I bought my 12.2005 STR a couple of years ago. The car was already throwing out p0420 and p0430, most likely because of the 2 previous owners ignoring vacuum leaks.
I fixed the brake booster leak (thanks to the info I found here) and the after cat o2 sensors, but the damage had already been done. At full throttle they smell typically like rotten eggs, also the car seems a bit sluggish at times.

I've read the threads here and some swore that the 59975 high flow cats from Magnaflow are a great deal. Others said they melted after bout 15.000 miles, which is awful if true.

Do you guys have any experience with them or with replacement cats in general?

Thanks !

 

Take out one or both of the O2 sensors out of both cats and look at the catalytic material inside to see if it’s clogged up. As far as I understand it’s supposed to smell like rotten eggs it’s bad when either it smells like a regular 1970s truck exhaust or it’s clogged up. Maybe I’m wrong, but I thought they were supposed to smell like rotten eggs. I thought that was a sign that converters were catalyzing.

 

Sounds like the fuel has more sulphur (sulfur) than I'd expect - typical of the USA? (Very much not the case here in the UK)

 

Ignore what I just said I just found this on the Internet;

 

Yeah, I'm pretty sure they're baked. My mechanic, who inspected them, said the same.
@JagV8 I live in Germany, we should be running on similar fuel as in the Kingdom.

200 cell cats are accepted here for TÜV (MoT), trying to look for a suitable replacement that won't break the car, themselves or my pocket

 

they melt bad