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Which have you had fail more often?

  • Catalytic Converters

    Votes: 4 23.5%
  • Rear O2 Sensors

    Votes: 10 58.8%
  • Equal Failure Rate

    Votes: 3 17.6%

  • Total voters
    17
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Discussion Starter #1
Simple question: Which have you had fail more often on your vehicles (not necessarily MN12, but if it it mainly not for, please so state.) the catalytic converters or the rear Oxygen Sensors?
 

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where's the option "I have no clue"? :D
 

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rear O2 sensors? what are those?!?! Oh you mean those metal things that are used to plug up the holes behind my High Flow cats??
 

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If you are getting a cat below efficiency code, then the failure is the cats, not the rear O2s. In order to throw that code, the ECM needs to see voltage varying between 100 and 900mV. This will only happen if the cats aren't cleaning up the exhaust. If the rear O2s were to fail, you would get a different code. Most of the time when O2 sensors fail, it is either the heater that fails, or the response time slows down so it is switching much slower. In the rear position, this slower response time would actually make it less likely to throw the cat below efficiency code because if the cat were just marginally failing, it might not pick up the minute changes. If the heater failed, it would throw a different code for the heater inop. The only way for a failed O2 sensor to cause a cat below efficiency code would be for it to fail in such a way that the voltage it was putting out was constantly varying, and I have never seen that happen.
 

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if your getting that code and you've never had a headgasket pop than replace them both. On the other hand if you have had a headgasket let go on your bird than its more than likely the O2's only.
 

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Easy to fix either problem. Get rid of your cats and have your tuner shut off the rear o2 function in your ECM ;) That is unless your in a state that does emission testing.
 

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I've only ever owned 2 vehicles with rear sensors so my result should probably be weighted.... I'm still driving OEM cats and sensors in both. One of them is in the garage waiting for new cats and sensors (as part of a larger plan) at about 180k.
 

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it's not good to delete your cats, your motor needs the back pressure
No motor ever needs backpressure in the exhaust! This is nothing short of a complete fabrication, and any backpressure at all will cause a major drop in power! I really wish people would stop propagating this misinformation. Ideally what you want is a little bit of vacuum in the exhaust when the valves open, but definitely not pressure. This vacuum is created by the speed of the exhaust gasses that are exiting the exhaust. Running too big an exhaust will reduce the exhaust gas velocity, which will effectively increase the pressure in the exhaust, which is what hurts low end torque.

With that said, running without cats will not hurt your power or torque at all. Cars did just fine without them for 50+ years. What will hurt your power is just punching the catalyst out and leaving the big hollow empty space in there. As soon as the exhaust hits that wide open area, the velocity drops like a rock, and that will hurt your low end torque. However if you were to cut the cats out and run straight pipe in their place, there would be very little change in power, but to the extent that there was any difference, it would increase power across the board, not decrease it.

Now please stop telling people that engines need backpressure in the exhaust!
 
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