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Can I leave the 3rd cat off my system? if I do will i get any performance gains. How about if i change the muffler to a borla as well? Oh, i need a front drive shaft pretty bad so if you know of one...
 

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I don't know what kind of laws you have there so I won't get into that or the legality of removing it. Mine isn't tested so I've done a bunch of "seat of pants" testing on the exhaust. There is a definite increase in power/performance/driveability/mileage by removing your factory muffler and 3rd cat, and replacing with simply a piece of strait pipe and high flow muffler. It's a bit louder overall, but definitely more performance all around and better mileage. I recently replaced my entire cat setup due to my front upper being clogged and re-installed all OE cat equipment. I now have the 3rd cat with high flow spintech muffler. After running and testing this, I will be removing the 3rd cat again as there is a definite noticeable drop in performance and mileage with the 3rd cat in. It's not as substantial as removing both the factory muffler and 3rd cat and running only a high-flow muffler, but there is a definite difference. I've lost a bit of power and a little mileage as well. Not sure yet if I want to totally eliminate the 3rd, or pull it and clean it out/rod it out if you will, then reinstall the can itself to see if that deadens the sound any or what. Haven't decided yet but something will be done before too long. May consider putting in something like a high-flow cheap muffler in front of the spintech, cherry bomb, something else similar to see what that does to performance and sound levels. I really prefer a quiet rig all around. If I can't get the performance out of it I know it has, I'll deal with sound. It's not bad or harsh by any means, I just really like them as quiet as possible around town and especially on the trail.

Best of Luck,

Mike
 

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The only performance gain I got losing the third cat was because it was plugged. I didn't get any better than stock mileage and power (power determined by fifth gear hill ascent on a road near my house).
I put on a magnaflow muffler (straight through design) and noticed no improvement, but also it's hardly louder than stock.
The top two cats disintegrated on their own, this time power and mileage went down. Probably due to having two large can shaped turbulence generators (the stock cat housings) at the manifold, right where you would prefer to maintain exhaust velocity. Still sounds very quiet, even with a straight exhaust and minimal muffler.
If required by inspection in your state, I would maintain the cat. Otherwise, I wouldn't spend the money to replace it and wouldn't waste the time to knock it out.
But as with '05TJLWBRUBY's experience, YMMV.
 

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Jeepless in PA
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If your state requires a third cat, I would break out the innards. It is not doing anything :D
 

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I wonder without the guts in that cat or also in the other two, what effect that has on the O2 sensors? They determine how much fuel and air it needs correct.
 

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I read here the 3rd cat is not monitored so its loos sould not set codes, the first two cats are monitored and O2 sensors will trigger codes if they don't get the right readings or if a wire gets cut by a tree.


john
 

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What's weird about Heck's experience is that his remained quiet for the whole thing. With my cat plugged-it got noticeably louder and a bad sound overall. I've experienced more driveability issues, that sound is getting bad again and louder and it's running more rough than it has been. Still tripping misfire codes too, which with everything else is dumping more fuel to #2 and consequently from what I've read, too rich or dumping too much fuel is the fastest way to kill the cats. In addition to a crapped out engine, I'm starting to think my front upper is going out again... Will NOT be replacing them again. Mileage has been in the crapper for a while now. Maybe it's getting close to time to start thinking seriously about the engine swap...

Best of Luck,

Mike
 

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I've replaced mine twice now. Once under the 80,000 mile emissions warranty. Then again at 93,000. Those cats they replaced only lasted 13,000 miles. I went with a off brand, didn't want to pay for the same ones again.
 

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I've replaced mine twice now. Once under the 80,000 mile emissions warranty. Then again at 93,000. Those cats they replaced only lasted 13,000 miles. I went with a off brand, didn't want to pay for the same ones again.
 

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Topless Rubi said:
I read here the 3rd cat is not monitored so its loos sould not set codes, the first two cats are monitored and O2 sensors will trigger codes if they don't get the right readings or if a wire gets cut by a tree.


john
correct, the big cat isn't monitored. as for legality it doesn't matter where in the u.s. you live, it's illegal to remove any of the cats on the jeep. it's not a state law that prevents it, it's a federal one. that being said, it's done all the time :rotflmao:
 

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I can also say that all cats are gone on my jeep (not removed, the ceramic substrate disintigrated due to vibration). After 6 months and 8000 miles, I have yet to see a code.
 

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Here is one of DoctorD's experiences with cats.
 

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heck said:
I can also say that all cats are gone on my jeep (not removed, the ceramic substrate disintigrated due to vibration). After 6 months and 8000 miles, I have yet to see a code.
yea i hear metal rods vibrating in them tends to screw things up :lildevil:
 

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it would keep the overall exhaust hotter, which should burn up a little more of the leftover gases....but it'd be more trouble than it's worth. with properly functioning emissions setup the jeeps qualify as ulev vehicles...at least my 06 is labeled as such.
 

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Ultra Low Emission Vehicle.
An emission standard established by the gov't.
 
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