1996 Honda Civic EX D16Y8
Parts involved: eBay header and megan test pipe.

I feel like this O2 sensor would not be getting a very good reading. Kind of hard to tell in the picture, but it's basically only coming off one cylinder. Should I get an O2 extension and move it to the next O2 sensor, which is further back on the down pipe part?

I've been dealing with some performance issues and with P0420 (Catalyst System Efficiency Below Threshold). It was throwing P0420 but went away awhile ago and recently came back. I used the non fouler trick where you drill one out to 1/2" and screw it in the other and put the O2 sensor in the one with the 1/2" hole. This basically just pulls it away from the replacement cat because it has a higher flow of exhaust.

The code is gone as of now after I fixed it and pulled the negative wire to the battery. I'm pretty sure I have an exhaust leak because the non foulers are long and bump into the chassis now and so I can't tighten the test pipe properly (I think) and I messed up the donut gasket on the test pipe to the down pipe so it's not sealing correctly.

I know if you have bad O2 sensors or readings you can suffer from MPG loss and power loss. Which I am (well, was. IDK how my MPGs are doing considering I just did this last night. And IDK how it's performance is because I haven't had a chance it try it really. I will when I get off work or take a lunch break). I think I do have an exhaust leak because at some certain RPMs the change in my cup holder kind of bounces because of vibrations. But I don't know if I need to replace/move the O2 sensors or not. I'm thinking I should just go back to a stock cat. Or maybe get an O2 extension for the O2 sensor for my cat and put that one on the down pipe and keep the one on the header, on the header..

And when I was looking at my O2 sensor that goes to my test pipe, it was pretty black. Should it just be replaced?

Throw some suggestions my way.. I'm starting to get stressed out about it.
I apologize if this is confusing at all. I'm trying to explain everything I've done and know the best I can without writing something that takes 15 minutes to read.

 

If you have a second location more suited to getting a more "rounded" reading then move it further down. As long as it's pre-cat.

 

No that will be just fine. Many headers have the O2 sensor there and many Hondas have the sensor in a similar spot. You are correct in thinking that having the sensor at the back of the header gets a more even reading of the AF mixture. If you have a wideband use the rear location for that.

 

Thanks guys. If you could answer my other questions embedded in the first post I wrote, that'd be great. Trying to figure out what I should do..

 

I ran a "defouler" and I never had the issue you are having and i am running a test pipe as well. I didn't have to drill anything though. The test pipe has a provision to mount an O2 sensor. Just screwed in the defouler/extension and then screwed the second O2 sensor in. This was before I got turbo'd of course.

 

Not running a cat will cause the PO420 cat code and you will fail emissions. The best way to get he code to go away is to do a OBD1 conversion as the OBD1 ECU's dont look for a cat or a second O2. There are other "tricks" the make the ECU think there is a cat but non are 100%. The second Oz sensor needs to see a different level of air then the first with a preset range, if the sensors read anything out of that preset range it will cause a CEL within a few drive cycles.

 

Hmm.. Well if I didn't drill it out, it wouldn't screw in to the first defouler. IDK, it's really annoying.
When I'm driving I can smell gas. Especially when I step on it. Just means I have an exhaust leak right?

 

Honestly I'd put the primary 02 in the location at the end if the collector. Replace your test pipe with the factory cat and put the secondary back there. The test pipe isnt going to net you that much power if any and IMO makes the car sound raspy.

 

That's kind of what I was thinking about doing. Just wanted some more opinions.
And the test pipe actually gives it a deep sound. My exhaust is not raspy at all. Back in the day (when I bought it) I thought a test pipe was a good HP gain, but I've learned otherwise. So looks like I'll be looking for a stock cat and get an O2 extension for the O2 sensor on my header.


What stock cats will work for my 96 civic ex?

 

i don't like the location, as the angle of it can cause premature failure of the sensor.

 

Yeah, I'll be moving it to the second location which is further back on the down pipe.

 

Test pipes are good for 5-10 whp on a stock motor, seen it time and time again on the dyno. Not worth it if you have emissions laws in your area though.

 

On what?! A K20? H2B? Hahaha.

 

really? show me one dyno where ONLY the cat was removed and a pipe welded in place that gained that much hp.