Exhaust fumes rarely smell particularly fresh, but on occasions, catalytic converters can emit extremely pungent odors, which can sometimes be smelled both inside and outside the car.
A rotten egg smell is often related to sulfur. In this particular case, it is possible the catalytic converter contains a buildup of sulfur. The root cause of the odor is usually worn or overworked parts.
Aside from the presence of an unpleasant smell, the odor can be a symptom of parts working inefficiently. In a catalytic converter, this can mean two things: the emissions from the car no longer meet required standards, and the car's performance may also be suffering.
Unfortunately, solving the problem usually requires the replacement of at least one part. Often the worn part is something simple like a filter, which is relatively straightforward to replace. Identifying and replacing the worn or damaged part is best performed by a trained mechanic with access to proper emissions-testing equipment. However, if the odor is only emitted after an occasional period of heavy usage, the problem is unlikely to be serious enough to warrant a repair unless it becomes a regular occurrence.
