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I installed a MagnaFlow HiFlow cat on my 1999 SSE about 4,000 miles ago. Since that time, if I am at highway speed and punch the accelerator to pass or for whatever reason, I smell something like rotten eggs or sulfur. Has anyone else had this problem or does anyone have any idea why this is happening? I thought at first it was due to it being new and need to "burn off" whatever, but I would think it would have done that by now. Thanks in advance for any thoughts.

Isn't the sulfur smell a sign of a plugged cat?

When I put a Magnaflow on mine, it smelled like that for a little while. It went away.

If the cat was plugged, I'm certain there would be performance issues. It runs like a watch. I put it on in 2008 and have only put 4000 miles on since then as I only drive it a bit in the summer. Maybe it just hasn't been run enough. The smell only lasts for a minute or so just after I jump on it.

I have smelled similar, I suspect its carbon or partially burnt fuel. Something like that. Maybe even deposits knocking loose or something.

I smell it from a lot of cars that get romped on on the highway.

Can't really help pin down the issue, but I can say I replaced my cat about ~5,000 ago and occasionally get the same smell on the highway when my foot decides to get a bit heavy. Never had the smell from the original, all I can really assume is that it's not a big deal, especially since I only notice the smell at about 85-90mph

Thanks for the reply guys. I didn't think it was anything serious, as there is no performance issue. It is just annoying and I was wondering if it was a common occurrence.