Why does my 93 caprice smell like rotten eggs?

The smell of rotten eggs is due to a compound called hydrogen sulfide. This comes from the small amount of sulfur that is present in the fuel. Normally the sulfur is converted to sulfur dioxide, which has no odor. When the converter breaks or the filtering layers have worn down inside the converter, the sulfur is not transformed into the odorless form. Therefore a strong rotten egg smell is produced. Another possible cause for this smell may be that the converter is plugged. Unfortunately you cannot repair a converter but need to have it completely replaced. Two other causes of rotten eggs besides a broken catalytic converter include an engine that is running too hot or a broken fuel pressure regulator. You can easily deal with the fuel pressure regulator by replacing the fuel filter. Ensure fuel pressure is ok and excess fuel not being dumped into convertor, but if that were the case, you should have mil on for running too rich, also try changing gas stations-some brands mix and or have more additives. If you must change convertor go to a muffler shop-they do it routinely and pretty cheap. You may also have a code pop up soon for 02 sensor behind convertor which monitors it's efficiency. If excess fuel is causing your problem, eventually it will start killing your O2's.