the lead additive coats and pugs the catalyst, rendering it as useless. since lead has not been used since 1992, this should not be an issue. the purpose of lead in the fuel was to preserve the valves and seats. with hardened seats and valves, it is not needed.
The lead in the fuel will contaminate the converter and it will cease working.
the lead plugs up the cat.. causing it to fail and throwing a CEL and having to replace the cat..
