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I have a 2001 Civic HX. I’m currently having o2 sensor issues and the first cat is clogged up. I’ve wanted to put a header on the car anyway, so I was wondering if I could successfully(meaning without fault codes and while keeping stock ecu and exhaust) delete my first cat that’s at the stick manifold; but keep the second cat that’s up underneath the car and the rest of my exhaust with it. Please let me know. If I can install a header while also solving my o2 and Cat issues, that would be fantastic. It’s the D17A6 on an HX(lean-burn VTEC) just for clarification.

 
Rep Power: 221

The computer might not be happy with it missing a cat. You'd probably get a p0420

 
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yeah, I assumed as much. So, there isn’t any way for me to fill the ecu or something along those lines?? I know plenty of people do cat deletes so I’m sure there has to be SOME way for me to get around it. Since it has two cats and usually people delete their only cat(s), I assumed I could deal with it some way. Let me know if you have any ideas please. I’m well aware of computers causing serious issues, Ive been dealing with my car being annoying for months now all because of one o2 sensor code putting the car in limp mode and all so I want to get this stuff fixed and over with. I’d also like a header and the one cat delete too tho lmao. If I get a header, I literally HAVE to delete one of my cats. I guess I could technically keep both of them but I’d have to cut the stock manifold up since the first cat is directly below the stock header where the pipes all converge into one so it would make the most sense to get rid of that one with the stock manifold. My thoughts were that I’d just move the o2 sensors so that they were in the same general spots as stock, just on the modded exhaust. I’d put the A/F o2 above the first(second in stock form) cat, then the other one below it and then that 3rd o2 sensor is supposed to be in front of the second cat but I’d just put it in the pipe and there won’t be a cat, or I could use one of the fake or whatever you want to call it o2’s for the third one

 
Rep Power: 221

On a normal car you can use a defouler on the secondary o2. However I'm not sure on this car because of all the extra crap