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Discussion Starter #1 (Edited)
Ok on my 97 4.6 I had my whole exhaust done about a year ago, custom cat back with 2 1/4" duals with a midmounted magnaflow, ever since I purchased the car 2 years ago roughly once every 6 months (rarely) the engine light comes on for catalyst effiency below threshold bank 1, now it has moved to bank 2..... this vehicle regularly sees 25,000miles a year if not more so its obviously not a frequent occurance but the car is at about 109,XXXmiles currently, should I change out all the o2's or replace the cats? or both?

Just looking for feedback. Thanks.
 

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Only the second O2 sensors on each side monitor the cats. The cats on these cars do tend to fail at just over 100k, so I would put my money on your cats are dead and not your O2 sensors.
 

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Has it moved from Bank 1 to Bank 2 (meaning it is no longer on Bank 1) or is it now on both? I would look at the oxygen sensor data with a scanner and see how well it is switching before replacing anything.

Also, while the rear oxygen sensors are the only ones that monitor catalyst efficiency, the calculations are based off of data from the front ones, so the front ones can contribute to these kinds of problems.
 

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Discussion Starter #4
it occasionally throws either code P0420 or P0430 bank 1 below efficiency threshold , or bank 2 below efficiency threshold. Also I know that there are 2 sets, the front controls air fuel ratio and the rear only check efficiency.
 

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Discussion Starter #6
alright next paycheck I'll swap them for new ones
 

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it occasionally throws either code P0420 or P0430 bank 1 below efficiency threshold , or bank 2 below efficiency threshold. Also I know that there are 2 sets, the front controls air fuel ratio and the rear only check efficiency.

I got those same codes, would switch from one to the other. My car ran fine for about a year then started to ping, then ran a little rough. I got new cats and they havent came back, and its been 6 months since I had them replaced. Car runs smoothly now.
 
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