstream 02 sensor is before the cat. The down stream is after the cat. If the cat is missing then repair the cut or damaged downstream wires. Have a bung welded into the exhaust and install the downstream o2 sensor. If you dont want to install a cat then install a defouler into the bung then the o2 sensor. This will be enough to trick the ECU.

And post some pics

 

vehicle will probably run poorly without a pre cat O2 sensor as it is critical sensor to PCM

You need to identify where the wires have been cut or unplugged, wire in a new O2 sensor, have an exhaust bloke weld a bung in into a pre-cat location

This should be close to where everyone else has theres fitted, as the front O2 sensor can play up if misplaced