BrokenProjectGT Posted February 21, 2020 Share Posted February 21, 2020 Hello All! I've been doing some research in trying to disable the rear O2 sensor on my Legacy GT. I was following a couple of posts on the romraider forum about using IDA to adjust the XML file but keep hitting a wall when trying to figure out exactly what to do. I search for the values mentioned in the post but can't find the values or any further direction on what to do. Looking at my car's rom (A2WC510N), I noticed that it had three closed loop fueling tables. CL Fueling Target Compensation (Load) CL Fueling Target Compensation A (ECT) CL Fueling Target Compensation B (ECT) I did more research on these tables and it seems these might be related to the rear O2 sensor. A few posts that I read mentioned about zeroing these tables would disable your rear O2 sensor. I'm not sure if it means just adjusting ALL the values on the table to 0 or just certain range values. I also saw another post mentioned setting all the values to -.0001 or something along those lines to basically disable the rear O2 sensor. Can anyone point me in the right direction? Feel free to correct any of my misinformation and pardon my newbie-ness as I'm learning as I go. Link to comment Share on other sites More sharing options...
GEE-OTTO Posted February 21, 2020 Share Posted February 21, 2020 Why do you want the rear O2 disabled? Are you trying to disable the P0420 code? Link to comment Share on other sites More sharing options...
awfulwaffle Posted February 21, 2020 Share Posted February 21, 2020 (edited) Why do you want the rear O2 disabled? Are you trying to disable the P0420 code? Removing the rear O2 and not disabling the closed loop fueling target will cause your car to idle/cruise at like a 13.5-14 AFR and tank your gas mileage. OP: I was unable to figure out how to do it OpenSource (though I didn't try very hard), so I just plugged in a rear O2. None of the tables you listed have to do with the rear O2 closed loop fueling compensation. The correct table wasn't available by default in Romraider for me last I looked. Maybe I'll dig into it in my free time when I have some, wouldn't hurt to figure out in order to have that channel available for datalogging. Edited February 21, 2020 by awfulwaffle Link to comment Share on other sites More sharing options...
BrokenProjectGT Posted February 21, 2020 Author Share Posted February 21, 2020 The reason I'm looking for a method of disabling the rear O2 sensor on the ECU is because my car has a weird surging effect and A/F #1 correction oscillation when in cruising RPM's around the 2k to 3k. The car has a TD04 turbo and the front O2 sensor was moved from the up pipe to the down pipe. Further research shows that moving the front O2 to the down pipe tends could possibly cause this issue since USDM ECU expects the O2 sensor to be in the up pipe and not further down. I've tried looking for anything that I can adjust related to A/F #3 on the rom using romraider but can't find anything which is why I decided to ask about the CL fueling target tables when I ran into this post while doing more research. I also tried following this post to see if I was able to adjust A/F #3 but I'm not able to find the values. Post from a couple years ago from user "unclemat": "The ongoing issue I had with twinscroll tune was a constant oscillation on steady throttle around 3k rpm. I think it has to do with the remote relocation of the front O2 sensor. I hope that zeroing AF3 correction limits (see this romraider thread) may help. For me the only way to eliminate this oscillation was to actually disconnect *rear* O2 sensor. " I was considering just unplugging the rear O2 but read that it would cause the car to run in open loop all the time. Now I know what some of you are thinking. Maybe it's a vaccuum/boost leak, injectors, gasoline, etc. I have gone through all that. Had injectors cleaned and flow tested, replaced intake manifold gaskets, replaced PCV, replaced and secured all vacuum line, smoke tested to make sure no leaks, tested using a brand new MAF, replaced air filter, tested the fuel pressure, new coils, new spark plugs. I even went as far as flashing the stock rom back on the car to see if it was an issue with the tune. I nearly gave up on trying to fix this when I ran into information that it could possibly be the rear O2. The P0420 code is already disabled on the ECU but I'm guessing that the rear O2 is still processing information regardless of the code being shut off. Once again, thanks for the help!! Link to comment Share on other sites More sharing options...
Berge56 Posted February 24, 2020 Share Posted February 24, 2020 Your o2 sensor should be in your header and not in your downpipe. I would get the o2 installed in the correct position, leave your rear o2 sensor hooked up as it gives your front o2 sensor feedback. It sounds like you need to have your car tuned and I would highly suggest taking it a professional as it's not worth trying to figure it out on your own. These engines are sensitive and bad tunes can lead to a bad motor fast. Link to comment Share on other sites More sharing options...
bugblatterbeast Posted April 11, 2020 Share Posted April 11, 2020 Removing the rear O2 and not disabling the closed loop fueling target will cause your car to idle/cruise at like a 13.5-14 AFR and tank your gas mileage. OP: I was unable to figure out how to do it OpenSource (though I didn't try very hard), so I just plugged in a rear O2. None of the tables you listed have to do with the rear O2 closed loop fueling compensation. The correct table wasn't available by default in Romraider for me last I looked. Maybe I'll dig into it in my free time when I have some, wouldn't hurt to figure out in order to have that channel available for datalogging. IIRC, you need to zero both the learning and correction limits for AF3. Link to comment Share on other sites More sharing options...
m sprank Posted April 13, 2020 Share Posted April 13, 2020 Start with moving the O2 sensor to the header collector. The OE O2 is not a wideband. Link to comment Share on other sites More sharing options...
JT1657616149 Posted April 14, 2020 Share Posted April 14, 2020 he is most likely twin scroll which is why his front o2 sensor is in the downpipe and not the manifold. Link to comment Share on other sites More sharing options...
m sprank Posted April 14, 2020 Share Posted April 14, 2020 Seen it it more than a few Subies that were not twin scroll. Twin scroll set up are more and more rare as well. Expensive and they offer no real gains. Link to comment Share on other sites More sharing options...
JT1657616149 Posted April 15, 2020 Share Posted April 15, 2020 Agree to disagree. Link to comment Share on other sites More sharing options...
BrokenProjectGT Posted April 16, 2020 Author Share Posted April 16, 2020 @JT is correct. It is a twin scroll setup and the OEM JDM header does not have an O2 bung. I've came to the conclusion that there's no way around this other than having to weld a bung into the headers which I'm planning to do sometime this upcoming weekend. Though, the sensor will only be monitoring two cylinders which brings up slight concern. Link to comment Share on other sites More sharing options...
m sprank Posted April 17, 2020 Share Posted April 17, 2020 Go all out and go after market ECM (like an AEM Infinity) and run 4 wide bands, one for each cylinder. There is a reason Subaru gave up on the twin scroll set up. But, you might enjoy the experience of learning through doing. Link to comment Share on other sites More sharing options...
Guest Posted April 2, 2021 Share Posted April 2, 2021 Zeroing AF3 correction limits gets rid of the oscillation. You'll find more info here: https://www.romraider.com/forum/viewtopic.php?f=40&t=8131 Link to comment Share on other sites More sharing options...
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