When should the catalytic converter be replaced? I don't have any symptoms of failure. Do they make an off-road pipe to replace the CC? I have an 09 5.4L

 

They do make an off road pipe, but Federal Law says if your Catalytic converter goes bad you are supposed to replace it with the same Part in the OEM location. Off road pipes are just that, an off road pipe not for use on an Emission controlled vehicle.
I had a friend that put long tubes and High flow cats on his truck and was written for other than OEM cats and it had a $15000 fine attached with it. He got the ticket at a DUI check point.

 

Damn the DUI would have been cheaper!

 

look into the mess of trouble you'll get in for removing DEF System on a diesel

 

If your cats EVER go bad, there's something wrong with your fuel system. They should never go bad if things are running as they should. If they do go bad, you know something is wrong with your fuel intake system.

 

^+1

Cant's only fail when something causes them to get "plugged". Fix the issue before replacing the cat if necessary.

 

I have no apparent issue, just a 150K on the odometer.

 

Then you have no issue.

 

Well, they can also rust to death. BiL just got new cats on his "new" 1998 car since so many pieces of the exhaust were falling apart.