It was mentioned in another thread that replacing your downpipe with an aftermarket unit will result in a DTC from the rear O2 sensor. From what I understand there are 2 methods of eliminating this problem:

1. Install an O2 sensor emulator/simulator
2. Install an anti-fouler between the O2 sensor and downpipe

Since the anti-fouler is the least expensive this is the solution I would like to go with. The first thing I noticed was the width and depth of the anti-fouler was not sufficient to accept the O2 sensor, so I drilled out the center of it.

(Before & After pics below)

The sensor will now thread into the anti-fouler, but a question did arise. Do I want to leave the end of the anti-fouler intact so that the only area of the O2 sensor exposed to the exhaust stream is through the small hole in the end, or do I want to drill completely through the end and expose more of the O2 sensor? I'm hoping to do the downpipe/resonator replacement this weekend so I want to get everything in order now to make the job as smooth as possible - and not have to wind up messing with the O2 sensor in the future. Any insight will be greatly appreciated.

 

There is a third option.... PCM tuning to delete the code.

As for the answer to your question, I am not sure. I'm guessing it won't matter either way. You can leave it as is, drive it and if a code from the rear O2 pops up, disassemble it and drill through the rest of the way.
I have also read where it may take doubling the anti-foulers to accomplish the goal.

The main point is simply to space the O2 from the exhaust stream so it's only reading a limited amount of gases.

 

That's true...deleting the code from the pcm is an option, but not one I really want to entertain at this time. I'm thinking a pcm tune is the last thing on the to do list - after all other mods are in place. That way I only have to pay for the pcm tuning once. I guess I had a Popeil state of mind (set it and forget it) when it came to the O2 sensor. Since the idea is to limit the amount of exhaust the sensor is exposed to I guess I'll just leave the end of the anti-fouler as it is and see what happens. Test fitting the anti-fouler into the downpipe the end of it is approx. 1/4" inside the bung it threads into so it isn't in the direct flow of the exhaust. I was just hoping there was a definitive answer so I could eliminate having to crawl under the vehicle a second time, but if I must then so be it.

 

I put in a ZZP downpipe and SLP Exhaust the rest of the way, she has not thrown a code yet

 

You are going down a road I explored. When I originally put a ZZP 2.5" DP with High Flow cat on my Monte, I thought it would be a LONG time before a tune would be required for my car.
As a result, before I installed the DP, I knew the P0420 code was a possibility and I explored possible options. My conclusion was since getting that code was not a "guarantee", I'll install the DP. If the code pops up, plan B, the Anti-Fouler trick. I drove the car rest of that summer, parked it and whoops, got mod crazy and by the time I took it out for the spring, I had to get my PCM tuned and just had that code deleted at that time.

So, I completely understand your goal. One thing I found AFTER installing the ZZP DP, if I needed to use the Anti-Fouler trick, I was probably going to need some type of 90 degree fitting (did not look like a lot of room between the O2 and car body existed).

 

I didn't get a ZZP downpipe. I am having symptoms of a cat clogging up (verified with vacuum and pressure tests) so started doing some searching around. I came across a NIB Magnaflow downpipe on eBay with only a couple minutes left on it so I threw a bid at it. I won the auction and it was delivered to my door for $100 - about $85 less than the next best price I found on them. Replacing the downpipe made more sense to me because that way I can get rid of the U bend at the same time. I haven't made a physical measurement under the car yet to see if there will be a clearance problem with the anti-fouler, but since it exits the downpipe from the side instead of the top I'm thinking it shouldn't be a problem...I hope.

 

I cannot attest for all DPs, but from what I was seeing on my ZZP one is the DP rests inside that "hump" going down the center of the car (what on a RWD car would be a transmission tunnel). As a result, my O2 on my ZZP pipe is coming out the side (does not appear to be pitched at an angle). It does not leave much room to be extended out before you run into the sheet metal for the floor pan.

End result, test fitting everything would be important. I would probably place the DP in without the O2 sensor installed at first and see how things are lining up. Keep in mind, the DP and parts of the exhaust are meant to have a little flex in them, so I certainly would not want the O2 resting right on the floor pan.

 

With all of this talk & hub-bub, has anyone used, or known/seen anyone use one of theses - O2 Emulator #10-01-00861 ?

Effectiveness as far as keeping away SES/common said code(s) as opposed to tuning out codes, anti-fouling, etc.?

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You're probably going to need a new O2 sensor on the manifold just so you know

 

As far as i have seen and read the idea of the anti fouler is so that the sensor doesn't pull a code because of theflow on some of these dp .So drilling all the way thru that put the o2 right in the exhaust and pull a code.You want enought of the exhaust to hit it and not pull a code. You can go to zzp and get a pcm for short money and the program that o2 code out and a couple others zzp is the cheaps I have come across .If you know a good exhaust guy you can angle it some.