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Discussion Starter · #1 ·
Ok, I have gone turboback, and am not using the rear o2 sensor. Not suprisingly, I got the CEL which I am sure would be both for the cat ineffeiciency and the slow response/defective sensor. Now, I have done a search on this topic and found out about the resistor AND capacitor mod (1Megaohm resistor with a 1microfarad capacitor), and this seemes to work well for those who still had the o2 sensor installed in their turboback exhausts. My question is this...

What resistor and Capacitor ratings should I be using if I do not want to run the rear 02 sensor at all? Any schematics that you can provide would be greatly appreciated.

I would have simply used the resitor and capacitor mod, but I do not want to go splicing into my 02 sensor wires because I want to keep everything looking as stock as possible for when I swap my stock exhaust back on for emmisions testing/warranty work. The dealer would not look to nicely on me cutting and splicing into the car's wiring.

PLEASE help me out guys...

:(
 

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Discussion Starter · #3 ·
is2scooby said:
I purchased the PEP MIL Eliminator and it works WONDERFULLY with my TXS catless race pipe. You splice into the O2 sensor's wiring, and not the car's wiring in this case. Give it a look at:

http://www.ponyexpressperformance.com/wrxmileliminator.html
Thanks for your response! My problem here is that I was unable to get a bung mounted for the 02 sensor (since I had to lie to the muffler shop that the exhaust was for track use only), so what I did was to get a Male plug identical to the one that comes on the 02 sensor. I then plan to hook up the resistor/capacitor to it. I would then plug the whole lot back into the Female plug on the car to get rid of the CEL. But my question is what kind of resistor do I need to take the place of the 02 sensor???:confused: :(
 

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I'm not sure that you can just completely eliminate the O2 sensor and replace it with a resistor (I may be wrong and there may be a fix, but it would be hard to do IMHO).

The O2 sensor in this case is a voltage generator, so the ECU must see a varying voltage signal coming back from the O2 sensor that is similar to the what it sees at the front O2 sensor (differing slightly due to the fact that it's supposed to be after a catalytic converter).

I think the best idea would be to get the O2 sensor bung welded onto the pipe and install a MIL eliminator like the PEP... I got mine welded on for $25 at a local muffler shop, however YMMV as there are no emissions laws enforced in Hawaii (yet).

Good luck!
 

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P.S. Regarding the resistor to replace the sensor, are you sure that you're not thinking about the no EGT sensor in the uppipe resistor mod rather than the rear O2 sensor MIL eliminator?

They both deal with sensors being removed/modified and CEL lights fixed with resistors... Just a thought. :)
 

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Discussion Starter · #6 ·
is2scooby said:
P.S. Regarding the resistor to replace the sensor, are you sure that you're not thinking about the no EGT sensor in the uppipe resistor mod rather than the rear O2 sensor MIL eliminator?

They both deal with sensors being removed/modified and CEL lights fixed with resistors... Just a thought. :)
Yes, I am sure. It seems that the guys on the Pontiac Granprix forums are able to install some kind of resistor totally bypassing the o2 sensor. I beleve they are commercially available (I think!), but I do not know much about them. Perhaps I will have to resort to finding a muffler shop to install my o2 sensor. But the question is, will I still have to deal with a CEL after I get this done... I still have the original cat in the uppipe left on the car right now.... Will that be enough to keep me CEL-free, or will I still need to get the resistor mod done as well?
 

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I believe to be totally CEL free you're going to have to get the O2 sensor welded into the catless pipe AND run the MIL eliminator with just the uppipe cat left in the car.

I'd like to get more info. on that resistor-fix you mention the Pontiac guys have had good luck with! Sounds interesting. Keep us posted! :)

BTW - when I was running catless EXCEPT for the high-flow cat in my midpipe (before I installed the race pipe) I was totally CEL free for more than 2,500 miles...

However I've read that the cat in the uppipe is really a "pre-cat", made more to pass cold start emissions tests while the main catalytic converters are still warming up.

Again, all just theory here... It'll be fun finding out! :D
 

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Building Mil Eliminators
We know that after the cats the mixture should be lean (because the cats function is to burn up any excess fuel that the engine did not) so all we have to do is make the Output Signal sense a low voltage (under 300mv) reading and oscillate the reading to make it look like a working o2 sensor. This can be done via the following painfully simple circuit:
I'm not sure what kind of circuit it would take to get the voltage output of the o2 sensors mimicked and sent to the ECU but I think it might be a lot easier to get the O2 bung welded into the pipe and splice in a PEP MIL Eliminator kit (or build your own, or find another type of low-pass filter out there) than installing an "O2 Simulator"... IMHO of course.

The above quote was found here: http://www.zx2racing.com/mods/mods_mil.htm
 

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Discussion Starter · #12 ·
Ok, I got the o2 sensor installed into the DP today, AND I performed the resistor/capacitor mod. No luck. The CEL is still there. My mechanic said that the resistor mod is probably working, but the fact that I had been running without my rear o2 sensor would have caused a 'hard' CEL that cannot be removed simply by disconnecting the battery and standing on the brakes. He said that he would have to connect his diagnostic equipment and mannually turn off the CEL to 'reset' the ECU. We will do this tomorrow since we ran out of time today.

Does this make sense? Does the ECU actually remember some CEL's even though you disconnect the battery and stand on the brakes???:confused:
 

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I don't think that it's possible for the ECU's in our cars to "remember" anything once power has been cut.

I'd drive the car through some more on/off cycles and miles before going through any more trouble.

When you started the car was the CEL illuminated or did it take a while for it to come on?

I had a HARD CEL for cat inefficiency on for almost a week before getting the rear O2 sensor re-installed and the PEP MIL eliminated wired into the o2 sensor.

I started the car and ran it through 3 cycles and the CEL was gone.

Drive the car some more before tinkering with it and the CEL should go off on it's own.

The computer just needs to be sure it can believe what it's "seeing" (the O2 sensor suddenly being present again and sending a proper signal). Once it goes through a couple of on/offs (the ECU) it should figure out all is well and extinguish the CEL...
 

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Discussion Starter · #14 ·
When I restarted the car, the light was there just as it was beofoe I reinstalled the o2 sensor. We tried resetting twice with no luck. The CEL was just there, and stayed on as soon as I started the car. My mechanic did not solder the resistor and capacitor into place yet as he wanted to pull the code first to see what was going on...

What I did do last night was to take the long way home, hoping that the CEL would go out by itself. I stopped to buy gas on the way home, and the CEL was still there when I started up again. I even made a few 'runs' at close to WOT to se if it would go out, but no luck... I am just a little confused right now....:(

Unfortunately, with all of the resetting that we did yesterday, my alarm system lost all of it's settings, and now needs to be reprogrammed. Unfortunately, I do not have the mannual with me here at uni:mad:
 

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Discussion Starter · #15 · (Edited)
OK, my mechanic pulled the coe yesterday from the ECU and got P0120. He though that this had to be incorrect because his scanner only had up to the 2000 Model Year Impreza. We both agreed that that resistor that we had installed must have been too great a resistance (1.0 Mega Ohms). We will try 1 kilo ohms and 2.2 kilo ohms both in 1/2 watt. Should that do the trick???Any other suggestions???
 

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Discussion Starter · #17 ·
Yeh, I kinda wanted to make my own fix for cheaper than what they are selling theirs for. I highly doubt that they will part with the information as to the ratings of the resistor and capacitor that they use in their fixes...
 

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Jigga wrote:

Yeh, I kinda wanted to make my own fix for cheaper than what they are selling theirs for. I highly doubt that they will part with the information as to the ratings of the resistor and capacitor that they use in their fixes...
Man, you're cheap!!!

Buy a PEL eliminator then.. About $20. I have one you can buy. PM me!

misterx
 
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