O2-sensor diagnostics

[Royy]

Last week P0430 popped up (Catalyst System Efficiency Below Threshold Bank 2). Around the same time P2096 (Post Catalyst Fuel Trim System Too Lean Bank 1) occasionally started appearing, but this one would disappear on its own after a couple of miles.

In November of last year I replaced the cats and Y-pipe with a complete assembly from Eastern Catalytic. I have put about 12,000 miles on it since then. O2-sensors were (allegedly) replaced last summer, before I bought the Jeep.

I'm hoping the cats aren't actually bad again, so I've been using the O2-sensor data to try to figure out what's going on... and it's got me at a loss.

I replaced the downstream sensors today, with brand new NTK ones. I wanted to do the upstream ones as well, but I couldn't reach the connector on the driver's side, and the sensor on the passenger side appears to be cross threaded... :favorites68:. I didn't have time to deal with that today, so I'll give that another try later.

These are some screenshots of the O2-sensor readings, taken after replacing the downstream sensors:

Screenshot 1 (75mph on the interstate)

You must be registered for see images attach

Screenshot 2 (75mph on the interstate)

You must be registered for see images attach

Screenshot 3 (bank 1 at idle)

You must be registered for see images attach

Screenshot 4 (bank 2 at idle)

You must be registered for see images attach

https://imgbb.com/

Screenshot 1 & 2 were both taken on the interstate, going around 75mph with cruise control on.
In screenshot 1 B2S1 looks way off to me, it doesn't seem to be properly switching. The other 3 sensors are fine, as far as I can tell.
In screenshot 2 B2S1 and B2S2 suddenly move around a lot more, even though driving conditions didn't change.

Screenshots 3 & 4 were taken at idle, with the engine at operating temperature. Increasing RPMs did not change the waves.
B1S1 seems to be working perfectly fine, but B1S2 (the brand new NTK sensor) on the other hand... or is this normal at idle?
For bank 2 both sensors seem to give weird readings, which I suppose could point to S2B1 being bad.

After this drive, I also had three pending codes in the system. P0430 was back, but I also got P2098 (Post Catalyst Fuel Trim System Too Lean Bank 2, which wasn't there before I put in the new sensor), and P0138 (O2 Sensor Circuit High Voltage Bank 1 Sensor 2, for the brand new sensor).


I have no visible exhaust or vacuum leaks, no noticeable symptoms of anything being wrong, and all fuel trim levels are perfectly fine (within the +/-4% range).

Besides B2S1 being bad, does anyone have any idea what else might be going on here?

 

[tjkj2002]

I'd say the cats are bad and B2S1 O2 is bad,remember non-OE cats are only 33%-66% efficient as OE cats,hence the high cost for OE cats(and OE manufacturer cat's sold as aftermarket under respective names).

Both downstream(sensor 2) O2's should hover in the 0.3(rich)-0.7(lean) volt range and not "switch" very fast,can spike up/down upon acceleration/deceleration but overall should stay in that range.

Both upstream(sensor 1) O2's should "switch" from 0.1(rich)-0.9(lean) volts very fast,also can spike up/down upon acceleration/deceleration but go right back to that fast switching.

 

[Royy]

Thanks, that's what I was afraid of
Dropping $1000+ on a new OE assembly won't be an option anytime soon I'm afraid.
And of course this happens when I'm about the take the Jeep on a drive across the country...

If I can get the B2S1 sensor replaced, do you think it would be safe to drive it for a while? There's no rattling sound or anything inside the cats, so there doesn't seem to be any loose material that could obstruct the exhaust.

 

[GunnerSchenck]

I'd say the same.. bad o2 sensor.. then if it was running too lean, it likely made your catalyst junk with all the unburnt fuel.. one caused the other.
You can drive it with just an 02 sensor replacement, but it's not going to have correct airflow and too much backpressure...bog down your engine, get worse mileage, accelerate and decelerate even worse.. cuse sporadic readings.. lack power uphill..
I'd replace the cats too.. but if you're not able yet and are going to drive it... get up to 65 (with nobody in sight either direction) and decelerate fairly quickly... might blow a little bit through the cats if its all recent..

 

[Royy]

That's one thing that confuses me though. The O2-codes indicate it's running lean, but all the fuel trim levels look great.

 

[HoosierJeeper]

My KL Cherokee had a cross threaded O2 sensor and it caused some lean code...could find it in the paper work if you wanted. Ended up getting most of the exhaust system replaced under warranty.

 

[adamkrz]

I had the same code a few months ago and ended up just replacing the upstream 02's thinking it was a lazy sensor - I didn't have a fancy code reader though.

The connectors were attached to the body and easy to unhook as were the sensors - both were original with almost 200k on the odometer, so far no more codes and It looks like my gas mileage may have improved.

 

[Royy]

I managed to remove the cross threaded sensor, but it ruined the threads inside the pipe. So I had to remove the exhaust assembly. Tomorrow I'm going to see if there's a place in town that'll weld in a new O2-bung.

While removing the exhaust assembly, I ran into some more surprises. The '05 has a different exhaust manifold than earlier KJ's. It doesn't use the V-clamp. Instead the manifold and the exhaust downpipe have bigger flanges, which are bolted together.

Turns out that the place that installed my cats (and cross threaded the O2 sensor) also cross threaded 3 of the 4 bolts for the flanges... Luckily they apparently used cheap bolts, because I was able to just twist them apart. Good thing, because it would have been impossible to get a saw up there to cut them. They also didn't use the gaskets, which I did give to them.

The irony here is that when I bought my new cats, I didn't know the '05 has a different exhaust manifold. I didn't want to have to deal with the V-clamp after all the horror stories I read on here about it, and that was one of the reasons why I decided not to install the cats myself... :Insane:

 

[adamkrz]

I managed to remove the cross threaded sensor, but it ruined the threads inside the pipe. So I had to remove the exhaust assembly. Tomorrow I'm going to see if there's a place in town that'll weld in a new O2-bung.

While removing the exhaust assembly, I ran into some more surprises. The '05 has a different exhaust manifold than earlier KJ's. It doesn't use the V-clamp. Instead the manifold and the exhaust downpipe have bigger flanges, which are bolted together.

Turns out that the place that installed my cats (and cross threaded the O2 sensor) also cross threaded 3 of the 4 bolts for the flanges... Luckily they apparently used cheap bolts, because I was able to just twist them apart. Good thing, because it would have been impossible to get a saw up there to cut them. They also didn't use the gaskets, which I did give to them.

The irony here is that when I bought my new cats, I didn't know the '05 has a different exhaust manifold. I didn't want to have to deal with the V-clamp after all the horror stories I read on here about it, and that was one of the reasons why I decided not to install the cats myself... :Insane:

There are so many hack shops out there, I had some steering rack bushings installed a few weeks back along with an alignment and after that my jeep was barely drive able -plus they removed my oil drip tray and threw it out.

 

[GunnerSchenck]

There are so many hack shops out there.

X2.

Last time I paid someone to work on my car was 3 years ago I had a shop put my cats on an 03 taurus.. one of those, I just don't wanna do it kinda jobs.. so I paid them to.
They crossthreaded and then broke off the bolt that held the cat's flange to the exhaust manifold. So rather than drill it out, they decided just to weld the two together... charged me 40% markup, kept my old cats (all 3) and 300 in labor. To mess up the job...

Needless to say, nobody but me has touched my vehicles since.. I could've done that job, but just didn't feel like it lol.. so laziness cost me 850 and I didn't even get my old cats back..
Moral of the story, don't be lazy if you can do it.. just do it, and do it right.

 

[renegade 04]

If the o2 sensor bung was cross threaded you should be able to run a tap in side of the hole to clean it up thats what I did.

 

[Royy]

If the o2 sensor bung was cross threaded you should be able to run a tap in side of the hole to clean it up thats what I did.

I read on some other forums of people having done that, and then their sensors still didn't seal properly. I guess it probably would have worked, but I just didn't have time to try a bunch of different things.


Got the new bung welded in, and everything put together again. I drove a couple miles in town, and no pending codes so far.