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Discussion Starter · #1 ·
Got a low system performance code for one of my cats. It's pretty much plugged. Killing my gas mileage. The engine is freshly rebuilt. I don't have emissions testing in MI so I don't care about the cats. Pre cat O2s control my air fuel mixture so I'm good to go. Surely someone makes that down pipe for the 4.0 without the cats right? I found one somewhere last fall and now I can't find it again for anything. Thanks ahead of time for any info. I'm not exactly a great pipe bender. I really want to find a pre fab.
 

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They used to sell bolt on pipes to replace cats called test pipes but I think the EPA cracked down on them

You can typically remove cat and use a big punch and hammer to brake up the catylist brick inside and dump it out I have seen it done on some older cats anyway

Last resort cut the inlet and outlet off your old cat and replace body with a length is straight exhaust connecting inlet and outlet
 

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I believe on some tj's the downstream O2 also plays a role in fuel tuning. Not sure if it's all years though, or just later models.
 

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Discussion Starter · #5 ·
Yea, I thought about just cutting out the cats but the entire exhaust needs to be replaced. I wish I could remember where I saw them before.
 
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