P0420 with new walker catalytic converts

Any suggestions on what to try next- at 197K I replaced both 02 sensors, and the charcoal canister, along with two new walker cats. It has run for 5000 miles with no issues and no codes. Last week the check engine light came on - P0420. I cleaned the Mass Airflow sensor and the code came back in a day. What would cause 2 cats to go bad after ~5000 miles?

 

Aftermarket cats are junk. That said, return them while they are under warranty.

 

Walker cats are good quality, not as good as oem but still a good aftermarket. Did you make sure to get the California grade or California emissions cats? If not then that could be your issue. If you did get the correct ones then maybe there is an underlying issue that hasn't been addressed yet, the same issue that caused your old cats to go bad. Any other codes being thrown?

 

Check the flange between the post cat 02 sensor and the cat. Even a pin hole leak in that gasket will throw the code. Muffler shop tried telling me I needed new cat at the tune of $1500 installed. I said "just double up that flange seal and I'll try that". Code went away for about two months. It's back and I rechecked....another leak at my flange. Seems the 13 yo flange is so soft, it wont hold the pressure applied from the tightening of the bolts. he heat and cool of engine temps causes it to loosen back up and oila.... p0420. I will rectify this by having flanges cut off both pipes and re-welding new flanges to create a good seal. Good luck.

 

Im curious if you could just weld the flange together/ shut?

I was in a similar situation recently and thought about welding the flanges together instead of dealing with stripped bolts.

 

I don't see why you couldn't. Same as just welding in a a solid pipe to replace the flange. The only reason the flange is there is for ease of replacement I would think.

 

Thanks for the suggestions! I'll check for leaks, and I don't have the Cali emissions cat.
I did get it to pass emissions today, I dumped in 2 bottles of Cat Clean by mr. Gasket and drove it for 50 miles and no light. On my odb tester my cat is still in not ready, everything else tests out ok

 

Nice job on getting it to pass. Hopefully the code will stay away.

I have the California Grade cats which are supposed to be the same as the California emissions cats except they don't have the stamp of approval by the commission that regulates emissions in California. I have about 1k on my new cats and I'm praying they last a good while since I dropped $550 for magnaflow cats. Next time I'm going with the Cali Grade walker cats from rock auto.

 

Giddy up!

 

try diagnosing the problem before you throw parts at it

both cats wont go bad usually the front does 80% of the work and is usually the one to fail.

did you check the muffler bearings yet