TJ O2 Sensors and/or Cat Converter

[kodyharrell]

Either my o2 sensors are goin out, or my cat is getting clogged. It is sluggish sometimes but not often. (Kinda like it was in a thread I made a few months ago)
But I THINK it's one or the other. I cleaned the o2 sensors with a wire brush today, and reset the code, but as I started to pull off, it still kinda sputtered. At speed it is fine. In 4wd it is fine. I'm sorta hoping that it's just an o2 sensor. But anyways, o2 sensors or cat converter...

[wyleone]

You can't clean O2 sensors with a wire brush.....
It is not uncommon for the o2 to fail on a TJ, I have replaced many of them.

[kodyharrell]

Yeah I'm pretty sure that's what it is. But hate to buy a new one and it be something else. Then I cant get my money back on the sensor.

[fin]

if it your cat it would be glowing red after driving souunds like o2 sensor or dirty mas airflow sensor

[wyleone]

Originally Posted by fin

if it your cat it would be glowing red after driving .....

Not necessarily. I replace many on different vehicles with no overheating. Glowing red cats usually indicate a major lean out. A bad O2 can do this and kill a catalytic converter quick, by being rich biased.

If you do not want to buy an O2 on just a code, I don't blame you. An O2 code can be set by other things....like a bad MAF. But you will need someone to use a scan tool to inspect the data stream and make a diagnosis cheaply or free. If not, it will cost you diagnosis and an o2.

No one will be able to call it for sure on this, or any other board. We can only speculate on info you provide.

[kodyharrell]

Yeah. From what I'm researching it doesn't look like tj's have MAF's..
I got a thing from autozone when they hooked up the scanner and it says:

Troubleshooting PO171
Definition
Fuel trim bank one condition explanation:
The powertrain control module uses the oxygen sensor to calculate the Air/Fuel ratio of the engine. The computer has recognized a rich or lean condition on one bank only.
Probable Cause
1.If bank one and two codes set together suspect fuel pressure or MAF
2.Oxygen sensor defective
3.Ignition misfire-repair
4.Fuel injector problem


Troubleshooting PO420
Definition
Catalyst efficiency low-bank 1
Explanation
The oxygen sensors monitor the catalytic converters ability to store oxygen.
Probable Cause
1.Catalytic converter defective (failure possibly due to # 2,3, or 4)
2.Engine misfire or running condition
3.large vacuum leak
4.Engine oil leakage into exhaust-valve guide seals, piston rings

I dont really know if that would help any, but that's on the paper they printed out from their scanner of possible problems...

[wyleone]

Well, the P0171 is a lean code. You have only one bank as it is an inline motor. This can be caused by a vacuum leak. Typical. Intake gaskets leak on 4.0Ls (as well as exhaust), the injector o rings leak at the bottom of the injectors, etc
This will also give an erratic idle. But not so much of the hesitation you described.

Oh yes, You are correct, 4.0Ls do not have MAFs. I was just using that as an example.

Autozone uses a generic OBDII scan tool that does fancy stuff that they usually cannot elaborate on.

The big question, is the Jeep running rich at the time you are getting the bog/hesitation? Black smoke out the tailpipe?

[kodyharrell]

I never noticed black smoke, but havent really paid that much attention.

it didnt affect my gas mileage today much if any.

[kodyharrell]

Messed around a few minutes ago, and unplugged the o2 sensor to see how it runs (heard that it's a good way to tell if it's the sensor) and it ran worse than when the o2 was plugged in, so I got underneath while it was running for some reason, and kinda heard a 'airy' sound, so started feeling for a leak, and sure enough, after the upstream o2 sensor, there is a 1" crack that's not very wide, MAYBE the width of a penny at it's widest. Then there is one that is surely the width of a penny where the exhaust and cat converter meet, like someone cut it with a buckeye and left the hole. It's about 2" long.. Held my hand over end of exhaust and could hold up the exhaust flow. The cracks are apparently big enough to let all the exhaust out. Gonna get them welded up tomorrow and hope that does the trick..