996 Misfire and failing Catalytic Converter

My 2002 Targa is misfiring. The dealer says it needs a new catalytic converter (CC) for bank #1. There are two code, one indicating a below par CC for bank #1 and a malfunctioning fuel tank pressure sensor. The misfire comes on at the same rpm each time, 4400 rpm, and the engine shuts down like it had hit the rev limiter. I don�t doubt the codes, but for the misfire to occur at the same rpm each time suggests something else may be coming into the mix. Does some function, like camshaft timing change at 4400 rpm? If I down shift so the engine spins higher than 4400 rpm there is absolutely no power. I have 86K miles and I can drive the car below 4400 rpm with no apparent trouble except the car has started stalling occasionally while idling and it takes about 20 seconds of cranking with my foot on the gas before it starts. I�ll be buying an aftermarket CC soon. At $2600 the dealer can keep their OEM cat. Has anyone purchased a CC from the Catalytic Converter Warehouse? They have a replacement that looks like it fits one side only � not sure which side yet. I want a CC that will last, not one that I�ll have to change every few years. I�m a little hesitant to buy a performance CC. I�m concerned they�ll lose their efficiency too fast. Any help is appreciated.

Coil pack failing?

I had the exact same problem on my car and it was frustrating because I threw money into it and couldn't figure it out. New coils, spark plugs, O2 sensors, and even the MAF sensor. My car would function perfectly until it hit around 5k RPM then it would misfire. It started out as an intermittent issue but eventually became very consistent. Finally I left it at the dealer and they disconnected the cats and found the problem. I personally went with the Fabspeed sport x-pipe cats and love them. BUT they do change the tone of the exhaust into a much more sporty sound. If you're ok with that then it's a reasonably priced choice. Otherwise I'm not sure of the reliability. As for a performance exhaust failing too quickly. Well in all of my research I've only seen posts about stock cats failing, I've not seen any with aftermarket failures yet. Not to say it won't happen but at least no one I've seen has written about it.

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There are no misfire error codes? Is that correct? If so, the symptom is not a misfire, at least by the DME's definitiion. The DME keeps close tabs on the cam timing and if this was not right there would be one or more error codes associated with this. I'm not clear on that fuel tank pressure sensor issue. A couple of things come to mind: If this mailfunction was causing the fuel tank pressure to climb (or fall) from its normal range this could result in too much or too little fuel or fuel pressure. Now the DME is not supposed to record a misfire if the tank's level is too low but if the tank's level is ok, but there was an over/under pressure situation? But still if I read you correctly there was no specific or general misfire error codes logged? You might consider having this fuel tank pressure sensor problem addressed just on the outside chance it is playing a role in the engine's behavior. That the behavior appears at the same rpms consistently does to me (I'm not a pro tech though) point to a converter. What happens is the converter has likely suffered a mechanical failure which compromises its function and the error code of the converter performing below par (P0420 or P0430 are two that come to mind) conveys that. The engine's inability to run above 4400 rpm is probably due to the converter interfering with the proper flow of exhaust gases out the exhaust. The engine cant' develop full hp/torque because it simply can't flow sufficient air (the engine is just an air pump in some respects). However, I'm not sure I'd replace a converter without a higher degree of confidence the converter needed replacing. They are expensive enough one wants to be sure. The problem is it is probably not cheap to obtain this higher degree of confidence in the converter being at fault. One possible course of action would be to remove the suspected converter and shake it to determine if the metal matrix was intact and secure. "Stuff" might come out if the converter was upended, too. Also, a visual inspection looking into the converter from both ends might spot signs of obvious mechanical failure. What your after market options are regarding converter replacement I have no direct and very little indirect experience. Sincerely, Macster.

Does it misfire and then start running again ok after a day or two? I went through this for the last two years. Replaced coils, plugs, lift controller pressure regulator, the works. Finally, we got an error code that indicated lifters were sticking on the number 4 cylinder. Replaced both lifters, and no more misfires. Unfortunately, over the two years, it took a toll on my right cat and now I get a repeated error code 430. Need a new right cat. Dang. I am living with it for the time being as the car is running fine and the smog test around here is no problem. Let me know if you get the new cat or otherwise if this suggestion of a stuck lifter helps. Good luck.

Thanks for your suggestions. I'll read the error codes again just to make sure there is nothing new. I expect I'll remove the cats to see if there is any rattling; the dealer says they are but I'm not sure how they came to that conclusion with only one hour of investigation. If I need to replace one (code shows only bank one at this time) or both cats, I'll need to decide between the Fabspeed X-pipe setup and the Cat Converter Warehouse cat. I replaced the plugs and coils about 10K mi ago although that doesn't guarantee the problem doesn't reside there. One mystery is that the engine cuts out completely if I.down shift to an RPM above 4400. fpena944, The only noise I don't like in my Targa is the road noise from the tires. I use my car as a daily driver, I don't really want to hear the engine droning at 5:30 in the morning on my way to work. Right now I can't hear the engine while cruising down the interstate. When I hit the gas the sound is sweet so if the X-pipe doesn't increase noise at steady speeds but does add a more sporty sound on accelerating I'd be fine with it. How would you describe its aural behavior? Folks - Thanks again for the benefit of your experience and suggestions.

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PaulJB, You may want to PM a member by the name of Riad here on the forum. He can give you a better indication of what the x-pipe will sound like with a stock exhaust. Mine is loud because I have the sport exhaust. But from what he had told me the sound with the stock exhaust and x-pipe is perfect. Granted, it is mostly loud when accelerating as at low RPM or while cruising it's really not that noticeable. But if you push the throttle there is quite a difference. For me when leaving the house at 5am I shift into 2nd as soon as I can to keep the noise down.

This behavior is indicative of a plugged cat. Sometimes you can remove the rear O2 sensor and see the degraded catalyst material in the hole. You may need to remove the cat to see for sure though.

You can buy factory OEM Porsche cats for $1229.59 each. http://www.porscheoemparts.com/parts...HAUST%20SYSTEM

fpena944 - thanks for the info. It seems like the change in exhaust sound with the Fabspeed cats would probably be acceptable. Where can I get factory cats for $1229? Thanks for the help folks.