glowing red hot cat. converter

[kimi]

this is a 2000 A6 ATQ 2.8L. i had to replace the right side converter. within 15 days i have had to replace two different cats from diferent manufactures (bosal and catco) cuz the cats get glowing red hot and throw out all these codes P0421, P1393,P0300,and many others. i have had to change the O2 sensor but the problem just wont go away. i must say that both this cats, although they do fit, they look way smaller, especialy the anterior cat, in size than the original. but the customers service claim they are ok for this car. at this point after replacing and re-replaceing this dam thing i am not sure what to do next. i have odered a new one from eastern cat. which looks identical to the original, hoping it will work as i have had no problems with it after haven used it 3 months ago for the left side. has anyone any ideas concerning this. i am freaking out. thanx guys

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[chefro]

You should take your car to an Audi dealer or an Indie that does know Audis.
It sounds like the muffler shop you took the car to does not use the right cats, but even though smaller they shouldn't get glowing red as new.
In any event, you may have an underlying fuel problem.

It's NOT clogged (yet) and it's not "doing it's job." A cat normally gets very hot when in use, but NOT GLOWING hot.
Something is causing raw unburned fuel to be sent down the exhaust pipe where the cat "burns" this fuel. The cat is designed to burn the tiny amount of unburned fuel that comes from a normal engine. Now, if you pour excessive hydrocarbons (fuel) in the exhaust, the cat will burn that too and since it's burning too much fuel it glows red hot. This won't last very long, this is very damaging to the cat. The catalyst can get hot enough to melt. And that won't take long! And when it melts, then you will have a blob of molten metal blocking the exhaust pipe (now it's clogged!) and the engine will stop operating. At that point, the only fix is replacement of the catalytic converter.

However, if you find and fix the problem now you can avoid that expense. You have to find why raw fuel is going through the engine. The most common reason would be a bad spark plug or bad spark plug wire. If the spark doesn't work, there is no "combustion" in that cylinder and the raw unburned fuel goes out the exhaust pipe.
Other problems could be a bad carburetor mixture, bad computer causing overly rich mixture, clogged fuel injectors, even bad /burnt valves and/or rings but heck lets not think about that.
But get an expert to look at it NOW and don't drive it any more till it's fixed, or that cat will melt and then you'll be in deep do do.
Good luck.

[Midniteoyl]

You have an underlying problem..