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My friend and I have the same civic LX 1.7 except mine is a manual, his oem manifold rotted at the head flange so he decided to purchase the inexpensive header from ebay, he installs it without the springs to mount the oem exhaust to the header flange which is how they do it, I personally would try to put the springs back in, anyways, he did not get a check engine light which is cool, and the lower oem 02 bung doesnt have any type of shield or anything like that so why no engine light ? the top 02 bung is on one tube rather than in the middle of the oem exhaust manifold, so my question is, can you remove the material from the oem converter to hollow it out and still not have a engine light ? I know their has to be civic owners with the LX 1.7 that has done this.

 
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not legally...

Not sure how your friend removed the cat and has no check engine light, does his check engine light work?

 
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works fine

 
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There must be something in the design of that aftermarket header that doesn't allow for proper exhaust flow over that second sensor

 
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i thought the same thing but its not covered up, you can see the 02

 
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If the second sensor is not in the exhaust flow it may not trip the CEL. The first sensor is for A/F ratio I believe.

Either way you should get a cat added wither an Ex one or aftermarket.

 
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go on ebay you can see them, they are around 45 dollars with shipping, the only difference with the photos is they moved the top 02 to the left side and the bottom 02 is still on the right. just look up lx header 2001-2005 they only have one style that everyone sells.

 
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Oh I have seen them. They have been selling them on eBay for a long time!!

Does he have an exhaust leak that would cause the exhaust to not reach the sensor?

Hey if it worked for him give it a go!

 
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I recently had a '03 LX which had an aftermarket header when I bought it. It had an o2 sensor code at first but after clearing it didn't come back until like a month later.

 
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no leak, he just put the new header on and its very quiet. he put the header on because of the oem manifold was leaking where a tube was rusting out near the head mounting flange, it has the oem full exhaust and its not even louder than that stock manifold with the cat converter, so that tells me that oem manifold with converter must not have much restriction if the sound out the exhaust doesnt change much

 
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I think you're confused.

is it possible he has a 1.7 ex modle?

the upstream sensor on both lx and ex and is the Air/Fuel ratio sensor. The lower sensor in the cat is the O2 sensor, which has different positions depending on lx or ex.

if his is an ex then the only connected sensor to the header is the AF, which does not read the cat O2 signal.

 
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im not confused i know what a lx and ex model is. and since i bought my car new in 2001 i definitely know that i have a lx with a convertor on the manifold and his 2003 is identical to mine except for the automatic transmission, his car is doing great with this header on it. we got the header for a LX not a ex that is why the 02 bungs are where they are, you can buy a header for the EX which is slightly different, they make this to have the oem exhaust pipe bolt up to it.

 
Rep Power: 229

Oh, cool, good to know.