bad cat or possibly O2 sensor?

[gCracker]

So after talking to Mike at the meeting tonight I am starting to wonder if I really need to replace my cat or just the Oxygen sensor.

Symptoms:
1.) cold motor stumbles and coughs under load until it is warmed up
2.) start the motor, let it idle, about 1 minute later it will stumble and almost stall and then will be fine.
3.) no check engine light, I also just tried to get it to display the error codes(on-offx3 method and od reset button method) but did not get any error codes displayed

The PO said it was the cat so I ordered one and am planning to install it next week, but if I can just replace the 02 sensor(s) that would be better.

Thoughts?

[MrMindless]

shoulda pulled codes with a reader at the meeting.

something I didn\'t think of then is that it\'s misbehaving when it\'s cold.  fuel trim should not be effected by the O2 when in closed loop (until coolant reaches ~170˚)

[MrMindless]

I don\'t know about TJs, but Dakotas were a bastard year in 1998 - key cycles do nothing and cluster check does not display codes: only a reader will get them for you.  either a bad O2 or a bad catalytic *should* set a code that will trip the MIL.

[Guest]

I suck with Fuel Injection.....But..... Id think the Cat would be more of an issue when hot..........Id look for a cracked vacuum line....Ive had a couple cars in the past with old rubber lines.....During the summer the lines get real warm and the cracks spread open..........

[gCracker]

Yeah I realized I should have asked Dopple to read for codes while at the meeting and 98 TJ\'s are also hit and miss on weather or not they will display the codes without a reader.  

Man I hate working in Victor.. no auto parts stores to stop at to have the codes read.


hmm.. still scratching my head on what to try first.

[MrMindless]

gCracker wrote:
Yeah I realized I should have asked Dopple to read for codes while at the meeting.

And what am I? A wet sock? :-)
(I can pull codes too...)

[gCracker]

oh, I did not realize you had a code reader. sorry.  Maybe we can meet up some time.

[Guest]

I would deffinitly check the codes before replacing.  However, you cant go wrong with a new caty.  

PS I would have stayed to check out your junk yesterday but I thought you were coming to the Gathering.

[Guest]

If you replace the cat don\'t leave it at the curb scrap yards are paying good $$ for them, $70.00 for the big GM\'s. Just for the inners you can get $10. per lbs.

[Guest]

I dont know if this helps but my bank 2... 02 sensor went bad about 2 months after i put the new exhaust on the xj despite the check engine like there was nasty carbon actually around the the outside of the exhaust pipe going back toward the truck 3/4 of an inch

[Guest]

ya\' know, a basic code reader is only $60 at Wal-Mart (and it\'s a much better one than the one I spent $160 on three years ago).

[gCracker]

I am pretty set on the conclusion that it is the front O2 sensor, which i now have a replacement for, but I could not get the old one out when I had a chance to work on it.  I am still going to replace the cat as it rattles so it will all be done at once when i get a chance.  I still just let the Jeep run for a couple minutes when it is cold and it is fine.