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Discussion Starter #1
Hi all, This is my first post here but this site has helped me many times thanks to everyone.

So, my check engine light is on and I'm getting P0430 and P0420. I've pretty much narrowed it down to my cats being bad. I had some misfire problems previously and I definitely have reduced horsepower on the highway. From reading hear and elsewhere it seems that those issues point to bad/clogged cats.

I have 2 options as of now, but haven't quite decided what to do yet and I'd like to hear your input.

Option 1 is to buy a new y pipe. I don't really want to spend $300-$400 and I'm in Mass so I do not have to pass emissions.

Option 2 is to put a straight pipe through the cats. I've read that this will help with horsepower and fuel economy, plus it's essentially free so this is what I'm leaning towards. I know I would have to trick the O2 sensors so the codes would go away. I was planning on just cutting the three wires going to the sensor and putting a voltage divider on it. Does anybody know what the sensor voltage would be with a new cat?

Also could someone clarify as to what exactly the flow of the exhaust system is. I've been going by this diagram http://images.wrenchead.com/smartpages/partinfo_resize/MER/100373.jpg which seems to show a third cat after the y pipe. Is there 3 cats? Could this one be the problem?

Any input is appreciated. I'll be removing the y pipe in a couple days, so I can post back with some more info. Thanks.
 

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Discussion Starter #2
More Problems

To add to the problems, the car lost power on the highway. I couldln't accelerate and ending up going about 25 mhp most of the way. Im now getting codes P0411 and a cylinder 1 misfire in addition to the cat codes. Anybody have suggestions?
 

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Sounds like your exhaust is close to being completely clogged.

Yes, you do have a 3rd cat. Personally I don't like the idea of running without any cats, so what I would do is spend the money to replace the Y-pipe, and if the 3rd cat is clogged then just straight pipe that one. The 3rd cat is unmonitored, so the computer won't notice, but it will if you delete the upstream cats. "Fooling" the O2 sensors is harder than just providing a set voltage. It has to go from 0.1 to 0.9 and cross 0.45 periodically just like the real O2 sensor would. You would have to buy an O2 sensor simulator, and sometimes they don't even work. See here: eBay Guides - Truth about O2 simulators

So honestly I think it would be simpler to just replace the y-pipe with new cats rather than spending the time to have your existing exhaust modified and trying to fool the computer.

I should also mention that catalyst failure is almost always the result of an engine problem (misfire, bad head gasket, leaking rings, etc). So you must fix the root cause otherwise the news cats will also go bad. Your misfire might just be a result of high backpressure, or you might actually have a problem with #1 coil or spark plug.
 
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