Yep, it sounds like they can be inefficient enough that the after cat O2 sensors see that and set DTC's.

 

MISFIRE IS GONE!
got the new cats late last thursday (who delivers at 8:30pm!?) and installed friday night/saturday morning. apparently this is a two person job. and apparently it should have been easier with jackstands. meh. got 'er all sorted out. new up and down o2 sensors on the drivers side, old new (post first engine, pre second engine) installed on passenger side. runs great. battery was frozen as well apparently, so got a new battery in there as well. runs fine. still a couple codes i'm going to start looking into. p0032/0052 upstream cat pre heat resistance high iirc. i've got some oddball electrical gremlins to sort out now too. interior lights don't turn on with doors getting in, and stereo doesn't turn off when i open the doors after shutting off. my post connectors are stock, and seriously beat up so i've ordered some new ones that accommodate a couple of accessories. i'll start there. maybe look over some grounds by the footwells which apparently can cause problems. i'm not driving the jeep daily yet, so i'm not stressed about the o2 codes. yet. i'll update when there are uhh updates.

 

 

Yep, "cats" == catalytic converters.

 

More Updates!
since getting 'er back up and running, i had a misfire cause my knock sensor harness was melted and it came loose, (fyi, replacement knock sensor harnesses are common with fuel pump harnesses off aaa uhh volvo? among other things), replaced the knock sensor cause i was there. i always had issues with the o2 sensors, bot pre and post, both banks. changed 'em all, doubled up my ground wire (similar situation another member had - that worked for him) but to no avail, ran with codes showing and eventually on a fall day going downtown (which is literally about 150' lower in the valley) i had another misfire. i parked the jeep for a bit and got a giant '96 suburban beater for a daily driver.
I sent my pcm back to flagship one to troubleshoot as sort of a hail mary cause i'd run out of ideas. it sort of got lost in the fray and they didn't end up running any diagnostics on the pcm to my knowledge, but they did send me a replacement pcm without hassle. Got the new PCM in annnnd NO CHECK ENGINE LIGHT! seriously... i've owned this jeep since 2010 and it's never had a clear dash. it looks naked. jeep is running pretty great now. i did have a leak on the click connect of the fuel like at the final bend, probabaly from over-use during two engine swaps, so i ordered a new piece (now one piece from tank to manifold - eliminating the leaky connection entirely) but will wait till it's not -35c to kick the wife's CRV (electric power steering freezes in the cold... seriously) out of the shop and replace my fuel line. I do have a passenger airbag light that never goes off, and suddenly my horn has stopped working. but my jeep works and i am happy. in retrospect, PCMs aren't nearly as expensive (rebuild was less that $400 with a lifetime warranty and programmed to my VIN, no stealership required) as a new engine. and sensors. and throttle body. and all four cats. learn from my lessons. hope everyone is having a pretty okay 2019.

 

So your saying bad cats was the cause of the 1, 3 & 5 misfires??? I'm having this issue in my 2012 JK and they can not figure it out. Misfires keep coming back. Only thing left to do is tear the motor apart.. is what they tell me..
PCM was replaced already too. ???

 

The misfires can be sticking fuel injectors. Does the engine idle rough when cold but smooth out when warmed up? Try some lucas fuel injector cleaner at double strength. The oil component lubricates the fuel injectors so they don't stick. If this is the issue you will have to replace the fuel injectors like I am about to do. I have to put a little Lucas in every tank until I get a chance to replace the injectors.

 

It's not the injectors. that was the first thing they checked.
Everything runs as it should until it sits at idle.. it could be idling for 20 minutes or 40 minutes.. for some unknown reason is misfires. Codes 300, 301, 303, 305.

This initially started with 02 sensors... then I chased codes to practically every sensor, even replacing the oil sending unit in the process.
My question about the cats was because this was my first thought after the codes continued..
One camshaft was replaced... but now we're at a standstill with no fix. It's a 2012 and I do not plan to get rid of it or consider junking it.

Any help in knowing what people had to replace or fix with this issue is appreciated.

 

I'm having the exact same issue. 2012 Jeep Unlimited 97k issues started happening around 94k


I left my jeep behind while deployed for 9 months (I had someone drive it every now and then, but I dot think they filled it up more than once with new gas.) I got back in July of 2020 and the jeep was running just as well as it was when I left it. After getting out of quarentine I decided to do a little fluid level check on it. It was nearly completely empty of oil. I drove it to the AutoZone down the street to get some oil and on the way there my the CIL came on with a code for the oil pump. I unplugged the battery, filled up the engine with oil (temp fix) and the code went away. handout a week later I got a code for my sensor 1 bank 2 o2 sensor. I replaced it and the code went away. About a day later the CIL came back on with a P300 and P301. I replaced all of my plugs and coils. No code for about 1 day, then the misfires started to spread to the other cylinders (with this being said, I didn't have a real scanner tool until this happened. I was only using the AutoZone loaner which was only showing the cylinder 1 misfires. so the other misfires may have been present, but not sending a code) anyway...took it to the dealership, they did the whole Left head extended warranty fix. They said it was good to go...it was not good to go. long story short, they had awful customer service and were taking forever to give me any kind of process to I took it back to fix it myself.

I'm not only getting 1,3,5 misfires. they're intermittent and don't always happen in tandem. They also only happen while at idle in any drive position ie. P,R,D. As soon as I accelerate they go away and the engine is smooth as all hell.


I started to put some small parts in to see if they would remedy it:

all work was done on bank 1

cam position sensor

crank position sensor

VVT solenoid actuators? I think is what they're called.

swapped coils, plugs, and fuel injectors from the other bank (also cleaned injectors)

new PCV valve.

new senor 1 bank 1 o2 sensor


I'm running out of options...


Thanks for reading,

 

So, my 07 is having a random misfire code. Just the p0300, no specific cylinder. I have replaced a bunch of stuff in addition to the crank position sensor, and PCV valve. My spark plugs are all dirty on the drivers side (2, 4 and 6) and clean on the passenger! 1, 3 and 5. I need some help here, thinking about getting it in the shop, but I fear shops nowadays. Did the PCM actually work in the first poster's situation? Anyway good luck to the folks!