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Old 01-29-2013, 08:43 AM   #1
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No Catalytic Converter

Hello everyone, this is my first post on this site, hope its worthy of discussion. I just bought my first jeep about a month ago. Its a 1999 tj 4.0 sport. The po was the original owner, it has 132k miles on it, superlift 4" suspension lift, 35" buckshot maxxis tires, hardtop, good looking rig. Anyway, he had replaced the faulty header with a better one supposedly and put a flowmaster muffler under it (kinda raspy sounding) but cut the catalytic converter out. He said he did it for performance, but I think he did it because cats are expensive and he didn't want to pony up the dough for a new one. So I have the wires for the rear O2 sensor taped up and tied off. I have put about 1000 miles on it since I have gotten it (who knows how many he put on it like this) and it seems to run just fine. There is no gassy smell, no sooty exhaust, I'm not overly concerned. The only thing that bothers me is that rear O2 sensor not being in there, I know the computer gets a reading and adjusts the fuel mixture based on the difference between the first sensor and the second one, but what is that missing sensor telling the computer? Guess I could pull a plug and see if its rich or lean? I am considering welding in a bung and replacing the sensor. Im not overly concerned with the missing cat, I don't drive it on the road THAT much, just buzzing around the farm (literally, the thing sounds like a bee with that flowmaster and no cat). Thoughts, experience with this?

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Old 01-29-2013, 09:19 AM   #2
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I had mine cut out as well. He ran my pipe through my cat(hollowed out) so I don't think he ever messed with my O2 sensors. I'd say as long as you MPGs aren't too bad you're fine..

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Old 01-29-2013, 09:26 AM   #3
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In earlier TJs like your '99, the 02 sensor on the cat just tells the computer whether the cat is working or not and it has no effect on the fuel mixture. It wasn't until 2001 or so when the 02 sensor on the cat started having a small role in setting of the fuel mixture.
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Old 01-29-2013, 09:29 AM   #4
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Good to know^
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Old 01-29-2013, 09:30 AM   #5
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Originally Posted by reissigree View Post
I had mine cut out as well. He ran my pipe through my cat(hollowed out) so I don't think he ever messed with my O2 sensors. I'd say as long as you MPGs aren't too bad you're fine..
Not too sure about the MPG's would be hard to determine that since I'm not on the road much with it, but I have been doing some reading and MOST of the time a "faulty" O2 sensor will make the fuel mixture a little rich (safety feature) but with the better header and free flowing exhaust it might actually be a proper adjustment. I dont know, If i get bored I will weld one in there. Probably get a whole new exhaust eventually anyway, don't know how long I can take that bumble bee sound.

A side note, I heard a thumping under the jeep when I got it, that flowmaster muffler was banging against the drive shaft yoke when i would hit a bump, the exhaust is a hack job like frankenstein. I bent the hanger out a little bit to clearance it, so far so good.
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Old 01-29-2013, 09:38 AM   #6
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Quote:
Originally Posted by Jerry Bransford View Post
In earlier TJs like your '99, the 02 sensor on the cat just tells the computer whether the cat is working or not and it has no effect on the fuel mixture. It wasn't until 2001 or so when the 02 sensor on the cat started having a small role in setting of the fuel mixture.
Thanks, very good to know indeed! So I guess I will just keep the check engine light bulb out of the cluster, lol.

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