Troubleshooting small sounding misfire with P0301, P0431, & P0123 codes

[Matt14]

This started after an off-road trip on the way back had a really bad misfire in cylinder one. So bad I had to end up towing it home.

Ended up replacing the spark plugs, and that fixed it for a while. They were really poorly gaped (i didn’t know gapping was a thing lol).

To sure things up I went and changed out the fuel injectors about a week later. I fell into the trap of the 4 hole injectors and after that I had a slight miss but not enough to fire a code. I swapped back in the old ones and it didn’t get better.

I changed out the TPS with a Mopar replacement after that and it didn’t fix it either.

It’s been like that for about a month but today the following check engine codes just popped up:

P0301 - cylinder one misfire
P0431 - warm up catalytic converter, bank 2 - efficiency below threshold
P0123 - throttle position switch, accelerator petal position switch a - high input

Any thoughts on what to try next?

Seems like I might need to replace the O2 Sensors and / or the catalytic converters but would that cause a misfire?

My next thoughts are:

• New coil pack
• New O2 sensors
• New catalytic converters
• New Mopar fuel injectors

I have a 2006 Rubicon with about 140,000 miles on it.

Thanks for all the help.

 

[Matt14]

Update:

I took it to the shop and had them do a diagnostic. They thought it was the coil pack which they replaced. The code one away, but it still sounds like it’s missing at idle.

The catalytic converter code came back so looks like I’ll need to replace the cats. And they said the O2 sensors are OK so I don’t think that’s the culprit.

Can bad catalytic converters cause a misfire or rough idle?

 

[Matt14]

They are saying it could be due to a compression issue. They found cylinder 5 is about 150 PSI and the others were 170ish if I remember what they said correctly.

Which they say it isn't causing a misfire, just a rough idle. They also say this may be what is causing the P0431 code and that the cats aren't bad yet.

Anyone have any thoughts to add with any of this?

 

[JKP]

Check the mini cat to manifold bolts. If they are loose it will throw the cat efficiency codes.

 

[Lil' Cheesy]

Sorry that this is kind of a repeat, but there's too much content to read through it all. My 2004 jeep wrangler has the CEL on, and very quickly after driving it, it starts flashing. Its throwing code P0301. I've installed new spark plugs, checked the fuel injectors. I've tested the plugs by having the coil rail off and a plug in it. It sparks when turned over. I've also swapped the plugs between cylinder 1 & 2. The code stays on cylinder 1. I've also swapped fuel injectors between cylinder 1 & 2. The code remains with cylinder 1. I played around with the O2 censors. They threw their own codes then code went away after reconnecting. I've disconnected the battery to clear the codes completely, but p0301 returns and remains. My next step is a compression test. That is unless someone on here knows something else I'm missing.
Thanks for the input. Seems to be a lot of good info in this forum.