Motor runs independently of the catalytic converters - unless the cats
are blocked from the honeycomb being loose and plugging their exits.
Usually, one hears a lot of rattling beforehand. CATS are expensive so
don't jump at this unless you KNOW they need to be replaced. After
market CATS are available for less $$.
Sulfur odor is from the fuel. Forget it, that's NOT the problem.
Are you telling us that after the fuel pressure regulator was installed
the engine ran much longer but was noisy?
If so, then "the problem" is fixed and you need to replace some exhaust
parts that are leaking and therefore noisy. First check the joints
between pipe sections, then the pipes themselves and the muffler.
There's an exhaust leak somewhere and that's creating the noise.
Why do you think its exhaust suddenly "smokes like crazy"? This is a new