I have a rattle coming from the exhaust on idle and take off. I don't hear the rattle while driving. Any thoughts on further diagnostics to tell what it is?

 

Crawl under the Jeep and knock on the cat. If that is whats rattling, its time for a new one.

 

How do you tell if it's the cat or the heat shield?

 

shake the shield...then beat the cat.

 

Yeah don't beat the cat. You have a 100% chance of it being broken then...just shake the cat up and down.

 

Roger that...

 

Beat the cat, I hate cats.

 

You just wanna see if it rattles.


Hahahaha

 

Inside the cat, is a ceramic honeycomb core.

Sometimes they get a "hot spot" inside & start to crack. Then little chunks bounce around & sometimes work their way out & fall on the ground behind your vehicle.

This would signal a possible fuel mixture problem & the unfortunate end of the converter.

 

I've got 160k, so could it be it's just wore out. I wouldn't assume a fuel mixture problem at this point...

 

If you do have a bad cat, replace it with this one.
http://www.davesport.com/cgi-bin/davesport/DCAT100.html
It's a metal cat that will handle the exhaust temps of a Jeep and it will flow better than most other cats.
Some fabrication will be required, but a muffler shop should be able to handle it.

 

i gad a rather long post about how to beat cats before i deleted it there....

 

Check EVERYTHING !!!!!!!!!

And I mean EVERYTHING !!!!!!!

I thought my CAT was rattling, even began looking into which one to order.

Then one day, while in the driveway idling, I heard something fall to the ground and the rattling stopped!

It was a CLAMP that was rusted off.

Push/Pull/Tugg on all the clamps and hangars.

 

The most common cause is the heat shield. In most situations the heat shield is wrapped around the cat like a clamshell and is held together with spot welds. They rust and separate, causing a rattle. I've fixed many by locating the offending weld then drilling through the weld with a self-tapping screw.

 

All the diagnostic stuff is great. Keep it coming. There's nothing like experience.