Novak Conversions Jeep Wrangler JK engine mounts

2008 JK 3.8 Misfires p0304 p0300 and mistreated

cpwolf

JK Enthusiast
Supporting Member
Joined
Aug 17, 2020
Messages
135
Location
Cedar Park, TX
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.

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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.
 
Novak Conversions Jeep Wrangler JK engine mounts