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Thread: Catalytic Converter Help

  1. #1
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    Default Catalytic Converter Help

    97 TJ/4.0L

    I have a replacement CAT for my Jeep I bought from AutoZone. Problem or issue/non-issue is, the replacement is much smaller than the stock CAT. Inlets and outlets are the same but the body of the CAT itself is smaller. For example: if the stock CAT were hollow, I'd be able to fit the new CAT inside of it.

    My questions: Would the size difference cause the computer to start dumping codes at me? Should I try and find the same size replacement CAT? Autozone says it would work, should I trust their counter guys word on that?


    Thanks
    RP
    97 TJ, RE 5.5, 17" ATX Wheels, 37" BFG/KM2's, D44's f/r widened width, 5.13's, ARB rear, PowerTrax No Slip front, Tera 4:1/2Lo, Full Armor, 1ton Steering, Warn 9.5ti, Currie F/R bumpers, York OBA, PSC Full Cage, bunch of other chit!

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  2. #2

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    The outlet inlet holes are the things you need to worry about. Autozone as well as everyone else sells a universal Cat which they use for all makes and models. I am sure you paid alot for the one at Autozone too..

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    Because I live in California I'm restricted to the replacement model I choose. It has to be California compliant. I was more worried about the smaller CAT body size than anything. Price was comparable to most places.
    97 TJ, RE 5.5, 17" ATX Wheels, 37" BFG/KM2's, D44's f/r widened width, 5.13's, ARB rear, PowerTrax No Slip front, Tera 4:1/2Lo, Full Armor, 1ton Steering, Warn 9.5ti, Currie F/R bumpers, York OBA, PSC Full Cage, bunch of other chit!

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    Default

    You should be fine. Just have a muffler shop weld on some extensions.

    The universal cats they sell are small so that they fit into tiny cars.

  5. #5
    Monkey Wrench! JWebber's Avatar
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    You will be fine. The only thing that 97 up to (2000 models I think), The down stream sensor, all it's does is just monitors back pressure thats it, in other words. If the sensor does not get the right amount of exhuast flow it kicks a code, but the codes it kicks if telling the other upstream sensor to calm down. Fuel and air ratio 14:1 will be high or low,that will be why you will get a code. You will be good to go! :burnzout:

  6. #6
    www.stu-offroad.com Stu Olson's Avatar
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    Quote Originally Posted by JWebber
    The down stream sensor, all it's does is just monitors back pressure thats it, in other words. If the sensor does not get the right amount of exhuast flow it kicks a code, but the codes it kicks if telling the other upstream sensor to calm down.
    Are you certain about that?

    I could have sworn that the down stream O2 sensor's reading is compared to the upstream O2 sensor's reading to ensure that the catalytic converter is in fact working....in other words, the exhaust gases coming out are cleaner than those going in. Once the difference between those two sensor readings become small enough, the check engine light is turned on and a code is thrown to indicate the cat is no longer doing its job. The upstream sensor is monitored by the PCM to ensure the proper air fuel ratio is being achieved....if it is not, the injectors are adjusted to richen or lean the mixture.
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    Good information to know.

    After researching the FSM and asking more questions, I was able to determine that the critical part of installing a new CAT is to make sure upstream and downstream O2 sensor separation is maintained at the factory distance.

    After everything was mocked up, I ended up extending the exhaust pipe in front of the new CAT to maintain the downstream O2 sensor position. After replacing O2 sensors front and rear of the CAT I'm now good as new!

    A good weekend maintenance project and I learned a bit more about the exhaust system as well.

    Thanx-o-bunch
    97 TJ, RE 5.5, 17" ATX Wheels, 37" BFG/KM2's, D44's f/r widened width, 5.13's, ARB rear, PowerTrax No Slip front, Tera 4:1/2Lo, Full Armor, 1ton Steering, Warn 9.5ti, Currie F/R bumpers, York OBA, PSC Full Cage, bunch of other chit!

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    Pog Mo Thoin LoneJeeper's Avatar
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    there's also an emissions warranty on some jeeps... i'm not sure what it is, but you might get a break there.

    lj

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    Registered IBTJn's Avatar
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    Well for what it's worth, I've had to replace 2 cats on 4.0 Ltr. engines. My old '88 MJ (sold it a few years ago), and my wifes '95 XJ (my TJ's is still good). The muffler shop that installed the one on my MJ told me the smaller one was fine, too. 4 months later it wouldn't pass emmisions...which California emmisions are even more strict than ours. I ended up having it replaced yet one more time. It went through without a problem. On the wife's XJ, I didn't make the same mistake twice. I went right to the HD unit (larger universal). The shop that installed it knew all about this problem with the smaller cats. It also passed with flying colors with the larger cat.

    So, if you have to take your rig through emmisions (as we do), then I'd say get the bigger cat. If not, then it's probably not going to be an issue. My MJ ran fine on the smaller cat, just wouldn't pass emmisions.

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    Quote Originally Posted by IBTJn
    Well for what it's worth, I've had to replace 2 cats on 4.0 Ltr. engines. My old '88 MJ (sold it a few years ago), and my wifes '95 XJ (my TJ's is still good). The muffler shop that installed the one on my MJ told me the smaller one was fine, too. 4 months later it wouldn't pass emmisions...which California emmisions are even more strict than ours. I ended up having it replaced yet one more time. It went through without a problem. On the wife's XJ, I didn't make the same mistake twice. I went right to the HD unit (larger universal). The shop that installed it knew all about this problem with the smaller cats. It also passed with flying colors with the larger cat.

    So, if you have to take your rig through emmisions (as we do), then I'd say get the bigger cat. If not, then it's probably not going to be an issue. My MJ ran fine on the smaller cat, just wouldn't pass emmisions.

    Story of my life, 'day late/dollar short'. I wish I'd know about your smog testing problems before I installed the smaller CAT. Oh! well, I just passed smog in April so I'll have two years until I have to try and pass again. The new O2 sensors may help pass smog. The original 02's were 8 years old , the 8 year old CAT just finally gave up the ghost and had to get replaced.
    97 TJ, RE 5.5, 17" ATX Wheels, 37" BFG/KM2's, D44's f/r widened width, 5.13's, ARB rear, PowerTrax No Slip front, Tera 4:1/2Lo, Full Armor, 1ton Steering, Warn 9.5ti, Currie F/R bumpers, York OBA, PSC Full Cage, bunch of other chit!

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  11. #11

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    Quote Originally Posted by 4cornerzJeeper
    Autozone says it would work, should I trust their counter guys word on that?
    RP

    UNDER NO CIRCUMSTANCES...even if you asked them whether the screwdriver in your hand was a phillips or not...go ahead and check that with someone else. GOOO AUTOZONE.
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    I dont think the size of cat matters on a jeep. If you had a big v8, maybe but not on our jeeps especially if its a 4 cylinder. I just put a really small $40 cat from summit on my Jeep and it passed smog with no problem. It isnt even a california cat, I just welded the o2 sensor bung into the cat and that basically made it work the same. I had an exhaust guy show me the difference and he said the later year cats only add an o2 sensor and triple+ the price.
    97 TJ RE3.5, 33X12.5, Flowmaster exhaust, Free flow cat, TC intake, 4.88's, Custom Stereo w/ 2 10's, MP3 Computer w/ 10gigs of music

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    I don't mean to hi-jack your thread, but how do you know when your cat. converter is bad? I've got some nasty exhaust sounds and a real hot metal smell after my jeep warms up. Does this sound like a cat? Any help would be appreciated.
    "Do nothing out of selfish ambition or vain conceit, but in humility consider others better than yourself"

    98 TJ, Fabtech Longarm Lift, Fabtech Front Bumper, Warn Diff Covers, 6" P.I.A.A Lights, Xenon Extended-Flares, 4.88 Gears, 35" BF Goodrich MT, FlowMaster Exhaust, AA SYE, super 35 upgrade...4 banger...

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    I have actually never had a cat go bad. Both of mine broke up and rattled like crazy. They still work like this but can break up further and reduce flow, plus the rattle is annoying. I have heard that if it actually goes bad it smells like rotten eggs. But I have never experianced that before.
    97 TJ RE3.5, 33X12.5, Flowmaster exhaust, Free flow cat, TC intake, 4.88's, Custom Stereo w/ 2 10's, MP3 Computer w/ 10gigs of music

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    Default Rotten Eggs

    Hi,

    The cat went out on my old GMC, and it did smell like rotten eggs. Smells really bad.
    Specs (just so you don't have to ask): 2005 Wrangler SE 2.4l with... 2"BB, Teraflex discos, 31x10.50 R15 Bridgestone Dueler AT Revos, Rancho RS5000 shocks

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    As stated above. Smells like rotten eggs. Couldn't stand the smell anymore on my rig and had to do the new install. On the trail it was making everyone sick and in town I'd see people sniffing inside of their own vechicles at the stop lights thinking something was wrong with their vehicle ....good for some giggles but hard on the nose.
    97 TJ, RE 5.5, 17" ATX Wheels, 37" BFG/KM2's, D44's f/r widened width, 5.13's, ARB rear, PowerTrax No Slip front, Tera 4:1/2Lo, Full Armor, 1ton Steering, Warn 9.5ti, Currie F/R bumpers, York OBA, PSC Full Cage, bunch of other chit!

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  17. #17
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    does the rattle go away when the vehicle warms up? I've got this rattle sound that my 98 Wrangler makes when i start up and pull off..but as it warms up you don't hear it. When i stop and park for maybe 10 minutes and it cools down again i'll hear it again. Exhaust sounds fine after it warms up so i don't think it's my flowmaster. I know in most states you can't past smog tests without it, but michigan is pretty lenient. I've heard that you gain quite a bit of power without the cat. Is this true?
    "Do nothing out of selfish ambition or vain conceit, but in humility consider others better than yourself"

    98 TJ, Fabtech Longarm Lift, Fabtech Front Bumper, Warn Diff Covers, 6" P.I.A.A Lights, Xenon Extended-Flares, 4.88 Gears, 35" BF Goodrich MT, FlowMaster Exhaust, AA SYE, super 35 upgrade...4 banger...

    96 ZJ, Laredo, stock with rock rash and rotted radiator.

    05 Ram Hemi 1500 - Completely stock, Tow rig

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