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Unread 04-22-2010, 02:36 PM   #1
jdtuck91
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1993 XJ Cherokee 
 
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the cat

anybody know what would happen to a 91 4.0 if the cat was bypassed

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Unread 04-22-2010, 02:39 PM   #2
RebuildRookie
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1988 YJ Wrangler 
 
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fail emissions (if your required) in your state?

and I believe you have a O2 sensor back there as well. You would probably get fault codes for that. Otherwise mechanically probably no adverse effects.

Also, may be illegal in your state to remove the CAT, not for sure though.
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Unread 04-22-2010, 02:47 PM   #3
NHfireLJ
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Looked under my 94 the otherday..(bought last Nov) No cat! Runs fine.

For the record, I did not remove it... But when I replace the exhaust I will of course reinstall one...For emissions sake

Last edited by NHfireLJ; 04-22-2010 at 03:55 PM..
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Unread 04-22-2010, 03:01 PM   #4
QuantumYJ
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5...4...3...2...1...

Where's Rusty?
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Unread 04-22-2010, 03:39 PM   #5
beachedjeepyj
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Quote:
Originally Posted by QuantumYJ View Post
5...4...3...2...1...

Where's Rusty?
Haha i think he is on vacation.....
No more talk about removing the cat as it will result in the ban hammer.
http://www.jeepforum.com/forum/f180/cat-removal-302288/
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Unread 04-22-2010, 04:47 PM   #6
QBCoach
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What no cat??? On EARTH DAY...i'm telling Al Gore!
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Unread 04-22-2010, 07:26 PM   #7
ronfezz
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i passed emissions here in ct. without a cat, yet failed for its not being there. got a new one on there now no loss in power from my 4
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Unread 04-22-2010, 07:31 PM   #8
dadstoys2
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Hi flow cats are cheap and keep you legal. There is no major gain by removing it unless its bad anyway. But you will catch alot of crap by removing it from some due to polluting the enviroment for no reason. Its a jeep not a race car.
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Unread 04-22-2010, 08:35 PM   #9
provinT13
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Nothing. You will fail emissions, but the o2 sensor is before the cat so you don't have to worry about messing that up.

It's illegal to remove the cat under federal law, not saying your removing yours though, there is nothing wrong with asking a hypothetical question.
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Unread 04-22-2010, 08:54 PM   #10
4LarXedo4
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Why would you want to bypass your cat in the first place? There's many closed threads on cat removal and bypassing it, but why... if Your motor is stock then what is the point? There will be no performance gain at all, it's a Jeep not a racecar. Also as the other member touched on the topic of o2 sensors and is correct, Once your vehicle is up to operating temp in closed loop it utilizes the o2 sensor to determine the correct air/fuel mixture (after the exhaust has gone through the cat) for your engine to run properly and efficiently. I could go on for awhile on this but i'll save ya'll the boredom.
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Unread 04-22-2010, 09:14 PM   #11
MJMPC
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Quote:
Originally Posted by 4LarXedo4 View Post
Why would you want to bypass your cat in the first place? There's many closed threads on cat removal and bypassing it, but why... if Your motor is stock then what is the point? There will be no performance gain at all, it's a Jeep not a racecar. Also as the other member touched on the topic of o2 sensors and is correct, Once your vehicle is up to operating temp in closed loop it utilizes the o2 sensor to determine the correct air/fuel mixture (after the exhaust has gone through the cat) for your engine to run properly and efficiently. I could go on for awhile on this but i'll save ya'll the boredom.


On my 91 YJ the o2 sensor is BEFORE the cat and there is only one.
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Unread 04-22-2010, 09:25 PM   #12
4LarXedo4
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Quote:
Originally Posted by MJMPC View Post
On my 91 YJ the o2 sensor is BEFORE the cat and there is only one.
On vehicles with only one sensor before the cat are still used to determine pre-catalyst efficiency, Most vehicles with this setup (not sure on Jeep) the o2 sensor sends a signal to briefly lean the mixture in order to help the 'chemical process' and keep the exhaust somewhat 'clean'. That being the case, yes you could bypass the cat with no ill effects from a non existing post cat sensor, but once again, there will be no performance gain.
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Unread 04-22-2010, 10:09 PM   #13
dadstoys2
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I have an 87 with a webber and no computer at and still run the cat. Its cheap enough to just replace with a hiflow if you want less restriction.
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Unread 04-22-2010, 10:26 PM   #14
BlackRhino
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There is NO benefit to removing the cat. It does not restrict flow in any measurable way. Just leave it in and stay legal.
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Unread 04-22-2010, 10:26 PM   #15
K4KAS
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1994 YJ Wrangler 
 
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It is a $5000 fine to remove a known working cat. Not to mention a federal law.

That being said, mine didnt have one when I got it. I got tired of the raw fume smell. Then I looked under a realized there was no cat. I hat one put in by a cheapo muffler shop. No more fumes! It was really bad when the top was down or back window out. The Jeep seems to run smoother/better with it actually. It did change the tone of my exhaust note a bit. But the flowmaster never complained and it still sounds good.

With all this being said, I didnt get a check for $5000 when I put it back on!
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