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Blazinski
09-30-2014, 09:30 PM
Hey everyone,
New here and I have a few questions. I have 05 a6 4.2, I have a cel coming back with a bad cat, I live in rio rancho nm and don't have emission tests here. I'm thinking of removing the cats and just putting pipes to fill the space. Is their anything else I should do or is recommended to do besides just removing the cats. My car has three cylinders misfiring right now and I take it's from the bad cat, now removing the cats will that fix my cylinder missfires? Any help or direction on how to handle situation would be appreciated. Thanks guys.

Tarrant
10-01-2014, 06:46 AM
The three cylinder misfires probably caused the bad cats, not the other way around. You can remove the Cats but eventually you are going to have to deal with those misfires still. Check your plugs, cables, coils and injectors.

v8a6
10-01-2014, 06:55 AM
And, you will get other errors in the ECU when you remove your cats. So, if you plan to do that, also plan on getting a custom ECU tune to get rid of the resulting errors.

If anything, I would install high flow cats in place of the bad ones. But, youll still get the same errors, and will need an ECU tune. Once you ditch the factory cats and add a tune, you should get a nice jump in power.

FL C6 Avant
10-01-2014, 07:49 AM
The three cylinder misfires probably caused the bad cats, not the other way around. You can remove the Cats but eventually you are going to have to deal with those misfires still. Check your plugs, cables, coils and injectors.
+1
You may have melted down the cat and have significant backflow. But something caused the cat to clog.
Fix the problem, then will have to also deal with the cat.
Check your fuel trims and o2 sensors.
A lying sensor can tell the computer to go rich rich rich rich until you are fubar

Blazinski
10-02-2014, 07:26 PM
Thanks guys for the feedback. My plans were to delete cats then give it a complete tune up. New wires, mass airflow sensor, spark plugs etc... Is their a universal replacement recommended to install by cutting old cats out and welding in universal cats. Or do i have to replace them from the manifold back as I'm being told. I was also planning on changing my exhaust to magnaflows also. Thanks.

v8a6
10-02-2014, 07:43 PM
I dont think there is any universal cat that is recommended. Since your state does not require a catalytic by law, then it may be easier to completely delete them.

If you choose to install a universal, then you would be best to consult with your exhaust shop to see what they recommend. I have used the Magnaflow 59959 Metalic cats on two of my cars, and they seem to work well. Just make sure you go with a metallic, not ceramic. A 200 or 300 cell should work fine. HJS are top of the line, but very expensive.

I am not familiar with the location of the cats on the 4.2. On the S6 v10, there are four cats (two per side) and two of them require an engine pull for repair/replacement.
http://img560.imageshack.us/img560/6355/s6motor.jpg

If the 4.2 is the same, then I would recommend they be replaced with a single downstream cat per side, that can be accessed without an engine pull. That will make them easier to access if you ever have to replace them again, plus, there will be a lot less heat buildup near the engine, compared to the restrictive OEM cats.

You will also need a tune after to account for the higher flow that the ECU will be seeing.