engine light on after test pipe put on

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Senior Member

I have a friend with a 99 civic si. He FINALLY put an exhaust on it and then I put a test pipe on for him to replace the stock CAT. I hooked the O2 sensor back up just how it was on the stock cat and the car ran great for about two days. Then his engine light came on and the car started running really sluggish. I unhooked the battery for a while (to hopefully reset the computer) and I also checked the sensor to make sure everything was ok.
It looked fine and so I hooked the battery back up and the Engine light was off. We took the car out and it ran great. After about 20 miles, the light was back on and it was running crappy again.

I've heard of other people having the same problem and A different friend that has a 2000 civic si had the same problem as well. He cut his O2 sensor off (which is just plain idiotic).

Anyways, I've asked around a million places, and nobody seems to have an answer for me. In the meantime, my friend has put his stock CAT back on and the car is back to running good.

What is the solution for this problem? There has to be one, or else they wouldn't sell test pipes for these cars.

Please help.......thanks in advance


Super Moderator
crap we had an article about this a little while ago, we must have lost it when the site crashed, i'll keep trying to find it.

One thing that you should do instead of a test pipe is put a hi-flow cat on there, better for the environment. Pills will probally be on here and he'll tell you what to do. i know that there is a way to solve it


Senior Member
dont put the sensor in the test pipe, put a bolt in there that is the same size. this is going to sound like jerry rig because thats what it is but it worked for a friend, zip tie the o 2 sensor to something underneath . you should probably have somthing to adjust air fuel like a apexi vafc to get it right. its running like shit because your computer is compensating for the change, its adding to much fuel or to much air. might work might not just trying to help. or do like asmallsol says and get an after market cat.


Junior Member
I had the same problem when I made a testpipe for my car. I found someone on ebay that made an O2 simulator for the second O2 sensor. It took forever to find one. I couldn't find anything for a civic in summit but they do have some for other cars they might have some for civics now.


GNU/Linux Evangelist
The reaseon your are having problems is an OBD2 car uses 2 O2 sensors. Your ECU is looking for an improvment in emission after the cat.

That being said test pipes are seriously :ghey: as are the people that insist on using them. You won't get but 1-2 hp if your are lucky. If you are simply sure that you *have* to run something like that get a high flo cat.