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General E46 Forum
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Old 06-12-2011, 07:49 PM   #1
zeroyon
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Join Date: Dec 2010
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My Ride: 2001 BMW 325i
Bank 1 CAT Efficiency Question???

I threw a code for this in my car and was wondering which CAT it is? the one on the header or the one further down?? And if it is the on further on the exhaust can I replace it with a high flow CAT or just do a cat delete? Im going to get it tested to make sure that it is not just the O2 sensor first before I do anything...

Thanks for the help...
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Old 06-12-2011, 08:46 PM   #2
GDA
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That is probably a code that is thrown due to a downstream sensor from the real fault... lean or rich condition causing a O2 fault. Before you spend any significant amount of moeny replacing parts it would be well worth it to troubleshoot all upstream components first.

I'd make sure you have proper cylinder mixtures and balance by getting your data run from a Modis, GT1 or the like.
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Old 06-12-2011, 10:16 PM   #3
zeroyon
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Thanks, yeah I was going to get it checked out before I spent any kind of money. Any ideas though?
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Old 06-13-2011, 06:26 PM   #4
GDA
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IIWMCar... I'd spend an hour doing a once over in the following areas before hooking it up to a computer for some running diagnostics:

Pull all the coil boots and plugs and compare to see if one stands out (arcing, oil on plug boot, fouled plug, dark sooty plug etc)
Clean the ICV and DISA just as a precaution and to check all intake track area for air/intake boot leaks
Check valve cover gasket area while doing all the above to inspect for leaks/possible air leaks which could be a contributor to rich/lean running condition
Inspect CCV and hoses too for possible sources of vacuum leaks

Cat efficiency means you probably have a bank that is running a bit rich due to poor combusiton or a vacuum/intake tract leak and then the cat is not able to help perform a complete burn... therefore, giving another reading at the second cat with HC, CO leftover....

Just my .02 based on the info you posted
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