problem with o2 sensors

This all started with a blown cat, a buddy of mine welded in a new cat and replaced the downstream o2 as well. I did the battery reset to clear the check eng. light. All was good for about 3 days, the check eng. came back on and had autozone check the error, it was a bad o2, replaced it and reset, 2 days later same thing. So i've replaced the down stream o2 four times, and the upstream once, because oddly enough that one of the error checks said that both 02's were bad. Again ive got my check eng. light on and had it checked again at a different place and still says that, o2 sensor 1 in bank 1 is bad. Im stumped and need any help that can be given.:banghead::banghead::helpme:

dodgy downstream/upstream o2 relay?

You shouldn't throw parts at a problem like this... O2 sensors don't go bad that fast! Hope they were free warranty replacements

I would bet on a sensor power bus or sensor ground issue. What year is yours? Where the O2 sensor grounds are, and how they are powered, depends on the year.

EDIT: RoadHog's relay idea is another good one, they are definitely suspect. Try swapping relays around (write letters on top of them so you can put them back where they were in the first place afterwards.) If you swap the one that feeds the O2 sensors into the fuel pump relay socket and the fuel pump stops working... you have your culprit.

kastein has a good point about it being a ground/bus problem. Could you have damaged or displaced the wiring removing or replacing the exhaust?
Or a really way out one - any chance the welding damaged the bungs where the o2 sensors fit in? (had a guy on the Porsche boards have this happen and it leaked causing inconsistent readings - looked like bad sensors/wiring)

they were all warranted, the xj is an 98 sport 4dr. 4.0L 4wheel drive

checked for the o2 sensor relays, and could not find any, did find a 15a fuse that was blown, and the other problem with this is that I have no idea what this fuse did. Its one of the mini blades, in the fuse block and under the cover all it says is that its supposed to be a 15a fuse???

Post a picture up.


So why did your cat go bad to begin with???

Hmmmm

One of those relays is the oxygen heater relay for the o2 sensor. Find it, test it.

check your owners manual/fsm and check what he fuse is.

Posting the exact code number(s) will yield the most accurate responses. There are a number of codes for oxygen sensors and the root causes of the different numbers can vary.

Yup, no more sensor replacements. You definitely have something else going on!

Relay, fuse, wiring, connectors, etc.

I'd sure start with that blown fuse. Pretty sure the oxygen sensor heater circuit fuse is a 15 amp in the power distribution center.