My catalytic converter gives off a rotten egg smell every now and then and it's been doing this for years. I just got my WSP Y-pipe and while I'm working on the exhaust I think I'll replace the cat but I've heard you should find the underlying cause behind a problem w/ the cat. It's puzzling because the car runs great. Anyone know why the cat would make this smell?

 

when a catalytic converter goes bad, that's how it normally smells
I'd recommend replacing it. You can get a high flow cat from WSP also and it'll be cheaper than a new stock replacement

 

Sometimes if you are travelling very quickly for a long time and then slow down suddenly, the sulfur builds up in the catalytic converter and makes the smell. It doesnt necessarily mean the cat is dead. If it smells like that very frequently though, it probably is done for.

 

I have read that the way a cat smells is dependant on what it is made out of. IE a cat made out of X will smell more of Sulfur than a cat made out of Z. I know that many new cars stink of sulfur from the exhaust and this is obviously not from a bad cat. This was in Car & Driver I believe.

 

doesn't whether or not it is a 5 sp or automatic have somethign to do with it, or am i crazy?? I used to remember a few of my friends 5sp (that were fairly new) smelling bad when idle.