Every catalytic converter thread I find shows all these symptoms happening before ultimately replacing the cats. In my case these symptoms only arrived after replacing the cats and O2 sensors


Some background information. Recently I had thrown a CEL for P0158 - O2 Sensor 2/2 Circut High and coupled with the CEL I had a loud clanging noise coming from the Cat at low speed acceleration so I obviously had a bad catalytic converter. In this condition the Jeep ran fine, idle was smooth, never overheated, acceleration wasn't an issue. If I cleared the codes it generally would take a week or two to return. So I went ahead and replaced the catalytic converters as well as all (4) O2 sensors since I'm just over 200k miles on the clock. I went through the catalytic converter break in process and cleared my CEL codes. I noticed fairly quickly after replacement the idle seemed to be a little more choppy than usual.


After a short time the idle got worse and my CEL came back. The Jeep began overheating at idle (around 3/4 up the gauge instead of only about halfway). The new cats never physically looked like they were getting hot, no glowing red or anything like that. And now the idle is really rough and the CEL codes are misfire codes. Acceleration is garbage and the throttle hesitates. I did swap in the Amazon O2 sensors which I've read have given some JK owners issues so I took all of my old O2 sensors and put them back in. Figuring that since the cat was clanging loudly the original O2 sensors were probably still fine. This changed nothing. Current CEL codes are P0300 - Multiple Cylinder Misfire; P0158 - O2 Sensor 2/2 Circut High; P0135 - O2 Sensor 1/1 Heater Performance


So in it's current condition it's exhibiting all the signs of a clogged catalytic converter but the cats are brand new. I know this doesn't necessarily mean the cats aren't clogged right out of the box or the break-in actually clogged them but I hesitate to come to that conclusion. Is it possible that something happened with the PCM or anything else while I was in there wrenching out the old exhaust? Threw the computer for a loop when I used the less-than-reputable O2 sensors? I only replaced the section from the manifold collars to the Y-Pipe. I used my AEV ProCal to erase the codes. At least the exhaust clanging stopped.


Does anyone have any sage advice before I begin the arduous task of ripping it apart again? That kicked my butt the first time


Thanks in advance for my first post here!


2008 Jeep Wrangler Unlimited Sahara 3.8L/Auto

 

Welcome to JKF.. A question... what is the exhaust Flow out the tail pipe? I have read on forums of a ground wire issue in the injectors wiring causing misfire code and poor performance. Check the pins in the connectors one might have pushed back. Good group here so hopefully someone has more suggestions. Good Luck.. If you pull the Cats, check how it runs w/out any exhaust connected to the manifold cold engine should be Closed Loop on the computer till it warms up.

 

As far as exhaust flow I don't know of any official way to test it but it's coming out of the tailpipe as usual with good strength like I would expect, just very choppy because of the misfire. In addition I noticed the exhaust smells very rich

I went ahead a pulled the O2 sensors and reinstalled the new ones. I did have a little issue with the 1/1 plug when I initially replaced them so the pin thing made sense to check. All the pins are fine, O2 sensors are getting voltage.

Now the Jeep is throwing:

P0300 - Multiple Cylinder Misfire
P0138 - O2 Sensor 1/2 Circuit High
P0158 - O2 Sensor 2/2 Circuit High

It seems like the O2 sensor codes are jumping around on me.

I am focused on the cats and O2 sensors because that is the only thing that has changed from then until now, but it has been raining like crazy lately so it is possible that I have a coincidental, unrelated issue that has come up like a loose connector getting water or ground corroding or something, but I kind of doubt it.

 

To update this, the throttle body pretty built up, found a corroded post on the igniton coil, and two of my 6 spark plugs have seen better days.

- Cleaned throttle body
- Replaced ignition coil
- Replaced all plugs and wires
- Scoped cylinders
- Repaired unrelated coolant leak at thermostat housing
- Ran a cycle of fuel cleaner through

The Jeep is running much better, and the misfire codes are gone, though I am still getting O2 sensor codes. I am either going to order a new set or install the old set again and keep working on that. No overheating, doesn't smell rich anymore.

So as I continue to troubleshoot this, does anybody have a plausible explanation as to why these things that were present prior to my cat swap were not causing any sort of issue or showing any symptoms, and they all began after the new cats and O2 sensors were installed? This all came up within a week of install, but the corrosion and buildup and faulty plugs have been there for a while now. But prior to the cats there was zero sign of issue.

 

From the first post:
Maybe the old cats were not actually bad and the noise was from something else like a loose exhaust and a rough running engine ??? P0158 doesn't indicate bad cats, and bad cats are not listed in the manual as a possible cause.

 

I suppose I forgot to update this thread for anyone elses benefit. The problem ended up being the new cats. The upper honeycomb I can see through the input side looks fine but something must be going on internally. I replaced them again and everything is fine now. Brand new out of the box, go figure. Did the same break in procedure with this new set.