cornhusker85

Can not running a down stream o2 sensor cause the jeep to run bad? My understanding was that the downstream o2 sensor just told the computer if your cat was bad.

OEJ

you are correct. i just went through this. when my down stream o2 went it was just a cel and crappy gas milage. about a month later my upstream went and i was dead in the water. it would start then stall. i could have drove it but whenever i stopped at a light,etc, i would have to put in N and keep the rpms up. so my addvise is if you have the money do them both. also keep in mind that it is a poss that ur catis goin bad,since thats why that o2 is there; wich you know.

its one of those " while your at it... things". In my case my front o2 was so baddly rounded and rust welded inthe bung, that i just said the hell with it and bout a new down pipe from walker. igot a discount and only paid 40. bucks for it. well worth the time savings. i had the old 1 out and new 1 installed in less than 1-1/2 hrs.
just an fyi. good luck.

Fraser

Yes, especially on a 97+. not having it will cause the computer to run in limp mode, causing lack of power and horrible gas mileage

gmv93

it may cause horrible milage on some cars because it is trying to make mixture rich and it tries to cool engine by consuming gasoline as internal coolant, and it tries to reduce emmissions.

actually post o2 sensors has no effect on mixture control. it is there to check if cat is ok or not.

jomps

but if the post sensor is bad then your pre wont work because they bounce off eachother..replace them together

OEJ

Not true. They are not even linked to the same cpu port. Dwn stream only sences the condition of the cat. Up stream handles air, fuel mixtures and noxious mixtures. Then the cpu makes corrections.

On a diff note. I learned something new todaay. After market 02's. Are not reccomended for chrysler dodge or jeeps. I installed a new bosch 2 weeks ago and it is bad allready. Went to the dealer and got a mopar o2 and the bulb and sensor itself are whorlds apart from the after market ones.

So note to self do not buy anything but mopar 02's you will be changing it out. The machanic verified all this.

Gee oh Dee

and no effect on how our XJs run period.

Wrong. Completely.
Yep. Lots have posted issues they have had with them.

jomps

I stand corrected...was going off information in the thread o2 sensor operation fyi...

Gee oh Dee

Yeah, quite a few BS answers get tossed around about a few topics because LOTS of people THINK they know what they are talking about, but really don't.

Then people trying to learn stumble across conflicting info, and the issues start to snowball.

OEJ

We'll said. Put about 60 miles on her taday and max air. Runnin sweet. Nock on wood.lol.

djb383

......and as long as the downstream is electrically connected to the wiring harness, shouldn't have a CEL.

OEJ

You are absolutely correct. That's what mine did. She died right in the driveway when I got rea dy to leave for work. I'm glad and lucky she died in the drive ay twice in 2 wks.lol.

jomps

thanks for clearing that up then

OEJ

Oh. To the op sorry for jacking ur thread bro.

cornhusker85

No worries.