My car eats DEC catalytic convereters

[TCarlisle]

OK, so I know that BMW cats are very expensive, and if I spring the $1700 or whatever they last a lot longer. I know that an aftermarket cat is not going to last like a BMW cat.

However, my cats last only about a year. The car runs fine, doesn't throw codes, and I am very meticulate about maintenance. This is the situation for about 8-10 months after installing replacement DEC cats.

Then, I will geta P0420 code, usually when running the car with a light foot, or when it rains. I can clear the code, or just wait a few days and it goes away. This will happen about once every two weeks. As time goes on the code gets more frequent. Then, at about the year point, the cats start making a noise. Sounds like rocks inside rattling about.

The cats have no visual damage, and I am quite certain they haven't been bottomed out on speed bumps or anything, and I the only one that drives the car. The rubber mounts are fine.

Any suggestions? $350 a year to replace cats is not very cost effective. I though cats had to be gauranteed for up to three years by federal law. What gives?

[328 Power 04]

you can also find used cats at bmw salvage yards, but you'd have to be assured they're good... i'm still running original cats at around 170k miles... I get a catalytic converter insufficiency code every once in a while (once a year)

[TCarlisle]

Alright, so a little research tells me this is called catalyst fracture, and is typically caused by road debris, rocks, potholes, or broken exhaust hangers. My exhaust hangers are fine.

But in researching this, it seems like ther eare other reasons for cat failure. I still have the last set of cats that I removed last year in my backyard. Maybe I should saw them open to see if they are melted, carbon fouled, or just fractured?

thoguhts?

[TCarlisle]

OK, so I dug up this thread to update with the results of why this is happen.The result is that it is what we in the Air Force called Fm -- f^&king magic. Completely unexplainable and will forever remain a mystery.

Not long asfter I started this thread, I got a CE light and the code indicates cat efficiency too low. And soon after that I could hear the noise of something rattling inside the catalyst. So I figured the catalyst internals fractured, etc.

Well, one thing lead to another and life became a little demanding and I ended up blowing this problem off. Cleared the code and forgot about it. Didn't care about the embarassing noise. Just blew it off.

Well, the code would come back obviously, so I just kept clearing it. Then all of the sudden the noise was gone.So I figured the fractured internals of the cat blew out. But the code quit coming back too.

I can't even pinpoint when this problem went away, but it has been at least 6 months and 10K miles ago and since then I have not had one CE light. But yes the CE bulb does work. LOL.

Problem solved? I did nothing to fix it except ignore it. Maybe the problem created an additional problem in the downstream O2 sensor(s) in a way that the sensor no longer works but doesn't trigger a code about a failed O2 sensor?

I'll probably never know the answer to this because unless it throws a code and I can't pass inspection, I'm never going to look into it further. My state doesn't do an exhaust analysis on an OBD-II car, so I'll never know if the emissions are high.

[mt_goat]

"FM" huh...gota get me some of that. :D