What is the correct catalytic converter for a 2004 f150 4.6L

The correct catalytic converter is the original equipment one. Check with a local exhaust / muffler shop near you for further advice for custom information; with this highly regulated emissions control component, deferring to the Ford converter is best typically, and in some parts of the country, the law.

I always recommend installing the factory catalytic converter. If you can not afford that you can contact a muffler shop and have an aftermarket installed. Catalytic converters have precious metals in the for the reaction to clean the exhaust. When price is cut so is the amount of these metals. The aftermarket converters tend to last about 18 months from my experience.