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  • Do TJ's Need Catalytic Converters?

    I have a 97 Wrangler, 4.0L and my downstream O2 sensor is going out.

    I was thinking of just getting rid of the Catalytic Converter all together when I take it in to et my flowmaster put on and not bother with the replacement of the O2 sensor.

    Can I do this? Or will my jeep just not run good after doing this?


    Thanks

  • #2
    Short answer, yes, it needs the converter, both for emissions and computer control.

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    • #3
      Cat

      Yes you do. You will hear that if you remove it you will gain hp...blah blah blah. Blup is right the computer is programed to run with one. So removing it actually will end up hurting performance. If you are concerned get a high flow and install it when you are replacing the O2 sensor.

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      • #4
        Yep, keep the cat. Stock one flows pretty well for our motors, but you can always go aftermarket. Cats have come a long way and they don't restrict much, and unless you're gonna carb your motor and pull the fi, it needs the cat to run correctly.

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        • #5
          my brother and neighbor are big into using their laptops to adjust computers in cars, i asked about this when i first got my jeep, i wanted to run the open borla header cause i like loud cars, they said they could program it to say there is one there but it will always say the motor is at normal operating temperature, but the check engine light wont be on so it will pass emissions, i'll probably try this when the sensor goes bad or i need a new cat, but right now im leaving it the way it is, got to many other projects

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          • #6
            Simple answer yes, ...

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            • #7
              I would never remove a good one...but mine was shot and I wanted to spend the money elsewhere. Didnt notice any losses or gains with not having one. I just have better things to spend my money on

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              • #8
                Yes!!!

                Not sure the laws in other states but here in NY you don't pass inspection if your check engine light is on with vehicles newer than '94... your OBDII gets hooked up and all the codes are read so you can't just bypass the light... from my understanding this is supposed to be the trend across the country to go to similar standards... and for the minimal gains if any in performance why add all that pollution to the air??

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                • #9
                  Here for the mandatory emissions check they put your vehicle on a dyno and stick a sensor in the exhaust pipe. A computer will read out EVERYTHING. They also do a visual inspection as it is a CRIME to remove the catalytic converter. As was said, since the engines now are designed to work with the cat, you may very well lose power, by removing it and you will definately create more air pollution.

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                  • #10
                    My cat was chopped off when i got it.....the second 02 sensor is right infront of the muffler....never get any codes....

                    OH...i do have the stage II chip though....
                    Last edited by Jodean; 08-14-2007, 08:55 PM.

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                    • #11
                      You won't always get codes with no cat, but I can almost guarantee that on an OBD2 vehicle, you aren't getting as good of fuel economy without one.

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                      • #12
                        On an ODBII vehicle (your Jeep) the computer uses the O2 senesor to adjust fuel and spark timing. Theres a little principle for burning chemical reactions called stoichiometry that your computer uses the O2 sensor to regulate. Ideally the air/fuel ratio for gas to burn efficiently is 14:1. The O2 sensor monitors oxgen content in your exhaust to adjust spark timing and fuel to try to keep it as close to 14:1 as possible and there are conditions in your fuel maps that will allow it to get as low as 12:1, but again this is controlled by the other sensors on the Jeep, like intake temp, water temp ect. You cant just take away this sensor and hope your computer will overlook it. Your computer will go into the "warmup" mode called open loop where the computer ignores several sensors, including O2 until certain conditions are met. This mode essentially runs the vehicle lean with advanced timing so that it will warmup quicker.
                        If you only have 1 O2 sensor before the cat, removing the cat has 0 effect on vehicle operation. Newer vehicles have 2, one before and one after. If these are not in agreement they will throw the computer into "limp" mode and you'll have to explain to the dealer why you pulled the cat so he doesnt call the feds on you for disabling a federaly mandated emision control device.

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                        • #13
                          My 03 TJ only has 1 o2 sensor in the exhaust system, and it is before the CAT. I cut mine out a while ago...no emissions in Ohio (at least not my county)

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                          • #14
                            I have a 97 TJ with a 4.0, I have been running with out a cat for about 5 years now. I went threw 4 of them during the warrenty period. After the cat was not covered any more and needed replaced for the 5th time I just cleaned it out. Never had a problem with the O2 sensors. or the OBII. And here in Pa. we do have emissions testing and I have pass every time.

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                            • #15
                              <<<<<<<<<<<<treehugger here>>>>>>>>>>>>>>>>>>>

                              Please refrain from removing the cat, the small gains you may or may not get, or the decrease in reliability/performance are not worth it. Now LumberJack, you are an exception, I don't blame you since you've had all those troubles, and if you pass emissions, guess you're good.

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