One problem related to catalytic convertor has been reported for the 1998 Nissan Altima. The most recently reported issues are listed below.
Rotten egg/sulfur smell emitted from exhaust. First service performed on vehicle was to replace the on-board computer. This did not fix the problem. Took the car to another dealership and they said there wasn't a "fix" available. A workaround to avoid the smell is to burn premium gasoline. Premium gasoline does eliminate the odor, but the manual says I need to burn gas rated at 87 octane. I shouldn't have to burn premium fuel, which is much more costly, to avoid this problem. I believe this problem to be a engineering defect, and want the problem resolved.