1998 F150 V8 4.6L (165,000 miles)

My truck has a rattle in the Catalytic Converter (Not the pre-cat) when you hit it with your hand, or drive down the road. No codes are being produced. About a year ago I solved the misfire and P0420 Code problems and CEL flashing. So is the Catalytic Converter bad? After some research it seems that there is a consensus that the Catalytic Converter doesn't go bad. Is this true? The truck runs fine, but it sure seems to me the Catalytic Converter needs to be replaced. If I replace the Catalytic Converter should I also replace the Pre-Cat?

 

If your cat is rattling internally, the substrate has broken and it should be replaced before a chunk blocks your exhaust flow.

Doesn't sound like any need to touch the pre-cats.

 

I am new to this site but i am an ASE cert. master tech and an L-1 (advanced engine performance specialist) But the answer to your question is yes the converter is bad,It's substrate has been melted an this is almost always related to engine performance issues (misfire) the reason that you are not getting an efficiency code (check engine light) is this converter is not monitored (the pre-cats are) I would be sure your engine is in a good state of tune (plugs coil packs etc. before replacing the converter) and the answer to your second question is no if you are not getting any efficiency codes there is no reason to replace it!

 

Catalytic Converter

This is from the hyperlink above. A lot of useful general information can be found on this link.

"Some degree of restriction inside the converter honeycomb can also be caused by accumulated deposits: phosphorus from oil burning and/or carbon from oil burning, a rich fuel mixture or frequent short trip driving where the converter rarely reaches light-off temperature). Physical damage to the honeycomb as a result of road hazards or severe jolts may cause the relatively brittle ceramic honeycomb to break or crumble inside the converter shell. A rattling noise when you shake or thump the converter would tell you there's loose debris inside. A undamaged monolith converter should make no noise."

 

I had one I thought was bad, but the heat shield that was spot welded on it just came loose, so might want to check that also.

If the truck ran rich or with a dead cylinder at one point, it's very likely the cat is toast. The unburnt fuel will cause it to overheat and destroy itself. If a truck has zero problems throughout its life, it's possible the catalytic converter can last the life of the vehicle, but it doesn't always work out that way.

 

Well I had the rear cat removed and the pre-cat was bad also. Torched 'em both from a previous misfire the engine had. After the install on Wednesday the SES or CEL illuminated. I ran the OBD-II scan tool and found P0135 and P1131. The mechanic forgot to plug in the O2 sensor. Sure glad I checked that before trying anything else. Not sure if the posted pictures here will work.