drago3431

Car: 97 2.8 A4(AFC) 5 speed 135k miles
Issue: Burned cat converter (driver side)

This is my second cat converter. The original factory one burned around 90k. I had it replaced with an aftermarket one. About 3 years later, the it is burned again. When I still had my factory burned cat on, I had no DTCs of any kind, passed all emissions (Illinois) and performance was not affected. So the dealer tells me to replace it without diagnosing the root cause of the failure. I had it replaced with an aftermarket and as I already mentioned, and it's burned again. The passenger side is fine - original one. My question is - what could be causing the cat to burn? I noticed at startup my mixture is very rich - I can smell gas from under the car (no gas smell from the engine bay), but ECU does not report rich mixture code. I had plugs and wires replaced about a year ago. Should I be looking at the injectors?
Thanks
Matt

AlwaysAudi

90K plus on your car if the factory O2 are still in there you "should" replace them. They generally don't throw a code until they are fairly bad. The upside, If your 02's are bad (but working) you are loosing MPG and performance. The way gas prices are the 02 sensors would pay for themselves in a couple years. In other words your O2 sensor is allowing you to mix rich the rich exhaust gas can and will deteriorate the cats. If your tail pipe is souty (sp?) I think the O2 sensors are a good place to start.

AlwaysAudi

What is your MPG like?

vovidzan

I had to replace cat converter after I replaced the head gasket. In my case, I think, the steam of leaking coolant destroyed it.

P.S The head gasket started to leak because the engine was overheating for a while and that was caused by a faulty thermostat which I replaced when I did my timing belt a year ago. So the bottom part is I should've kept my old thermostat

drago3431

Dealer replaced both O2 sensors on that side early 2004. As far as mileage, I get >24 mpg on average. Could they go bad in such a short time?