coolwind57

Ok fellas, I'm new. Just bought a 98 Cherokee with the 4.0L engine.

It was a nice surprise to find that a previous owner had put on a header. It also appears to have a new cat and muffler. Only problem is that the wire for the rear O2 sensor is just hanging there. The new parts have no port for the O2 sensor. ...and of course the check engine light is on.

So what do you guys think? Is the lack of that rear O2 sensor hurting anything? I understand that they may effect fuel economy. I just conducted my first test on economy and I'd gotten 17 mpg. I didn't think that was too bad.

The engine purrs right along, so I don't detect any rough or erratic idling or drivablilty.

Should I look at drilling and tapping a hole for a new rear sensor, or would you leave well enough alone? Where exactly does the sensor go, before or after the cat? This thing isn't suppose to have a cat that has an O2 port as an intergral part of it does it?

I wonder if I were to tap a hole, how far should the tip of the sensor fit inside the interior of the pipe. Wonder if it matters as long as its stuck in the exhaust stream....

What would you guys do?

KennyG

Summit Racing sells the little weld on bungs for the O2 sensors. I'd just (or have a competent muffler shop) drill a half inch hole in the pipe behind the convertor, and weld a bung on. That'll ensure the proper depth for the sensor. Personally, I don't think the rear sensor will cause drivability concerns, but the check engine light is the only way the computer can let you know of a problem, so if it's on all the time.... well, you get the idea.

Topjimmyk

Yess you should. i have a 98 cherokee and i ripped the wires out of the rear sensor some how. probably wheeling. and it idles real rough and sometimes and u can smell it burning rich if out stand out side. so id do it, but i have yet to replace mine so idk if thats the single cause of it not idling good. but it probably is. aka i didn't start idling rough until i a noticed the wires hanging there.

coolwind57

ok, thanks guys.

So just to confirm, the O2 goes just after the cat, right?

superj

take it to an exhaust shop and they'll put the bung on for 20 bucks or so. they'll even have hte bung in stock

k2keith

So just to confirm, the O2 goes just after the cat, right?

correct

coolwind57

Good to go, fellas. Its a done deal. Thanks for your help.

djb383

The second O2 sensor (after the cat) has no effect on engine performance, it only monitors cat performance. U can plug the O2 sensor into the factory harness and it will turn off the CEL. The O2 sensor is heated and gets very hot....be very careful where u hang the O2, if u don't screw it into the cat.