Running rich

[Jmcreynolds86]

Could bad plugs or coil packs be causing my expedition to be running rich enough to burn up brand new cats in a little over two weeks? I had two broken manifold studs so I replaced all of the studs and put new cats on along with new o2 sensors and a little over two weeks later the driver side cat is rattling.

 

[docraymund]

Bad plugs or coil packs would cause unburned fuel to reach the cats but not necessarily make the engine rich. If your new cats rattles then you may have purchased a defective piece.

 

[rjdelp7]

Running it with a misfire, will kill a cat. You will have a CEL and code. You would smell it in the exhaust. A loose heat shield could be the rattle.