02 Sensor Question

[98XJSport]

I have a 98 xj 4.0, with what I think is a lazy upstream O2 sensor. My question, since Im away from my jeep until tomorrow, is it possible to hook up the downstream O2 sensor in place of the upstream? This will let me test to see if that's my problem. Plus much cheaper than buying one and hoping it fixes the problem. Thanks.

[Creech]

Probably. I don't think there's any real difference in the two. try it and let us know how it works. I'm assuming you're hoping that by switching the two, you'll get the code for the downstream sensor instead of the upstream.

[langer1]

If the down stream is also bad, what would prove?

[qwerty247]

also what makes you think that its lazy?

the downstream sensor has a much longer lead

[98XJSport]

Ok my problem is that the jeep is running poorly, starting up to a minute after startup, lasting for a few minutes, then running ok, but with poor fuel mileage. I know it's not the downstream, and Ive replaced most other sensors that could have an effect on fuel delivery. Next logical step is the upstream O2. Instead of buying one I would rather try one and see if it fixes my problem, then buy one if need be. As Im away from my jeep until at least tomorrow, I thought Id ask on here, since go try it isn't an option.

[90xj06]

the o2 sensors dont come online untill warm up. try pulling codes.

[98XJSport]

The only thing it will give me is pending code for catalyst, O2 sensor circuit, O2 sensor Heater. Which I know isn't my downstream sensor. Which leaves....

[Saudade]

The Jeep Parts manual shows different pigtail lengths for the 2. AutoZone shows the same OEM number for both. Seems like, as long as the connector will reach, you can swap them.

[langer1]

I guess then you need to use an Ohm meter and test the heater in the o2 sensor and test for the proper voltage to the heater.
Universal replacment o2 sensors are the same for up and down stream, but thats because they don't come with wires, us reuse your old wire and plug.
Also there is a relay in the PDC for both sensors which could also be the problem.

[98XJSport]

So the sensors are the same, its simply the wire length. I kinda suspected such. I will try it tomorrow and verify.

[langer1]

So the sensors are the same, its simply the wire length. I kinda suspected such. I will try it tomorrow and verify.
Don't forget the relays

[Fish'nCarz]

Don't forget the relays
How can you test the relays? (I couldn't find it with search)

[98XJSport]

Easiest way is swapping it with another like relay if its not soldered in, Ive never looked. Will be something I will check if a quick sensor swap won't help.

[qwerty247]

do you know which relay it is that controls the O2 sensor?

[langer1]

do you know which relay it is that controls the O2 sensor?
That depends on the year.

[qwerty247]

97 4.0

thought i would check them now you mention it.
are these common to fail ?

thanks