I had the phosphorus smell for a while now and its always when the engine would run at high rpm. However, there is no performance loss. Is there a way to check blocked cats without taking them by checking the airlfow any way? I would like to put in a y pipe to get rid of the possible faulty cat but fear Iwont pass inspection since last time during inspection, the mechanic was very picky and checked the whole exhaust.
Car has 95k miles, no engine mods.

 

If your not having any power loss your cat is not plugged. A plugged cat can make a car very sluggish or not run at all.

To diagnose a plugged cat on a car that is running poorly you either drill hole in front of it(you would need to weld the hole back up of course) or disconect the pipe in frot of it to see if freeing up the exhaust will make the car run better. If it's one of the precats you would have to disconect them from the manifold. If you are having a cat problem most likely you would have a ses light because are O2's read cat efficiancy. The smell could be the cat going bad but going bad doesn't always mean plugged

 

I did have the ses light on with the code P0420 ( bad cat) at about 5k mark when the car was brand new. Dealer tried to take care of it 3 times or so, light kept coming back so I just ignored the light since car felt fine. O2 sim keeps the light off as of now. oxygen sensors were all replaced.
I took a look at the bolt heads that hold the cats and they are all rusted and almost impossible to grab with anything. Any way to remove them by myself or i will need to go to a mechanic to have them welded off ?