Homebrew O2 Simulator - Simple and cheap and effective
I haven't tried this on a 5g, so don't bother asking me if it works. What I can tell you, though, is that it works on the S2k which has much pickier electronics when it comes to secondary O2 (cat) performance.
Originally posted by SLO-S2000
Ok...I got this tip from some of the local car enthusiasts...and this is one cheap O2 simulator.
It works, and there is no need to cut any wires or anything...very easy as well.
I personally have driven about 300 miles since, no CEL. So anybody who wants to run a test pipe...here is the mod you should do to stop the CEL...don't bother with the electronic ones with only some of them working...and not working all the time. These pics are from it being done STi, but I did it on my S, works just the same.
Those are the Spark plug, Anti-Foulers you'll need to do this..just pick them up at any auto parts store.
This modification effectively reduces the amount of exposure the secondary O2 has to the exhaust stream. This mod will allow the 5g and '96 4g guys to avoid the CEL for poor cat performance without having to do the dubious OBD2 "workaround" and pass OBD2-based emissions testing.
Fascinating . . . . But I'm not sure I completely get it. The two non-foulers are installed in the original O2 bung, and then the O2 sensor installs in them, right? So what do you need to bore out?
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Since the anti-fouler is intended for a spark plug, there is not enough clearance for the O2 sensor tip. I would encourage people to NOT trust the instructions and measure the tip of your O2 sensor (they do vary) and drill according to that.
I am not entirely certain that all of this is necessary or that there isn't a better way to do it. I'm going to take a crack at it and see if there's a way to improve on it.
Hmmm... just attempted this homebrew idea. Lemme give a real quick background:
I had Mugen Headers and Greddy EVO. To finish it off, I got a carsound 2.5" cat. Upon installing the highflow cat, my original o2 sensor(aftercat) was stuck in the old cat so I bought a new bosch universal. Low and behold, I get CEL code 67 (catalyst system below threshold) and after some searching on po.com, someone suggested changing the precat o2 so that the before and after cat o2 sensors get similar readings due to both being new. Bought a new Walker precat o2 sensor and my CEL would light up about every 200miles of driving (same code). Each time it would light up, I'd just reset the ECU and say skrew it.. til I just got tired of doing that. So I decided to give this a try:
First off: contrary to the s2000 example picture given above, in my case the o2 bung on a 5thgen prelude is tilted more upwards. Putting spark plug non foulers would cause the o2 sensor (wire end) to not have enough clearance between the bung and the exhaust heatshield (the huge hunk of heatshield that goes all the way to the back of the car). So I trimmed a portion of that....
Second: Only 1 nonfouler would fit due to clearance. Even if you trim the heatshield away, there's still a deadend behind it.
Third: I used the 42009 (i think) nonfouler as it bolts directly into the o2 bung as well as the o2 sensor, and bored that. I had to use progressively larger drill bits until I finally reached the 1/2" size (I wish I had a drill press). The 1/2" drill bit is probably the largest you could go into the 42009 nonfouler without "boring" right through to the outside thread (hard to explain but trust me). At 1/2" boring, the Bosch sensor (remember I'm doing the aftercat o2) head BARELY fit into the nonfouler. I'm talking about MAYBE 1mm clearance around the head if even that. Notice in Daemione's post above, the universal o2 head is not only longer but thicker than an OE piece.
I dont know if that's gonna restrict any of the o2 sensor's ability to read the aftercat exhaust fumes, but I took it around for about 30miles with no CEL. I'll probably come back to give updates in a couple weeks. If there's ppl interested in doing this and want pix, I could take some, but lets wait and see what happens first.
I haven't dealt with a car with a cat in so long... all the vehicles I deal with that have test pipes should be able to clear, no problem. I would think that, especially if you have a cat of any type, one non-fouler should be enough.
With the homebrew, I was able to drive approximately 300miles without CEL. Too bad I spun a bearing at a track event or I would've had at least 1kmiles to verify it works
Thanks for the heads up Marcucci You just saved me 70 bucks. I was just about to purchase the O2 simulator from Casper's Electronics which I was very skeptical about. It only took me about a half hour and 10 bucks (5 for the non-foulers and 5 for the 1/2" drill bit) to tackle. There was a clearance issue so I had to pound the heatshield a bit. Other than that it was very simple and inexpensive to do. We'll see how long it'll last
...in my case the o2 bung on a 5thgen prelude is tilted more upwards. Putting spark plug non foulers would cause the o2 sensor (wire end) to not have enough clearance between the bung and the exhaust heatshield (the huge hunk of heatshield that goes all the way to the back of the car). So I trimmed a portion of that....
Only 1 nonfouler would fit due to clearance. Even if you trim the heatshield away, there's still a deadend behind it.
...but I took it around for about 30miles with no CEL....
So in the Prelude's case, having only one of two nonfoulers can still avoid throwing a CELL on any type of cat. What about a test pipe if clearance is still an issue?
BTW Do you have a 5TH GEN and can you take pictures of this Homebrew? I'd like to see this "deadend".
EDIT.
Quote:
Originally Posted by 619_sdeuce
um... no don't try it with just one non fouler... I did it and it did not relocate the o2 sensor far enough out of the direct path of the exhaust and I threw a CEL right away... changed it back to using both of the non fouler pieces and everything was fine...
The deadend I am referring to is simply the underside of the car's floor board. For a high flow cat that throws CEL, one fouler should be enough. For a testpipe, I'd have no idea.
Keep in mind though, that 619_sdeuce's case is for an S2k, which emissions are way more strict than the prelude.
I just got my car back so I can take pix sometime in near future. Gluck
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At that price, it's definitely worth a shot.
You just saved me 70 bucks. I was just about to purchase the O2 simulator from Casper's Electronics which I was very skeptical about. It only took me about a half hour and 10 bucks (5 for the non-foulers and 5 for the 1/2" drill bit) to tackle. There was a clearance issue so I had to pound the heatshield a bit. Other than that it was very simple and inexpensive to do. We'll see how long it'll last 
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