Bad exhaust smell
 

I rode the motorcycle to work this morning and when I came into town I got behind an F-150 like mine and his exhaust smelled like a combination of battery acid and rotten eggs. It was so bad it burned my nose and eyes. Couldn't see smoke but it was a lot stronger when he accelerated from a stop light. I was just wondering if he was burning something other than gas or if he has a serious engine problem and what that might be.

Usually the rotten egg smell is an indicator that the catalytic converter is shot. I don't know what causes the smell, or what determines that it's shot. The internals of a cat are a ceramic type of material - maybe asbestos??. I hollowed out a cat in a Mustang I had.

his cats were either bad, or going to be bad very quickly.

he's probably been running really rich and fouled them up. or he may just have really high mileage.

Yep, sounds like a bad cat. The rotten eggs smell is the telltale sign.