My catalytic converters have been clogged for awhile, and the o2 sensors need changed because of this.

What is it doing to my engine?

And gas mileage for that matter?

If i take out my converters and just put straight pipe with ports for the o2 sensors will that be ok?


  • In some jurisdictions, removing your catalytic converter would actually be illegal. May 1, 2015 at 9:16

1 Answer 1


If the catalytic convertor is truly plugged, you wouldn't be able to drive the vehicle, so this makes me wonder about the veracity of your statement. With a plugged cat, the back pressure created behind it will only let you rev the engine to around 1500-2000 rpm. I had to replace a set of heads on a pick-up truck for a guy because he continued to run the vehicle after the cat went bad. He drove it by keeping the gas pedal floored all the time. This cracked the head at the combustion chamber, which allowed coolant to leak into the cylinder. I gave the original diagnosis as a blown head gasket. This was before I tore it apart, found the cracked head, then discovered the cat was plugged, which was the original problem. This is a definite probability for any vehicle which gets run in the same manner.

Gas mileage will definitely be affected because you have to run the engine harder to overcome the back pressure.

You can take the convertors out and put in straight pipe. If this is an OBD-II system (which I assume it is because from your description it has "cats" and O2 sensors), you will never get the light off your dash without reprogramming your computer or installing O2 sims. In any state (or country) with emissions testing, this will fail. Better to just get new cats put in. If you don't have emissions testing and don't mind the dash light, there wouldn't be an issue with running it that way. You would, however, never know if there was another issue which popped up with the vehicle. This is a "do at your own risk" type of deal.

  • 1
    "you will never get the light off your dash without reprogramming your computer" There is such a thing as a sensor simulator. Aftermarket places sell these or you can make one yourself using a resistor.
    – maplemale
    Apr 30, 2015 at 19:30
  • @maplemale - Good point ... forgot all about sims. Thanks for keeping me straight! Added to the text. Apr 30, 2015 at 21:36
  • 1
    That's what the community is for. ;) I agree with your answer btw.
    – maplemale
    Apr 30, 2015 at 21:49
  • So i should have added more info. My check engine light has been on for some time. When I get a scan on it, it says check catalytic converters, it doesnt really say check o2 sensors. So I guess I was just assuming that they are clogged, but your answer enlightened me a little about what could actuall happen. But because I have left it go for about 2 years now it has started to leak exhaust in the cab or at least the smell when i turn the heat on. And the motor makes a sound pretty much like what ford usually makes but it seems to be getting worse, like louder. Its cats are so expensive.
    – Anthony
    May 3, 2015 at 14:19
  • Check the cats using the methods shown in this thread. If your cat(s) is/are good, I would suggest the issue is an exhaust leak after the upstream O2 sensors. May 3, 2015 at 14:30

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