2008 JK 3.8 misfires, P0304 and P0300

[cpwolf]

Okay, sent my son off to Ft Campbell 101st with his 2008 Jeep Jk. Had it running well.
He, as a young kid not focused, did little or no maintenance. Says “Dad I bought a used Ford Ranger, the Jeep just doesn’t run well”.

I get it transported home.

Muffler is rusted half off. It’s now banging around, slid off the Cat Y pipe but not before pulling and yanking the cats loose from the exhaust manifold.

1. I replaced missing cat to manifold in driver side, and tightened cat y pipe.
2. Tune up, new plugs, wires and Mopar Coil. Wow, 4 plug wasted, all of them were wow, 4 worse.
3. oil change (quart + low argh)

He drove it a lot, said yes it was blinding CEL you name it, so who knows. I know it needed the plugs/wires/coil.

now I don’t want to throw parts.

I drove it, Cats aren’t connected to exhaust and new muffler yet, but it is Misfiring big time, blam bam bam

So, trying to get a good idea of what all this can be and best order of ops

1. With all the misfires, and Cats disconnected some, they may be blown. How do I check?
2. O2 sensors?!! I’m not getting a code for them?
3. I don’t have compression tester, but is this a test I need to run here?

any thoughts, I’m exhausted with fixing this Jeep every time he’s away and I see it. Last time had to get a new Intake Manifold, the sensor the PO must have cracked installed temp sensor and JB welded and it gave. Super pissed.

He hasn’t rotated expensive BFG 35” MT and I can see the fronts have worn bad, argh.

Any organized suggestions appreciated.

 

[pc1p]

How many miles does the Jeep have and how long was it sitting? If it's been down for a while, gas can get wonky fairly quickly, especially in warmer climates.

It's possible, though rare, to have clogged cats on modern vehicles. If you had them off and could blow air through them, they're fine (for flow).

If you had a cylinder not firing for a while, it's very likely packed with carbon build up. Assuming the valve is able to open and you're getting flow, it could very well clear up with some fresh gas and time (and a few heat cycles). I would connect the exhaust and give it a few drive cycles. At that point, if there is no improvement, I would certainly do a compression check.

 

[cpwolf]

It hadn’t sit no, it was my sons main driver.

Fresh gas and maybe SeaFoam can’t hurt, agree.

 

[pc1p]

Some SeaFoam through the vacuum port would help too... worst case, it just clears any mosquitos out from your neighborhood

Have you driven it much since your last update? Any changes?

 

[cpwolf]

Ok.....just to follow up here......a complete Dumbass worked on my JK. That dumbass fixed the all of the exhaust that his dumbass son let fall apart and create a lot of this problem on the #4 misfiring and exhaust leaks, you name it.

So, the dipshit then did a tune up, new coil, plugs and plug wires. NOW still trying to figure out why I"m seeing misfires on #3 and 5 and all kinds of F'd up readings on the Jscan.

Well, I know where my son gets it....I had 3 and 5 wires backward. Stopped and said retrace all your steps here. What did you do...walk yourself through.

Switched...bam, no more misfires...all fixed for that.....Dammmit.

So a nice tune up is very helpful...if you connect the wires correctly...which by the way came with labels on both ends....ha. That dumbass is me if you haven't guessed.

I looked to sell it, and a guy took it to a shop. He got a nice rundown of every maintenance needed...which I frankly new a lot of. Just that he paid and backed out...so I got a nice list of their thoughts too.

Just going to get it all fixed and see if I might keep the JK for a 3rd Jeep....and my wife will flip out..but hey, I like Jeeps.

 

[BLACKJKU]

Ok.....just to follow up here......a complete Dumbass worked on my JK. That dumbass fixed the all of the exhaust that his dumbass son let fall apart and create a lot of this problem on the #4 misfiring and exhaust leaks, you name it.

So, the dipshit then did a tune up, new coil, plugs and plug wires. NOW still trying to figure out why I"m seeing misfires on #3 and 5 and all kinds of F'd up readings on the Jscan.

Well, I know where my son gets it....I had 3 and 5 wires backward. Stopped and said retrace all your steps here. What did you do...walk yourself through.

Switched...bam, no more misfires...all fixed for that.....Dammmit.

So a nice tune up is very helpful...if you connect the wires correctly...which by the way came with labels on both ends....ha. That dumbass is me if you haven't guessed.

I looked to sell it, and a guy took it to a shop. He got a nice rundown of every maintenance needed...which I frankly new a lot of. Just that he paid and backed out...so I got a nice list of their thoughts too.

Just going to get it all fixed and see if I might keep the JK for a 3rd Jeep....and my wife will flip out..but hey, I like Jeeps.

Glad to see that at least you admitted it was fixer error.

 

[Cimmerian]

so I got a nice list of their thoughts too.

Please include this list. Not that I want to laugh at your misfortune or anything.

 

[cpwolf]

Please include this list. Not that I want to laugh at your misfortune or anything.

I was mostly laughing at myself....I just rebuilt the drivetrain on my CJ5, replaced the timing cover and rms and all of the front of the v8 AMC 304...and then I get to work on our JK...and flip wires that drive me down a rabbit hole...ugh.

My son drove it for thousands of miles with the muffler hanging, that in turned pulled the exhaust apart and loosened the exhaust manifolds....so I was concerned O2 sensors might be burned or wires pulled, which I thought was a part of the misfires.

So when I did the wires wrong, threw me.

So I fixed exhaust, the wire swap quick fix the misfires all gone. They were reading a ABS failure, said needed a full control module? I was like "WHat" Where did that come from When I got it back, using my tow bar...the battery was dead? Not sure why...but I pulled the cables, charged for a couple days to full....and reconnected and all the ABS and brake faults go away. I read a lot that ground and voltage drops will cause that, number one reason...strange they were searching and charging $2k to fix....when they battery was almost dead causing it.

They did point out leaks....Front axle seals, rear diff cover...which wasn't there before that I saw....and I was losing my mind that here and there...you'd see coolant on the engine.....and they found a crack in the thermostat housing.

So I have inner seals, on and suggested new front DS u joints, probably good to replace, and I'm going to clean the heck out of it and do a top down leak black light check.

Just since you asked...and my wife will be annoyed that I want to keep it now....since I have a TJ and a CJ5 in the garage...and the JK in the driveway, ha. But frankly, I can leave the top on that and off my TJ and CJ and always have a vehicle ready to go, ha.

 

[Cimmerian]

Yea the JK would be the best Jeep if weren't for all the grounding and electrical issues. Last year I said fuck it and replaced every grounding wire on the thing and it helped a lot. Those OEM ribbon wires are extremely thin.