Cat or No Cat

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    • Cat or No Cat

      Working on the exhaust on Not BlueJ and we need to build a custom exhaust to clear the 4 link. It's a 2002 and has the 2 pre cats in the header along with the O2 sensors. I don't need to mess with these. The third cat underneath is in the way. It doesn't have an O2 sensor after it so it shouldn't effect engine performance is I remove it.

      Am I wrong?

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    • Performance? Good question, it may be there for added back pressure. When my old TJ was 4 link rear i kept the cat there cause it was a 99 and was required. i bought a 6" round magnaflow muffler and did custom exhaust out the back

      That being said on a trail rig i would just put a dump after the cat and let her eat...

      Also on my current 03 i have a AFE long tube header to install that takes the system from 3 cats down to 1. can't wait to hear it.
    • Cat or No Cat

      I don't think you need it if no O2 sensors after it. I would still recommend a tail pipe, here's why. My first Jeep was a CJ8. The exhaust after the muffler fell off. I left it that way, with a half cab, it would pass imspection. Guess where the frame started to rust, yep, right above the end of my exhaust system. TJ's are getting a reputation like CJ's to have frame rust issues, it just seems like it is not taking as long for TJ's to have issues as it did CJ's. All the condensation built up and started sped up the rusting.
      A dump will also stir up more dust on a dry trail that a rear exit pipe. The guys behind you might appreciate that also.


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    • RE: Cat or No Cat

      pajeepman wrote:

      I don't think you need it if no O2 sensors after it. I would still recommend a tail pipe, here's why. My first Jeep was a CJ8. The exhaust after the muffler fell off. I left it that way, with a half cab, it would pass imspection. Guess where the frame started to rust, yep, right above the end of my exhaust system. TJ's are getting a reputation like CJ's to have frame rust issues, it just seems like it is not taking as long for TJ's to have issues as it did CJ's. All the condensation built up and started sped up the rusting.
      A dump will also stir up more dust on a dry trail that a rear exit pipe. The guys behind you might appreciate that also.


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      It's a trail only rig. It's getting dumped. Mine is and it doesn't make any difference with dust. Tires stir plenty up.

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    • Slowpoke wrote:

      The after-cat O2 sensors are only there to check to see if the cats are working by comparing O2 before and after the cats. They throw a code if the cats need to be replaced.
      They will also lean the mixture and make it run like crap. Sounds like the consensus is removing the last one won't matter since there is no O2 sensor after it.

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    • JKgray10 wrote:

      we recently replaced the cat on mine and added a muffler. It was a little too loud before hand. Picked a universal cat from pepboys. Installed with some flex pipe
      Looks good. You have a down stream O2 though so I could see it being needed. What spintech is that. I picked a 9000 series because of the size and going with a 2.5 in and 2.25 out to create a little back pressure like the cat that was there.

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    • I'd dump the 3rd cat, the front 2 do most of the work and since the rear isn't monitored with a sensor, you don't need it.
      Jerry / Whatevah
      2012 Rubicon - 2.5" AEV Dualsport XT lift, 315/70/17 MTZs, JCR Dagger winch bumper and engine skid, XRC Gen 2 rear bumper, Quadratec LED headlights, ACE side steps, ham radio with GPS tracker
      gone- Long-arm 2001 Cherokee on 35s