1997 850 glt
I think the cat maybe clogged

 

If you start to type this into google it comes up with "clogged catalytic converter symptoms" before you finish "cat". Lots of stuff, YT and more.
I remember a smell but can't remember what it was like.

 

Cat's give off a smell via the exhaust not unlike sulphuric gas or rotten eggs. The smell is also similar to that you get from geothermal mudpools but obviously only to a very mild degree.
Usually detectable when you have just parked up in your garage or a confined area.

 

Should get a CEL.

 

I get codes 0172 and 0455

 

if you have a heat thermal temp sensor you can check your readings at the front and rear.

that is what I did and had 200 deg at the front and 110 at the rear, plus I would get a CEL too.

 

If it's starting to clog one of the first symptoms will be that at higher engine speeds, freeway speed you will hit a wall at which point pressing the accelerator will not affect the engine. As the cat clogs it progressively limits the amount of air the engine can pass. It would be fairly normal and feel responsive until close to that maximum flow and then it's like a rev limiter where you just lose power. You can hold that speed but you can't increase it.

Temperature is also an indicator but it's a little dangerous trying to take readings unless you have an infrared temp detector. The temp at the end of the cat should be hotter than the temp right at the inlet.

The back yard way of doing a test would be to open the exhaust up at or before the cat and test drive to see if it responds better.

 

I get 350 before and 320 after the cat.CCEL on codes 0172 and 0455.

 

Why do you think the cat is clogged ??