@edgarblythe,
Sounds like a classic case of the The Man sticking the Little Guy right in the neck (at least the way edgar tells it).
If the seller knowingly misrepresented the condition of the car you have recourse, but you will need to consult an attorney, not a bureaucrat.
You bought a used car. Did you really think you were buying a cream-puff?
You've neglected to tell us if you bought the car from the owner or a dealer. Sounds like it was a private sale.
A bad catalytic converter (or two) is by no means the same thing as a bad engine. They usually last for at least 100,000 miles or so and therefore I am assuming the car you bought wasn't owned by a little old lady who only drove it to church on Sundays.
If you buy a used car that has high mileage, it only stands to reason that you should expect it to have some wear and tear issues.
You've left out a lot of information so we don't know what year the car was or how much you paid for it, but unless the CC was defective, the car was old.
I don't have a problem with a law system that assumes people have common sense. Deliberate deception is something that can overcome common sense and Texas law addresses such a situations. Contrary to the common belief among Yankee Libs, Texas doesn't embrace bandits.
If you need the government to hold your hand through every transaction you conduct as an adult, and to step in and protect you from stupid mistakes, you shouldn't live in Texas.
It sure would be nice if everyone in the world was an honest and honorable individual, but of course they are not. You don't have to be a cynic to be skeptical.
Caveat Emptor