I have an 05 Hyundai Sonata with 112k miles. Its in the shop right having a new engine installed due to low compression in one of my valves. I'm also having the belt, tensioners, and water pump replaced. My mechanic called me today and said the engine is in but there is another problem, the catalytic converter needs to be replaced and claims that it was what created the engine problem in the first place.

Can anyone tell me if I should call BS?

 

Call BS..

Cats are killed.. cats dont kill.

Start it up without exhaust.. then install exhaust.. if it runs, all should be well.

If the cat was killed, depending on cat, engine will run fine, and ox sensor logic in PCM will determine if cat is doing it' job (efficiency).... or the cat will be restricted and car will not get out of it' own way (have a bad case of the BLAAAAAAAHS when trying to accell rapdily).