smelly catalytic converter?

Found this with a google search.

There's sulfur in fuel additives; your engine isn't burning it completely and your catalytic converter is storing it and then releasing it as hydrogen sulfide when you add load to the engine and force more air through.

Try switching gas stations, or fuel grades; then try a thorough tune-up: replace the spark plugs, plug wires, fuel and air filters, and oxygen sensor, and clean the fuel injectors.

If that doesn't do it, replace your converter.