Catalytic converter failure is common. Internal components become loose, causing a rattle or creating back pressure in the exhaust.Google+
Car Problem Reports
Ford Crown Victoria Loose internal components may cause catalytic converter failure
Ford Crown Victoria Problem
Visitor, 2005 Ford Crown Victoria, 88,000 mi
rattle right exhaust, replaced $900.00
After I changed my coil on my vic my converter began to tap and have a hard time gaining speed.