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Discussion Starter #1
I am replacing the cats on my 2010 with the hemi. Replacing because the drivers side cat rattles like crazy when cold or accelerating but it has not thrown any codes. I ordered the front assembly from Jeep and need some advice from those who have done this (please).

I have the shop manual but wanted to hear "real world" experience from those who have done this.

Thanks in advance.
 

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That's an expensive guess, and probably not your issue if you're not getting catalyst efficiency codes.... not to mention the cats are probably still covered under warranty IF they are bad.
 

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Rattle is a tough noise to determine the issue. Although, a noise when cold and accelerating falls into a more known issue. Leaking exhaust manifolds will produce a higher pitched sputter which sounds almost mechanical. The original manifold bolts suck and the midpipe section hangs on the with a decent amount of weight. Many folks, myself included, find the back two mounting bolts on each side broken.
Have you done engine work before that involved decent surgery? Change intake? This job is similiar in work level, but not impossible for someone with basic skill.
Even easier if your jeep is lifted with bigger rubber.
It takes alot to brake the interior of a cat converter, which is why i think you have the normal commander leak.
 

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Discussion Starter #4
Thanks for the replies. I checked the manifold for leaks both visual, smoke test and even pressurized the system so I know that gaskets were good. Determined cat rattle using a stethoscope and isolated it to the drivers side. Sounds are normal on drivers side from exhaust manifold up to the cat. Then you can hear it downstream to where the 2 pipes connect. Passenger side cat exhaust sound is the same from manifold back to the welded connection of the 2 pipes.

Also, if you use your fist and hit the cat you can hear something moving around inside. Passenger cat returns a "thud" sound.

Reason I am replacing myself is I don't trust dealers or others to work on my cars. Big difference between guy who does it for money and the owner who does it because he wants to. They won't put the level of care that I would.

Mechanical experience? Been working on my own cars since late 1970's. Even rebuilt a 1948 Packard 327 CID Straight 8. Intake/Exhaust manifold on that one is pretty hefty. And yes, you can balance a quarter on edge on top of that engine while it is running. After all, it is a Packard. LOL.
 

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Considering everything you've done so far for diagnosing, only couple of things left I could contribute to what may be.

1. The midpipes, at least on my OEM kit, are twin tube (one inside the other) and you may have rust/debris inside the walls between the tubes.

2. You might have something actually in the cat (forward of the cat is scary). Any weep holes in the muffler which may let in small debris?

Might as well drop the midpipes now, definitely need to check them out. Then just cut out the cats and replace with high flow cats. Maybe cost just under $700 if you go with the magnaflows that are made to work with the sensors. I went this route after the first set of high flow cats I bought did not pkay well with the computer.

Dave
 

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Discussion Starter #6
Mk153smaw: Thank you, food for thought.

The noise is most prominent when cold, but calms down once the cat heats up. Even warmed up though, you can hear a "tinny rattle" on slight acceleration.

I do know that the manifold gaskets were replaced by the PO at a Jeep Dealer and I wonder if something dropped into the pipe when they were disconnected. The noise is from the cat and back, really resonating through the pipe up to where it connects to the passenger side pipe. On the passenger side you can just hear the exhaust flow nice and smooth. Whatever it is, it is definitely starting at the cat.

But like you said, only one way to find out and that is to drop them.
 

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Yeah, at this point you have to see them. It is an odd problem though... The rattle is occurring cold and after heat up (expansion) there is less. Could possibly be a spot weld that let loose from vibration? Or rust late from the flange itself? my flange (mids to muff) was ordinary metal and completely flaked (2006 though).

Additional work, but after you drop the mid pipe I would drop the passenger manifold just for giggles. Passenger side is cake and would only take a few minutes once the mid pipe is down. At least you would be able to inspect the bolts. Wether they are an issue or not, no better time to check really...

When I purchased the new manifold parts, I noticed that the grade and material of the bolt is vastly better than the original stuff.

Driver side is a massive pain in the rear (not really), but I am so picky about bolts and their age that I tend to check all that crap unnecessarily sometimes.
Being a former Cherokee owner has made me paranoid!

Dave
 

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Discussion Starter #8
Just an update on my work.

I replaced the cats which was not as bad a job as I thought. After replacement, I disconnected the battery ground for 30 minutes to reset the computer with the following results after 200 miles:

1. Exhaust is quiet on start up. NO rattle at all. I did look as best I could inside the old ones, but could not find anything definitive as a cause.

2. My MPG went from an average of 14.2 to 16.1 mpg!

3. Performance has also increased for the better as well. More responsive.

4. Much smoother going in and out of MDS.

I will never know what was really wrong with the old setup, but obviously there was something wrong going on inside there.
 
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