Boombrewer

So I've been periodically getting and clearing a p0430 and p0420 code (sometimes only one, sometimes both). I've figured out the bolts on the joint where the cat connects to the exhaust header are vibrating loose. I'd tighten them up and it would be good for weeks or months and progressively shorter amount of time to now they won't stay tight more than 10 miles. I think the motor mounts might be worn out (hear a lot of movement when I aggressively disengage the clutch). Count the bad motor mounts cause excessive vibration loosening the bolts? Crazy sounding I know but I got nothing else.

Its a 2009 JKU with about 135K miles and stock (with a manual tranny).

Mr.T

Could be. Maybe mount a gopro or cell-phone camera and see how much movement is going on. How loose are the bolts getting? They might be stretched enough that they're about to break. Might want to remove/replace the bolts, and inspect the tapered portion of the pipe and exhaust manifold where they seat and make a seal.

Boombrewer

The bolts are only getting like a turn or so. I hadn't thought about them stretching. I'll have to pull them and take a look. I first discovered it as the cause for the code when I was about to replace the cats and realized both sides were loose. Thanks for the advice.

Mr.T

One more thought; the nuts are captive in a clip and tend to spin, soak with penetrating oil beforehand. Both the captive nuts and bolts are readily available from mopar dealers (internet or local).

Boombrewer

There are no nuts on mine. The collar is threaded. One of my "solutions" to the problem was to just put nuts on the other side and create a friction lock between the nut and the collar. But they clearly are designed to stay tight, so something else must be going on and I'd rather find the real cause rather than "rig a solution."

karls10jk

You've got aftermarket manifolds. I never had an issue with the stock manifolds staying tight but my Dorman's loosen up occasionally as well. I considered the friction/ jam nut idea you're talking about but I think the issue I ran into was clearance for the nut. I'd like to find an affordable solution like Stage 8 Locking Fasteners, they appear to be the solution to exhaust bolts backing out. You create a mechanical lock so they can't back out. I just tighten mine from time to time, really should find a solution though because the Jeep does run better when the system is sealed. I don't think it's motor mounts though. They're pretty much a "lifetime" part unless something catastrophic happens. If you replace the motor mounts, stay with the factory mounts. Don't be tempted to go with poly. They'll rattle your teeth out.

Boombrewer

Thanks for the heads up and info. Surprisingly, the bolts were still tight. Not sure where the rattle is coming from though. And I disconnected the negative battery capable to clear the CEL so we'll see if it stays off and the bolts stay tight now. The next thing I'll check is the taper though. Bolt stretch is the best idea I've heard so far.