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Unread 02-16-2014, 09:13 AM   #1
antcg
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98 Cherokee needs a Cat

So I've had my jeep a month now and not to long ago I realized that someone removed the cat and welded a straight pipe from the muffler to the front pipe and completely removed the downstream o2 sensor which is probably why my CEL is on.

I live in Alabama so we don't have inspections. I want to get better gas mileage and get my cel off so I know I need a new o2 sensor, but would it be more reasonable to just tap the straight pipe and throw an o2 sensor in or buy a new cat and try to saw off the old pipe from the front pipe and muffler and put a new o2 sensor assuming I can save the muffler and front pipe.

Which one would get me the best results as far as gas mileage? And I do like the sound it has without the cat on, but whats the best option for gas mileage and price?

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Unread 02-16-2014, 09:26 AM   #2
Timo_90xj
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Only upstream O2- sensor controls air-fuel mixture. Downstream O2- sensor is there to sniff if the cat converter works or not, and to throw on the CEL if it doesn't. As far as I know, having a cat converter is a federal requirement in the USA so you better have it under there no matter if you have inspections or not.
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Unread 02-16-2014, 09:40 AM   #3
mschi772
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And because people breathe air, we'd all appreciate it if you would reinstall a cat so that the air we're breathing can be cleaner. A cat will not hurt your gas mileage.
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Unread 02-16-2014, 09:46 AM   #4
antcg
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Quote:
Originally Posted by mschi772 View Post
And because people breathe air, we'd all appreciate it if you would reinstall a cat so that the air we're breathing can be cleaner. A cat will not hurt your gas mileage.
I enjoy breathing clean air too. I wasn't saying it would I was wanting to know if having an o2 sensor and no cat or o2 sensor and cat would give me better gas mileage. I just currently have little money and was wanting a cheap solution like just tapping the pipe.

Could i get away with a cat from a scrapped cherokee and throw a new o2 sensor on there?
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Unread 02-16-2014, 10:23 AM   #5
L_Kilkenny
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I'm in the same boat as you, 1998 and PO removed the cat. They did an even a crappier job and used flex on mine so I keep debating what to do. Timo is right, only the front O2 sensor controls the mixture BUT the back O2 sensor will send the system into limp mode which does effect performance/mileage. ASfar as IF you should do something that is a completely personal choice. I have no problems driving a vehicle designed without a cat so there is no compelling reason outside performance/mileage for me to put one back on. A vehicle without a cat is a vehicle without a cat regardless of year. A person that wouldn't put a cat on vehicle made before the mandate (1875 model year) doesn't have much of a environmental stance telling someone they should put one back on a 1998. Would you drive a vehicle made before the mandate? Would you put a cat on it?

As for what to do........ I keep bouncing around a few ideas. Perhaps the easiest is to buy a cat and sensor and re-install them. Aftermarket high-flow cats are around $100, sensor $40-$50(?). Add misc hardware.
Third is leave it as is. Good luck with your problem.
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Last edited by chris87xj; 02-16-2014 at 11:57 AM.. Reason: option 2 removed
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Unread 02-16-2014, 10:40 AM   #6
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I think that conforming to federal emissions regulations is not only vital to your jeep running correctly but to the survival of your thread on this forum.
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Unread 02-16-2014, 11:29 AM   #7
M35A2
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If you can buy the cat at a salvage yard, i'd do that, O2 sensor too. Out here in Ca. you can't buy a cat from a salvage yard, gotta go to the muffler shop.
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Unread 02-16-2014, 11:41 AM   #8
chris87xj
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Subscribed. I have no issue with a thread about how best to put a cat back on your xj.
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Unread 02-16-2014, 12:23 PM   #9
antcg
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I mean I most definitely want to conform to federal law, although I've never heard of anyone getting caught for this, I know I sure don't want to be the first. Out of curiosity does anyone know what kind of offense driving without a cat is and what the consequences are? I personally want my jeep to last as long as possible and be as stock as possible with a few mechanical upgrades here and there and I guess the POs didn't?

I might try to get a cat and o2 sensor from a junkyard to save a couple bucks and see the results before I go spending money on a high flow cat and new o2 sensors. And as I go to put it back on the cat connects to the front pipe with a gasket and bolts correct? I'm worried the PO may have welded to where I can't use that pipe anymore.
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Unread 02-16-2014, 01:20 PM   #10
chris87xj
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Quote:
Originally Posted by antcg View Post
Out of curiosity does anyone know what kind of offense driving without a cat is and what the consequences are?
It's a moral offense towards everything else that lives on this planet, and if it's wrong isn't that consequence enough?
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Unread 02-16-2014, 01:38 PM   #11
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Quote:
Originally Posted by chris87xj View Post
It's a moral offense towards everything else that lives on this planet, and if it's wrong isn't that consequence enough?
Ha! I believe that getting your jeep running right is more than enough incentive in this case.
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Unread 02-16-2014, 01:53 PM   #12
antcg
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Quote:
Originally Posted by chris87xj View Post
It's a moral offense towards everything else that lives on this planet, and if it's wrong isn't that consequence enough?
HAHA When you put it that way..

Point taken, find new cat and o2 sensor ASAP!
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Unread 02-16-2014, 03:09 PM   #13
M35A2
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You might be better off going to a shop that sells the stuff though. You'll still need to have it installed, unless you can do it yourself, then, if you got a cat that was failed, you just wasted dollars on it. Maybe new is the better way to go?

Check this out....
http://www.ehow.com/list_6946274_ala...onverters.html
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Unread 02-16-2014, 04:00 PM   #14
mschi772
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Well, as was said by Timo, your MPG will only be affected by the pre-cat O2 sensor which should perform its function with or without a cat. Cat's aren't terribly expensive especially if you shop around a bit (I've seen guys link some affordable sources with quality cats around here but don't remember them), and aren't any more difficult to install than any other piece of exhaust pipe/muffler. In order to clear your CEL, you'll need both O2 sensors and a cat. If it would interest you, installing a piece of flex after the header and/or between the cat and muffler can ease some of the stress on the exhaust system especially if it hits an rock or other object while wheeling.
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Unread 02-16-2014, 04:16 PM   #15
antcg
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Quote:
Originally Posted by M35A2 View Post
You might be better off going to a shop that sells the stuff though. You'll still need to have it installed, unless you can do it yourself, then, if you got a cat that was failed, you just wasted dollars on it. Maybe new is the better way to go?

Check this out....
http://www.ehow.com/list_6946274_ala...onverters.html
Well I'm pretty sure I can do it myself. I do most of the work on it myself now. If I can find a cat at a junkyard for a cheap, cheap price I'll go for it.

Eventually I want to get a high flow cat and a cat back exhaust system, but for now I just need something to get away with I suppose, until I can afford new or else drive it the way it is now until I can afford new.
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catalytic converter , front pipe , muffler , o2 sensor

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