94 BMW 525 failed emission second year in a row after replacing catalytic converter 12 months ago

If the cat has indeed failed, it's probably because the engine is either running rich or else burning oil. Do you have excessive oil consumption? How much oil does it use? If not a lot, have the fuel injectors checked and cleaned, and have the O2 sensor replaced (if the cat is done, likely so is the O2 sensor.) If it is using a lot of oil, that needs to be fixed before replacing the cat - with that mileage it might be easier to drop in a low mileage junkyard engine.

good luck

nate

If you replaced the original catalytic converter with a low quality replacement unit, then this could also be part of the problem. All catalytics are not created equal.

How should anyone know? We don't know what your emissions numbers are and what any of the measurements were. Not only that, we don't know what the numbers out of the engine control system are.

If someone replaced your converter without checking to see the converter operation, they wasted your money, yes. The numbers let you see what is going on.

If you posted actual numbers here, someone might be able to make a stab at what is going on. 321K isn't a crazy amount of mileage for one of these engines, but you might have all kinds of things wrong with the engine that could be dumping junk down the tailpipe. If you're misfiring or running too rich, you can dump a lot of stuff into the converter that it can't deal with, especially if it's a cheap aftermarket one. The numbers will tell you for sure.

--scott