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Old 12-10-2010, 11:26 AM   #1
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Removing a Cat

I am about to replace my exhaust manifold ( THree Cracks). IN a 2003 2.4L, and i thought about removing the catalytic converter. is there any difference in driving with one off? any good things about removing. .and i would have it so if i got called to have inspection i could slip the pipe back on.
Pros and Cons of doing this
THanks

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Old 12-10-2010, 11:31 AM   #2
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you'll find only bad things about removing the cat.

engine will run like crap cause the computer will freak out and throw CEL's. and removing the cat is illegal.

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Old 12-10-2010, 11:47 AM   #3
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I recently took mine off because it had holes in it..(was getting a odd noise when decelerating) and replaced it with a shunt until I can get a new Cat....

I've noticed that my gas mileage is a bit better, acceleration is better and I get a bit more power. Note that this may be because I got rid of my messed up cat...not sure how if removing a functioning cat will yield same results.

inb4 illegal-it's bad for the the planet.

Hope that helps
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Old 12-10-2010, 12:02 PM   #4
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I'm running a dynomax muffler and no cat on my 2.5. No cat because mine was bad and I just haven't got back to installing a new one. Mines a YJ so I don't throw codes or anything. I noticed a little more power but that's probably just because the old cat failed.
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Old 12-10-2010, 12:15 PM   #5
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Thought Id get some advice about keeping a stray cat out of my jeep. nope. and apparently keeping a stray cat out of my jeep is illegal! WHAT!?!?
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Old 12-10-2010, 12:33 PM   #6
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Originally Posted by chensley View Post
I recently took mine off because it had holes in it..(was getting a odd noise when decelerating) and replaced it with a shunt until I can get a new Cat....

I've noticed that my gas mileage is a bit better, acceleration is better and I get a bit more power. Note that this may be because I got rid of my messed up cat...not sure how if removing a functioning cat will yield same results.

inb4 illegal-it's bad for the the planet.

Hope that helps
-c-
i'm going to assume this applies to the YJ in your avatar. With your OBDI Jeep, your computer won't have a heart attack. But with the newer OBDII TJ's, it controls fuel delivery and based on O2 sensors. There is a pre-and post-cat O2 sensor. The computer adjusts the A/F ratio based on how much O2 is in the exhaust from the pre-cat O2 sensor...but it will monitor the cat's health with the post-O2 sensor. If the cat is running hot, the engine will dump more fuel in to cool the cat, if its running cool, it will trim out some fuel to heat it up. The O2 sensors also look for a specific O2 differential between the pre-and post-cat sensors, which indicate the cats are working properly. The OBDII expects these voltage values to stay within a specific range. If they don't, it trips a CEL. If the cat is missing & the O2 sensors aren't in place, the computer will continually try to heat up the non-existant cat...so it can change fuel delivery to try to accomplish this...meaning your engine will run like crap and you'll have a CEL.
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Old 01-22-2011, 12:58 AM   #7
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i'm going to assume this applies to the YJ in your avatar. With your OBDI Jeep, your computer won't have a heart attack. But with the newer OBDII TJ's, it controls fuel delivery and based on O2 sensors. There is a pre-and post-cat O2 sensor. The computer adjusts the A/F ratio based on how much O2 is in the exhaust from the pre-cat O2 sensor...but it will monitor the cat's health with the post-O2 sensor. If the cat is running hot, the engine will dump more fuel in to cool the cat, if its running cool, it will trim out some fuel to heat it up. The O2 sensors also look for a specific O2 differential between the pre-and post-cat sensors, which indicate the cats are working properly. The OBDII expects these voltage values to stay within a specific range. If they don't, it trips a CEL. If the cat is missing & the O2 sensors aren't in place, the computer will continually try to heat up the non-existant cat...so it can change fuel delivery to try to accomplish this...meaning your engine will run like crap and you'll have a CEL.
Can these sensors be bridged to bypass the OBC? As I understand it, the OBC on the earlier 1990 models did 3 checks.
1) Air mass
2) Oil
3) CAT

Is this true? and can this be done?
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Old 01-22-2011, 01:16 AM   #8
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They make a thing called an O2 sim for the O2 sensor that is affected when the cat is removed...that basically tricks the computer into thinking the O2 sensor is functioning correctly, however, as mentioned...it's illegal to run with no cat on the streets.

I don't think you'll see any power increases really...but I've heard it does deepen the exhaust tone considerably.
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Old 01-22-2011, 02:32 AM   #9
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But i looked under my 01 and i dont seem to see any sensors like on other cars that are aftr the cat. Doesnt that mean it wont read codes?
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Old 01-22-2011, 09:08 AM   #10
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you'll find only bad things about removing the cat.

engine will run like crap cause the computer will freak out and throw CEL's. and removing the cat is illegal.

I have had mine removed from a '97 4.0L for over ten (10) years now with NO problems at all ! Even past smog check last month !
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Old 01-22-2011, 10:11 AM   #11
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I also removed my cat on 97 4.0L with no problems. Just remove CEL bulb.
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Old 01-22-2011, 10:53 AM   #12
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I know running without a CAT is like a $2500 fine or so I was told at the shop.
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Old 01-22-2011, 10:57 AM   #13
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Thought Id get some advice about keeping a stray cat out of my jeep. nope. and apparently keeping a stray cat out of my jeep is illegal! WHAT!?!?
Bring the stray cat to the local chinese restaurant. They specialize in them.
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Old 01-22-2011, 11:34 AM   #14
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Tastes like chicken.... mmmmmmmmmmm
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Old 01-22-2011, 11:34 AM   #15
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What about Jeeps with the pre-mini cats, would removing them cause any harm or give any benefits? They are only there for California emissions IIRC
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Old 01-22-2011, 12:42 PM   #16
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What about Jeeps with the pre-mini cats, would removing them cause any harm or give any benefits? They are only there for California emissions IIRC
Are you in California. Either way the computer knows it there and may spit codes.
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Old 01-22-2011, 12:49 PM   #17
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on my 02 it has the 2 pre-cats (right after the manifolds) and another large one under the skid plate. the 2 pre-cats have the 02 sensors before and after them, the cat under the skid did not have a 02 sensor behind it.

The only one you could remove (not saying legally) would be the one under the skid plate because there is not an o2 sensor after it. Like it has been several times before me:

IT IS ILLEGAL TO REMOVE A CATALYTIC CONVERTOR!!!!
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Old 01-22-2011, 12:57 PM   #18
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It is Illegal to take that 'lill tag off your matress !
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Old 01-22-2011, 01:03 PM   #19
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you will not pass inspection without it
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Old 01-22-2011, 02:04 PM   #20
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It is Illegal to take that 'lill tag off your matress !
And your PILLOW!
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Old 01-22-2011, 02:23 PM   #21
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Doing this will not adversely affect your engine performance. It will give you a bad smell at red lights, though. You can make a mil eliminator from parts at radio shack for around 5 bucks to get rid of the light. It is illegal for ON ROAD use. If there is no cel, they usually won't look to see if you have cats. I would say half of the muscle cars on the road today have done away with their cats. I put mine back on because of the smell, and I would suggest a high flow cat over elimination, but thats just me.
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Old 01-22-2011, 06:16 PM   #22
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Originally Posted by Atthehop

Are you in California. Either way the computer knows it there and may spit codes.
Nah in CT, id never do it but I was curious
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Old 01-22-2011, 06:57 PM   #23
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Originally Posted by jeeperharmon View Post
I am about to replace my exhaust manifold ( THree Cracks). IN a 2003 2.4L, and i thought about removing the catalytic converter. is there any difference in driving with one off? any good things about removing. .and i would have it so if i got called to have inspection i could slip the pipe back on.
Pros and Cons of doing this
THanks

WHY REMOVE IT? GUT IT THEN IT LOOKS FINE!!!!!!!!!!
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Old 01-22-2011, 09:36 PM   #24
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WHY REMOVE IT? GUT IT THEN IT LOOKS FINE!!!!!!!!!!
How would u gut it? And would that help with performance?
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Old 01-22-2011, 09:41 PM   #25
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Doing this will not adversely affect your engine performance. It will give you a bad smell at red lights, though. You can make a mil eliminator from parts at radio shack for around 5 bucks to get rid of the light. It is illegal for ON ROAD use. If there is no cel, they usually won't look to see if you have cats. I would say half of the muscle cars on the road today have done away with their cats. I put mine back on because of the smell, and I would suggest a high flow cat over elimination, but thats just me.
Muscle cars died off right about the time catalytic converters were introduced.
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Old 01-22-2011, 09:50 PM   #26
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If you do pull it off recycle it. I have been told there is platinum in them and they give you like $30 for each one of them you recycle or so I heard.
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Old 01-23-2011, 11:05 AM   #27
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How would u gut it? And would that help with performance?
If you take it off then just run a very long rod threw it and just start hammering away until you can see threw it. If the input and output exhaust pipes don't exhactly line up in a straight line then you still can punch it but have to punch it from each side or you can cut it open then reweld it back up. the performance gains isn't all that much but your engine does not get has hot and i saw a better fuel gain and not to mention awesome sound with a good muffler. And you don't ever have to replace it again other than if it rust out but since it doesn't get has hot then it shouldn't wear out as quickly.
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Old 01-23-2011, 12:10 PM   #28
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If you do pull it off recycle it. I have been told there is platinum in them and they give you like $30 for each one of them you recycle or so I heard.
Yeah, they're worth some money for scrap... in fact, in some places, catalytic converter thefts are actually quite common with scrappers.

I would like to second the recommendation of a high flow cat...they're legal, they're not too expensive, they won't cause a CEL, and they'll still make your exhaust sound cooler. I put one on my old truck after my original cat started to break apart...I think I went with a Carsound/Magnaflow high flow cat.
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Old 01-23-2011, 01:00 PM   #29
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Muscle cars died off right about the time catalytic converters were introduced.
you must not follow racing much then, because the muscle car theme is alive and well. and where it is alive and well, those vehicles will flat out smoke the fastest thing ever made pre-1973 (pre-cats)...and they'll do it getting 18mpg or better. Corvette's, Cadillac CTS-V's, WRX STI's, EVO-8's, light modded Talon TSI's, SRT-4 Neon's, Buick Grand National's, chipped diesel trucks that weigh 8000+lbs...will all leave a stock 1970s muscle car in the dust no problem...and get better mileage than the muscle car, even with catalytic converters.
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Old 01-23-2011, 01:23 PM   #30
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Muscle cars died off right about the time catalytic converters were introduced.
What is your definition of a Muscle car? A family car nowadays has more power than muscle cars of yesteryear. Look at the 350hp 6cylinder Taurus, the G8, the SRT8 Charger, the Cadillac CTS-V. Now look at the 400+hp Mustang, Comaro, GTO, and the Challenger. The V6 version of these cars still have more power than most of the Muscle cars of back then. This is not to mention, that there are 6-800 hp street cars all over nowadays. With a pulley change, you can get 500 out of a Terminator. Jeep SRT8, need I say more.

Edit: Oops, should have read to the end. I didn't see Unliminted's post.

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