What causes a Catalytic Converter to go bad?
My ses light went on last week so I made an appointment and took the car in yesterday. I get a call from the dealer later in the day and I'm told that the reason for the ses light is due to my after market exhaust. I have had a Magnaflow exhaust on the car for 3 years. I also have the Mini Mania header with Cat. The only other time the ses light went on it was apparently due to the o2 sensor being bad and once it was replaced the light went away. I told the service advisor this and asked if they could just replace the sensor again. He says that this time the code is not saying the sensor is bad it is saying that the catalytic converter is shot. So back to my original question...what causes the catalytic converter to go bad? And what are my options here?

Thanks,

Ken

 

is your mania header with the mania cat? if so, I think the mania cats are bad. they have since stopped selling their headers because of this.

edit: to answer your question, yes I believe the cat can be trashed via a free flow exhaust system coupled with improper tuning. I believe this happened to Dr Obnxs in a fairly short period of time (2-3 weeks). Seeing as how you have had your Magnaflow for a few years, I'm more inclined to think you have a bad cat since the mania header does have a recent history of bad cats.

 

I'm not sure I see how the cat would be bad because of the exhaust, since the magnaflow is all after the cat? I would be more inclined to say it had something to do with the header

 

That was my point, the cat was part of the mania header.

But I have also heard of aftermarket cats getting cooked via a free flow aftermarket exhaust not tuned for that exhaust. hasn't happened to me but I know others can attest to it.

 

that going with header and free flow exhaust without getting more advanced timing can result in more buring in the header, and increased exhaust temps. I ran a Magnaflow cat on an OBX header with a custom built 2.5" free flow single side exhaust, and lost the cat in less than a month. I also had the HAI and a 63mm TB on the car. EGT were scary high until I got a better tune.

But this is just a theory, and if true I would also expect those running ported heads, headers and exhaust to see something similar, but I haven't heard of anyone running that combo and not tuning for it. So it's all up in the air.

FWIW.....

Matt

 

 

But there was something else going on with my car. The cat didn't cook at WOT, it was at part throttle, with the flat spot. A/F ratios would go high, and EGTs would shoot up. Cruising on the freeway is what did it, so I've got more thinking to do!

Matt

 

WellI know the Computer doesn't have a code saying the Cat is shot was it a post CAT O2 malfunction? do you know what code the dealer got and then who they determined the CAT to be the source? This is where my first concern is, make sure the CAT is where your issue is as if it was simply a code there are several factors involved in setting off each one.

 

Aftermarket header/cat do go bad but I wouldn't necessarily take one opinion for a diagnosis. Get a second opinion.

That said, my Miltek header's cat did go bad (came loose) and Stratmosphere promptly replaced it without charge It was do to an early design flaw...

 

The ECU uses fuel trim to correct AFR. The cat-back exhaust might have improved scavenging and thus the ECU will correct the trim. However, none of the exhausts on the market for the MINI use proper exhaust tuning to increase scavenging, so AFR changes based on that are moot. That said, the OBDII is usually spot-on with its diagnostics, so when it says the cat is bad, it usually is. This is probably because your WOT mapping is crap, or the catalytic converter substrate is crap. Get Mania to replace it.

 

So, the cat is getting HOT? A bad cat is a plugged cat. As in other posts on this thread, your Mania cat must be flawed. Everything behind the cat would have little or no effect.

To answer your question, the cat breakes down due to additives that plug the cerimac ( that is why you must use no lead gas, not that you can buy any leaded gas at your local gas station...). When the ceramic gets hot enough it degrades, plugging the exhaust passage.

 

Have you used any "Octane Booster"?


A couple of years ago I was at a MINI car meet, where there was a trailer full of "FREE for the taking" Octane booster. Of course I took several boxes. In researching the Octane booster I learned that the Manganese in it could damage the CAT and the O2 Sensors. I am now burning that stuff up in my 1978 Mini so as not to risk the cats in my current cars.

J. D.

 

The pre-cat O2 sensor on the MiniMania header is about 5 inches farther downstream than the OEM position. I would not think so, but could this
make a difference? Also, the post-cat O2 sensor is closer to the cat than the OEM position. By the way, I believe that the Mania header has a Magnaflow cat.

 

Thanks for the replies. The paperwork from the dealer did not identify what codes were logged. It simply said: "Customer reports that ses light is on. Fault for catalytic converter efficiency present. Car has aftermarket exhaust sysytem. Not warranty".

No I haven't used any Octane Booster but thanks for that tip.

Mini Mania did in fact replace the header due to the cat once before (about 8K miles ago) so it looks like I'll be after them again, but somebody has said they don't do headers anymore so that will be interesting.

Ken

 

I believe they will be (if not already) offering a header/cat, but just not the same one they had before, due to all the issues.

I recently tried to purchase the mania header but they told me they were not selling them any more. They did offer to sell me a used header sans CAT for a reduced price, but I decided to go with another setup.