4.0 exhaust downpipe 'cans' - JeepForum.com

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post #1 of 5 Old 12-30-2011, 05:02 PM Thread Starter
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4.0 exhaust downpipe 'cans'

I'm trying to finish up an engine swap ('00 TJ 4.0) into my CJ, and exhaust is up next. My motor has the manifolds, going down to twin openings. I've seen the stock TJ setup, and the downpipe has two 'cans' on it. What are these? Cats?

In a nutshell, I need to determine whether or not I need the stock downpipe with the 'cans'.

Thanks in advance for the help!!

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post #2 of 5 Old 12-30-2011, 05:20 PM
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The cans are indeed small catalysts called "pre-cats"....

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post #3 of 5 Old 12-30-2011, 05:52 PM Thread Starter
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Originally Posted by TJJP77 View Post
The cans are indeed small catalysts called "pre-cats"....
Do you know if they're needed? Needed, as in regardless of emissions. I just need it to run properly.

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post #4 of 5 Old 12-30-2011, 06:23 PM
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They're not necessary for proper engine operation, but you won't find a down pipe that will bolt to the manifolds without the pre-cats.

Are you trying to make the TJ computer run in a CJ, or just swapping the motor over? The TJ is OBD-II, which makes a difference. While it will run without the catalytic converter, the computer will throw a code if it "sees" a non-functioning(or missing) catalytic converter. It has "upstream" and "downstream" O-2 sensors, they up-stream sensors to check A/F ration by exhaust gas analysis, and the down-stream set to confirm the catalytic converter is functioning properly. Remove the upstream sensors, the engine runs open-loop(crappy) remove the cat or downstream sensors, and you get a check engine light.

In addition, the OBD-II system has a gas tank evap. system monitor(Ever have a check engine light because the gas cap was left off?) without all that crap, you get another code and a check engine light also.

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post #5 of 5 Old 12-30-2011, 09:39 PM
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You CAN get the down pipe without the cats for the 2000 exhaust. Napa and Rockauto has them. It's made by Walker.


However, as stated above, it will most likely throw a code unless you've done some modifications to the wiring and computer.

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4.0 swap , cj , downpipe , exhaust , tj

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