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Discussion Starter #1
My exhaust has rusted through and fell to the ground for the 2nd time in a few months in 2 different spots, and upon research I found that many 96-00 exhaust manifolds crack:bs:, therefore I am buying an aftermarket header and exhaust system for my 2000 civic HX to fix my current and any future common problems with exhaust.

In the dx/cx/lx/hx models, the exhaust manifold has the catalytic converter built right into it, before the downpipe. there are 2 o2 sensors, one in the exhaust manifold before the cat, and one at the end of the cat.

With the aftermarket header, it is basically upgrading it into an ex/si header with no catalytic converter built in. In those models the cat is after the downpipe under the center console area, and then goes to the mid pipe, s pipe, and muffler. My new exhaust comes with a test pipe in place of a real catalytic converter. I do not need or want a cat, my state does not test for them. But I know I need to buy an o2 sensor wiring extension for the 2nd o2 sensor to reach all the way down to the test pipe bung under the car.

My question is, if I do that and simply plug in my o2 into the test pipe (high flow cat) bung, won't it will throw a check engine light code for having no catalytic converter because the temperatures will read the same and possibly run badly or in "limp mode?" How do I get around this exactly? I have seen there are o2 defoulers for $30 that are 90 degree right angle design, screw into the test pipe bung, and then o2 sensor screws into that. Will that fix the CEL code? Any suggestions? What is the best way to go here? I dont need a cat and dont want to pay for one either:jerkit:.
Sorry for the essay, but I figured its better to explain exactly what i know and what i need to know.
I need a solution ASAP so I can order my shit and get them on my car because I am borrowing a vehicle in the meantime and need to return it as soon as my car is fixed.
 

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93 Civic del Sol Si
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With an aftermarket header and exhaust you will basically turn your exhaust system into an EX/Si exhaust.

Yes if you were to install the O2 sensor after a test pipe you will get a CEL for inefficient catalyst.

Why the hell would you not run a cat on a street driven car? You're not going to gain any power from removing it, your car will sound like shit if you install a test pipe, and you're going to be releasing a much higher level of pollution into the air. There are cheaper options on the market for a new cat, or find a used one from an EX/Si Civic or other Honda with similar cat. Just use one, plain and simple...
 

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Discussion Starter #3
Yes i plan on searching for a used EX cat, I already did and there are none around here right now. So since I need a fix now and can worry about emissions later, I am using just the test pipe/resonator for a temporary solve.
1... do you all know how long of an extension I need for the secondary o2 sensor? It looks like I wouldnt need too long, from looking down into my engine bay and seeing where the wiring and length of it is for the 2nd o2. I dont want to buy too short, but if I get a 36" wiring and then have a foot leftover, where am I supposed to trail it? should I just make a loop somewhere? lol. sorry, n00b here
 

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93 Civic del Sol Si
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I de-loomed my engine harness a bit to make the secondary o2 harness reach as far behind the motor as I could. And then I bought the secondary o2 for a y8 and it worked perfect for me.
 

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Discussion Starter #6
I de-loomed my engine harness a bit to make the secondary o2 harness reach as far behind the motor as I could. And then I bought the secondary o2 for a y8 and it worked perfect for me.
AWESOME! So you didn't have to buy an o2 extension? I am not sure if I will need to, it kind of looks like it will have enough to reach the downpipe bung, but if there isn't enough room/clearance there to put the o2 sensor, even with my right angle adjustable defouler, then I would have to get the extension and put it in the test pipe bung and would most likely need an extension. Would this work?
Rywire 4-wire 02 Extension Harness - JDM Honda Parts USA - JHPUSA
Because on the site it says it works with 92-95 honda civic all models, but mine is a 2000 HX. but i went outside and looked at my o2 sensor harnesses, and the primary sensor harness is a 5 wire, but the secondary sensor harness IS a 4 wire... weird. This extension on the site is for a Rywire 4-wire extension harness and it looks like it would work, yet the site says only 92-95?? Sorry if this is a n00b question... would this extension work if I need it, or is the site correct that it won't work on my 2000?
 

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Discussion Starter #7
So i just went out to my car again and check the secondary o2 sensor wiring, and it is the standard green, white, black, black 4-wire design, so I am buying this Rywire extension just because I think I might need it, and dont want to NOT have it when i do everything.
soooo if this Rywire 4-wire extension that says for 92-95 DOESNT work for my 2000, then I'll be a monkey's uncle.
 
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