Do NOT remove your rear O2 sensor - Page 3

Nixlimited · 07-24-2006, 08:17 AM

Hmmm. I have just had my rear 02 removed for an innovative LC-1. I think I have experienced a bit of what you all are talking about, but my idle seems to be 14.7ish fairly consistently. I do have some cruise AFR issues though.

Nixlimited · 08-22-2006, 04:07 PM

OK, here is something interesting. With a protune I didn't have this problem at all, but with a ST I definitely have the 13.8 AFR target issue.... Seems like there is different logic between the two.

benton0311 · 09-24-2006, 07:26 PM

Had to revive this one...

Just experienced the same thing. A while ago I would have told anyone who said that removing the rear O2 with the codes disabled had any effect on A/F ratio that they were full of s**t.

Sure enough I disable all codes in my rear O2 except for the heater and clamp it to the side of the transmission/DP mount. No probs, no codes. Placed my wideband in the rear bung. Everything seems cool until I drive to the beer store and it's reading high 13's. Grab some beer and go home and it's back into the 14's. So I drive it some more and it wants to target mid-high 13's and then sometimes it wants to be back at stoich.

What's perplexing me is why. It's obvious that the rear O2 can't be used for A/F tuning. There are codes for post catalyst fuel trim system rich and post catalyst fuel trim system lean (P2097 and P2096 respectively). I knew of the slow response and inefficiency codes as well as heater circuit codes which make sense. But to re-adjust A/F ratio based on a more or less on/off rear O2 doesn't make sense. Also, things seem to be fine with a resistor fix (won't pass emissions "not ready") and mechanical CEL fix (two antifoulers - will pass with flying colors - not that I've done that)

So, why go rich in the apparent absence of cats? If anything, if there were cat issues then richer would foul the cats more.

WolfPlayer · 09-25-2006, 04:21 AM

I don't know either. But, at least you are now aware of the truth of the matter

I am actually running a mechanical fix and things seem good ('HELP!' anti-fouler and am only running it because the threads on my O2 were damaged and I didn't want to put damaged threads into my APS TBE).

Fact of the matter is that Subaru does use the rear O2 to fine tune the AFRs. I don't know why. But it is true.

I think the ECU is making it richer because of too much oxygen. If you tie your O2 sensor out of the way then the signal will read too much oxygen. I believe the same to be true if you just unplug it (because you get 0mV and that is infinitely lean).

The flip side to all of this is that if the Rear O2 sensor sees things too rich during normal driving, then I hypothesize that the ECU will lean things out a touch and this will extend the life of the catalytic converters.

t

benton0311 · 09-25-2006, 10:42 AM

I guess I'm wondering if it is actually using it fine tune AFRs, which doesn't seem likely, or adding fuel because of what it thinks is a malfunction of some sort due to exhaust leak, missing cat, etc.

I really don't think the rear is accurate enough for fine tuning, especially when compared to the front. I would have to speculate that is changing AFRs because of seeing what it thinks is a super extreme lean condition and adding fuel to compensate regardless of what the front O2 says. I just don't think it can fine tune - only compensate when it sees one drastic extreme or the other. This would seem to be supported by being able to run a mechanical fix and even a resistor fix with no problems (resistor just won't pass the OBDII diagnostic query but won't throw a code).

Of course, this is just my best guess. I can tell you one thing: there is such a thing as over-engineering (K.I.S.S.). Stand-alone is looking better and better every day.

pj21086 · 10-15-2006, 07:37 PM

My LC-1 and XD-16 should be here and i was wondering what would be the best location for the wideband 02 sensor. I was planning on getting a bung welded into the lower end of the dp away from the turbo but since the car's o2 sensor is located in the headers, wouldnt that be the best location? How much of an effect would exhaust leaks have on the accuracy of the wideband?

WolfPlayer · 10-15-2006, 07:39 PM

Put it where you originally thought ... in the downpipe but away from the turbo. The closer to the turbo the more abuse it will take and thus the sensor won't last as long. Don't put it pre-turbo. There is too much pressure in that location and pressure WILL affect your AFR readings.

Now, with all of that said, I have my wideband directly after the turbo (in the O2 port in the APS high flow turbo outlet).

t

Toophless · 10-26-2006, 07:59 AM

I run the resistor fix in the rear O2's blue wire (1 Megaohm) so it does not read what it should, but it won't throw a code. I also ran the AP with the codes deleted by the stages, now running my Enginuity flash with the codes defeated. But I'm curious now about removing the resistor to see if anything changes. All of this is under a UTEC as well.

Contrary to popular recommendations, I run my W/B sensor (Tuna-pro) in the up-pipe. It has lived there as long as any sensor has survived in any location, and its accuracy, (derived by noting the occasions that I've tuned too lean and get mild knock counts... "yup, should knock there") seems to be just fine. The stocker is in that same exhaust flow anyway.

I used to run the O2 in the DP about 6" past the bellmouth, where temps ran ~900 F, and it was shielded by the innovate-motorsports bung-extention. Now it is in 1100F and up temps and is living... no heat shield at all.

Not saying its the best place. I just don't think they are quite as finicky as people think. Keeping fingerprints off of them, not letting them dangle... basicly just installing them and leaving them alone is my policy.

WolfPlayer · 10-26-2006, 09:06 AM

^^^ Totally depends on the WB Unit. The LC-1 will shutdown and not operate in that environment. The LC-1 monitors temps and will set an error code. Been there - done that

t

Christian. · 10-26-2006, 09:16 AM

Quote:

Originally Posted by WolfPlayer

^^^ Totally depends on the WB Unit. t

Agreed, you should read the technical papers on the various HEGO, WB Lambda sensors, some are pressure sensitive (most WBO2s are). Being in the Up-pipe would provide an environment of higher pressure than that behind the turbine outlet; this will skew the sensors reading.

Take care,
Christian.

LukeSkyWRX · 12-25-2006, 04:57 PM

bingo, Christian is correct.

O2 sensors use a difference in partial pressure of oxygen between the exhaust and the ambient air. this is done by taking a piece of yittrium doped zirconia and mesuring the voltage potential created by the oxygen pressure difference. the Yitrium creates oxygen vacancies in the lattice that allow for the oxygen to move through the zirconia. the diffusion of the O2 is dependent on the partial pressures and the temperature, that is why most aftermarket O2 sensors are heated because they are ment to be run further down the exhaust stream than the stock sensors. and they cant extract enough heat from the exhaust to run effectivly.

Zirconia is a High temperature ceramic that is not hurt by the temperatures found in the exhaust stream. the same material is used in solid oxide fuel cells that run at 1000 deg C for decades at a time with no issues. in this case heat is a good thing because it makes the diffusion of O2 faster, removing lag in A/F changes.

close to the turbine exit as possible is the most ideal location for a sensor of this type. but manufacturers vary how they do things so here is a grain of salt.

luke

O6STi · 01-04-2007, 10:00 PM

My AFR's before a Stock ECU (red)and after a ecutek reflash(blue). This was runninig catless and without rear o2 sensor.

CryFarKilla · 01-04-2007, 10:18 PM

just out of curiosity because of ur name 06sti, my 06 only has one 02 sensor am i wrong? i mean i put the TBE on and there was only ONE but because of your name and because of your reply its confusing my noob a s s....LOL

JASON

O6STi · 01-04-2007, 10:38 PM

TBE only has one post cat. But there are others. When you move on from your noob status. You will go into the drak world of headers. There you might find more...

daemon · 01-05-2007, 05:42 AM

Quote:

Originally Posted by CryFarKilla

my 06 only has one 02 sensor am i wrong?

There are two. The primary one used by the ECU is in the exhaust manifold near the passenger front wheel. It is the second O2 sensor in the TBE that is the one primarily being referred to in this thread. It was generally assumed it was useless for anything other than confirming the cats were working. So if you had a fix (ECU or otherwise) to stop the CEL related to it, then it seemed that you could just get rid of it altogether.

07-24-2006, 08:17 AM	#31
Nixlimited Professional STI Racer Car: 05 STi CGM Fav Mod: Tuning... Location: San Diego Posts: 811 Join Date: Feb 2005 Trader Rating: (0)	Hmmm. I have just had my rear 02 removed for an innovative LC-1. I think I have experienced a bit of what you all are talking about, but my idle seems to be 14.7ish fairly consistently. I do have some cruise AFR issues though. This ad is not endorsed by this member. Please register or login to hide this ad.

08-22-2006, 04:07 PM	#32
Nixlimited Professional STI Racer Car: 05 STi CGM Fav Mod: Tuning... Location: San Diego Posts: 811 Join Date: Feb 2005 Trader Rating: (0)	OK, here is something interesting. With a protune I didn't have this problem at all, but with a ST I definitely have the 13.8 AFR target issue.... Seems like there is different logic between the two.

09-24-2006, 07:26 PM	#33
benton0311 Silver Member Car: 08 335i Graphite Fav Mod: Subaru delete Location: SW Asia/Maryland Posts: 172 Join Date: Jan 2004 Trader Rating: (0)	Had to revive this one... Just experienced the same thing. A while ago I would have told anyone who said that removing the rear O2 with the codes disabled had any effect on A/F ratio that they were full of s**t. Sure enough I disable all codes in my rear O2 except for the heater and clamp it to the side of the transmission/DP mount. No probs, no codes. Placed my wideband in the rear bung. Everything seems cool until I drive to the beer store and it's reading high 13's. Grab some beer and go home and it's back into the 14's. So I drive it some more and it wants to target mid-high 13's and then sometimes it wants to be back at stoich. What's perplexing me is why. It's obvious that the rear O2 can't be used for A/F tuning. There are codes for post catalyst fuel trim system rich and post catalyst fuel trim system lean (P2097 and P2096 respectively). I knew of the slow response and inefficiency codes as well as heater circuit codes which make sense. But to re-adjust A/F ratio based on a more or less on/off rear O2 doesn't make sense. Also, things seem to be fine with a resistor fix (won't pass emissions "not ready") and mechanical CEL fix (two antifoulers - will pass with flying colors - not that I've done that) So, why go rich in the apparent absence of cats? If anything, if there were cat issues then richer would foul the cats more.

09-25-2006, 04:21 AM	#34
WolfPlayer Moderator & ECU Tech Car: 05 CGM STI Fav Mod: mo boostaz Location: Fredneck, MD Posts: 3,542 Join Date: Jun 2004 Trader Rating: (6)	I don't know either. But, at least you are now aware of the truth of the matter I am actually running a mechanical fix and things seem good ('HELP!' anti-fouler and am only running it because the threads on my O2 were damaged and I didn't want to put damaged threads into my APS TBE). Fact of the matter is that Subaru does use the rear O2 to fine tune the AFRs. I don't know why. But it is true. I think the ECU is making it richer because of too much oxygen. If you tie your O2 sensor out of the way then the signal will read too much oxygen. I believe the same to be true if you just unplug it (because you get 0mV and that is infinitely lean). The flip side to all of this is that if the Rear O2 sensor sees things too rich during normal driving, then I hypothesize that the ECU will lean things out a touch and this will extend the life of the catalytic converters. t

09-25-2006, 10:42 AM	#35
benton0311 Silver Member Car: 08 335i Graphite Fav Mod: Subaru delete Location: SW Asia/Maryland Posts: 172 Join Date: Jan 2004 Trader Rating: (0)	I guess I'm wondering if it is actually using it fine tune AFRs, which doesn't seem likely, or adding fuel because of what it thinks is a malfunction of some sort due to exhaust leak, missing cat, etc. I really don't think the rear is accurate enough for fine tuning, especially when compared to the front. I would have to speculate that is changing AFRs because of seeing what it thinks is a super extreme lean condition and adding fuel to compensate regardless of what the front O2 says. I just don't think it can fine tune - only compensate when it sees one drastic extreme or the other. This would seem to be supported by being able to run a mechanical fix and even a resistor fix with no problems (resistor just won't pass the OBDII diagnostic query but won't throw a code). Of course, this is just my best guess. I can tell you one thing: there is such a thing as over-engineering (K.I.S.S.). Stand-alone is looking better and better every day.

10-15-2006, 07:37 PM	#36
pj21086 Senior STI Driver Car: 05 WRB STi & 07 AW 3 Fav Mod: Invidia G200 Location: Modesto, CA Posts: 334 Join Date: Aug 2006 Trader Rating: (2)	My LC-1 and XD-16 should be here and i was wondering what would be the best location for the wideband 02 sensor. I was planning on getting a bung welded into the lower end of the dp away from the turbo but since the car's o2 sensor is located in the headers, wouldnt that be the best location? How much of an effect would exhaust leaks have on the accuracy of the wideband?

10-15-2006, 07:39 PM	#37
WolfPlayer Moderator & ECU Tech Car: 05 CGM STI Fav Mod: mo boostaz Location: Fredneck, MD Posts: 3,542 Join Date: Jun 2004 Trader Rating: (6)	Put it where you originally thought ... in the downpipe but away from the turbo. The closer to the turbo the more abuse it will take and thus the sensor won't last as long. Don't put it pre-turbo. There is too much pressure in that location and pressure WILL affect your AFR readings. Now, with all of that said, I have my wideband directly after the turbo (in the O2 port in the APS high flow turbo outlet). t

10-26-2006, 07:59 AM	#38
Toophless Amateur STI Driver Car: Rhino '04 STi Fav Mod: Pistons... hood and Mahle Location: Lewisville/Clemmons NC Posts: 42 Join Date: Aug 2004 Trader Rating: (2)	I run the resistor fix in the rear O2's blue wire (1 Megaohm) so it does not read what it should, but it won't throw a code. I also ran the AP with the codes deleted by the stages, now running my Enginuity flash with the codes defeated. But I'm curious now about removing the resistor to see if anything changes. All of this is under a UTEC as well. Contrary to popular recommendations, I run my W/B sensor (Tuna-pro) in the up-pipe. It has lived there as long as any sensor has survived in any location, and its accuracy, (derived by noting the occasions that I've tuned too lean and get mild knock counts... "yup, should knock there") seems to be just fine. The stocker is in that same exhaust flow anyway. I used to run the O2 in the DP about 6" past the bellmouth, where temps ran ~900 F, and it was shielded by the innovate-motorsports bung-extention. Now it is in 1100F and up temps and is living... no heat shield at all. Not saying its the best place. I just don't think they are quite as finicky as people think. Keeping fingerprints off of them, not letting them dangle... basicly just installing them and leaving them alone is my policy.

10-26-2006, 09:06 AM	#39
WolfPlayer Moderator & ECU Tech Car: 05 CGM STI Fav Mod: mo boostaz Location: Fredneck, MD Posts: 3,542 Join Date: Jun 2004 Trader Rating: (6)	^^^ Totally depends on the WB Unit. The LC-1 will shutdown and not operate in that environment. The LC-1 monitors temps and will set an error code. Been there - done that t

12-25-2006, 04:57 PM	#41
LukeSkyWRX Amateur STI Driver Posts: 23 Join Date: Apr 2006 Trader Rating: (1)	bingo, Christian is correct. O2 sensors use a difference in partial pressure of oxygen between the exhaust and the ambient air. this is done by taking a piece of yittrium doped zirconia and mesuring the voltage potential created by the oxygen pressure difference. the Yitrium creates oxygen vacancies in the lattice that allow for the oxygen to move through the zirconia. the diffusion of the O2 is dependent on the partial pressures and the temperature, that is why most aftermarket O2 sensors are heated because they are ment to be run further down the exhaust stream than the stock sensors. and they cant extract enough heat from the exhaust to run effectivly. Zirconia is a High temperature ceramic that is not hurt by the temperatures found in the exhaust stream. the same material is used in solid oxide fuel cells that run at 1000 deg C for decades at a time with no issues. in this case heat is a good thing because it makes the diffusion of O2 faster, removing lag in A/F changes. close to the turbine exit as possible is the most ideal location for a sensor of this type. but manufacturers vary how they do things so here is a grain of salt. luke

01-04-2007, 10:00 PM	#42
O6STi Junior STI Driver Car: www.boosted-subie.co Location: Free Subie Pic Hosting Posts: 121 Join Date: Aug 2006 Trader Rating: (0)	My AFR's before a Stock ECU (red)and after a ecutek reflash(blue). This was runninig catless and without rear o2 sensor.

01-04-2007, 10:18 PM	#43
CryFarKilla Senior STI Driver Car: 2006 Subaru STI Fav Mod: APS 3" TBE Location: Cali Posts: 350 Join Date: Sep 2006 Trader Rating: (1)	just out of curiosity because of ur name 06sti, my 06 only has one 02 sensor am i wrong? i mean i put the TBE on and there was only ONE but because of your name and because of your reply its confusing my noob a s s....LOL JASON

01-04-2007, 10:38 PM	#44
O6STi Junior STI Driver Car: www.boosted-subie.co Location: Free Subie Pic Hosting Posts: 121 Join Date: Aug 2006 Trader Rating: (0)	TBE only has one post cat. But there are others. When you move on from your noob status. You will go into the drak world of headers. There you might find more...