Do NOT remove your rear O2 sensor - Page 2

jays05 · 06-15-2006, 05:05 AM

After reading the post by R4ND0M_AX3 I can confirm that I see the same thing. I really only notice it when idling. It stays at 13.9 AFR for 15-20 seconds and then drops down to 14.7. I disconnected the rear o2 before I had the XD-1 AFR gauge so I never never noticed the change and actually thought it was normal.

WolfPlayer · 06-15-2006, 07:00 AM

Cool. Well, not cool ... but cool because 3 of us have confirmed that we all experience this unusual rich phenomena and all 3 of us removed the rear O2. When I reinstalled my rear O2 sensor things went back to normal. If one of you guys could try that then that would pretty much seal the deal (as if it isn't already).

t

daemon · 06-15-2006, 07:13 AM

Wonder if it is electrical or computational in nature. If the sensor is still plugged into the electrical connector but not installed in the pipe, would the issue still occur? Is the ECU doing some sort of difference calc on the front vs. rear reading or does it just want the circuit connected?

jays05 · 06-15-2006, 07:33 AM

I was also wondering if this was an electrical problem vs ecu logic. I won't have time to get under the car to hook back up the rear o2 till next weekend.

R4ND0M_AX3 · 06-15-2006, 07:42 AM

I don't yet have an extra bung for both the wideband and stocker.

sebtarta · 06-15-2006, 07:42 AM

Wolf did you try leaving the connector of the O2 connected and place the wideband where the O2 goes? Just zipt tie the O2 somewhere and go for a test, leaving the O2 connected.

WolfPlayer · 06-15-2006, 07:51 AM

Quote:

Originally Posted by sebtarta

Wolf did you try leaving the connector of the O2 connected and place the wideband where the O2 goes? Just zipt tie the O2 somewhere and go for a test, leaving the O2 connected.

I thought about doing that but, honestly, it's not a solution so I just went back to normal (because I had my plate full with a bunch of other stuff I was doing to the car). Fact is, leaving an O2 open and exposed to the elements like that will destroy it.

Admittedly, it is a good test though. I just didn't have the time to do it. Easy enough to do this test though. Just pull the rear O2 out, tie it out of the way, put a plug in the pipe, and then go for a drive.

t

jays05 · 06-15-2006, 07:54 AM

Quote:

Originally Posted by R4ND0M_AX3

I don't yet have an extra bung for both the wideband and stocker.

Me neither, I was just going to let the rear o2 hang and see what happens.

STirish · 06-15-2006, 07:56 PM

Quote:

Originally Posted by WolfPlayer

I have heard it from a few people that it is totally cool to remove the rear O2 sensor on a Cobb Stage 2 so that you can utilize that location for a wideband. I have my wideband in the bung located on the APS high flow turbo outlet, aka HFTO (downpipe for those not familiar with the APS). This puts the wideband very close to the turbo and thus, the wideband gets REALLY hot. Such extreme heat decreases the wideband's longevity. Fast forward to yesterday when I was replacing all the gaskets in my TBE due to what I thought was a leak (turned out not to be). Anyhow, PERFECT time for me to remove the wideband from the APS HFTO and put it in the rear location. Cool. So, I completely removed the rear O2 sensor, taped the plug, and relocated my wideband to that rear location. Started the car and drove it around. No CELs - wideband reads normal - car feels fine. Woohooo! ... .. . or so I thought. Brought up the realtime data view and observed the stock AFR and my wideband AFR. Whoa. This is weird. Becomes very apparent that the ECU doesn't appear to be shooting for 14.7 anymore. Rather, it seems to be shooting for slightly richer ... 14.4-14.5 or so. Furthermore, when you let off the gas the AFR goes rich to ~13.5 and stays there. Very weird. I remembered a post by R4ND0M_AX4 awhile ago and he had these exact same conditions (http://www.wrxforum.com/cgi-bin/ulti...;f=14;t=000043). I thought it was weird at the time and never was able to reproduce it, and therefore, forgot about it. Well, I just reproduced it. Yick.

So, this morning I put the wideband back where it was and hooked the rear O2 sensor back up. Everything went back to normal. AFRs focused at 14.7 and when letting off the gas it did not go to 13.5AFRs. Yay!

Moral of the story, don't unhook the rear O2 sensor. Apparently there is some trigger in the code that will target different AFRs if this sensor is unplugged.

t

I believe there is a way to tie in the wideband O2 and have it act like the stock narrow band so you can make the car happy. Hmmm, don't remember the details, but it was in the LC-1 manual.

R4ND0M_AX3 · 06-16-2006, 08:33 AM

Quote:

Originally Posted by STirish

I believe there is a way to tie in the wideband O2 and have it act like the stock narrow band so you can make the car happy. Hmmm, don't remember the details, but it was in the LC-1 manual.

We used to do this for the older Hondata ECU tuning. We had to also use resisters to keep the O2 Heater circuit happy.

reid-o · 06-17-2006, 11:07 AM

I don't normally keep my wideband connected and installed 24/7, preferring to remove it after datalogging, as I'm a tightwad, and I don't like buying new sensors.

Normally, i just remove the rear o2 and replace it with the WB sensor, keeping the rear o2 tucked out of the way while I'm logging and replacing it when I'm done.

Today, I installed Dynotune's digital A/F gauge for the LC-1 permanently.
http://www.dynotunenitrous.com/store...lver-large.JPG
It's pretty cheap, and except for the cheesy Dynotune label, the display is at least red and blends into the STI gauges acceptably but not well.

I kept the rear 02 connected and zip tied out of the way, and I don't see the rich condition you are all seeing.
The sensor reading must not be so important, but the ECU must be looking for the heater circuit.

I know that leaving an 02 to open air will eventually kill it, but I'm wondering if my solution is long term.
When an 02 sensor dies, does the heater element short out along with it?
I don't mind leaving the heated sensor exposed, and I don't mind the sensor itself going south and reading innacurately, since I don't have a cat, and we don't have emission inspections here in Hawaii, so long as it won't short out the 5v heater circuit.

The reakly easy way would be to remove the downpipe and just tack another bung on the other side of the pipe in there, and I may do that later if and when I upgrade the turbo, since I'll have the downpipe off, but I'm lazy and just want to know if anyone wouldn't do this.

crystal_Imprezav · 06-23-2006, 12:25 PM

Has anyone tried the PLX M-300 wideband that has the narrowband analog outputs that can trick the ecu into believeing the stock o2 is still there. I too do not have an extra o2 bung and was about to order the LC-1 until I saw this feature on the PLX. I wonder if you hook up the PLX wideband sensor and run the analog wires down to the stock o2 sensor harness and hook it up there if the car will act as normal. Anyone try this or something similar? Cobb maybe since I know you guys are using the PLX wideband?

R4ND0M_AX3 · 06-23-2006, 03:58 PM

The LC-1 (and LM-1) has the analog outputs that can be configured as a stock sensor also.

There are two 0-5V analog outputs. I think the first one is already setup like a typical narrowband.

Merchgod · 06-24-2006, 06:27 AM

The rear O2 sensor is used to make additional small changes to closed loop fueling. I have my rear O2 still installed in my WRX with the mechanical extender and my ECU explorer logs occasionally show it pulling less than 1 percent of fuel. Not sure if ST logs show the rear o2 correction, but ECUexplorer shows it as the parameter A/F Correction #3.

I'm guessing that with Cobb's extended threshold for rear o2 failure, perhaps the ECU, which would normally throw a CEL and ignore the rear o2 if it saw no signal, is now considering the non-signal as a super lean condition post-cat and using the maximum authority allowed by a "functioning" rear o2 to richen the mixture in closed loop.

crystal_Imprezav · 07-17-2006, 07:24 AM

BTW just as an update, I zipped tied my o2 sensor as well to the tranny brace to run my lc-1 and it did exhibit the same rich closed loop conditions you all are seeing. 13.8 while cruising at part throttle and 14.3 when at a stop for a couple of seconds until it goes back up to 14.7. Got my o2 bung welded into my DP yesterday and stuck the stocker back into its place and the wideband into its new bung and wah-lah AFR's back to 14.7 at part throttle and at a stop. FWIW I didnt get a CEL for over 2 weeks with the sensor tied up until I was about 10 miles from the shop. Just an update for the thread.

06-15-2006, 05:05 AM	#16
jays05 Spec C Club Fav Mod: when it's not blown up Location: Upstate NY Posts: 1,470 Join Date: Nov 2004 Trader Rating: (0)	After reading the post by R4ND0M_AX3 I can confirm that I see the same thing. I really only notice it when idling. It stays at 13.9 AFR for 15-20 seconds and then drops down to 14.7. I disconnected the rear o2 before I had the XD-1 AFR gauge so I never never noticed the change and actually thought it was normal. This ad is not endorsed by this member. Please register or login to hide this ad.

06-17-2006, 11:07 AM	#26
reid-o Senior STI Driver Car: 04 Black STI Location: Mililani Hawaii Posts: 322 Join Date: Dec 2005 Trader Rating: (3)	I don't normally keep my wideband connected and installed 24/7, preferring to remove it after datalogging, as I'm a tightwad, and I don't like buying new sensors. Normally, i just remove the rear o2 and replace it with the WB sensor, keeping the rear o2 tucked out of the way while I'm logging and replacing it when I'm done. Today, I installed Dynotune's digital A/F gauge for the LC-1 permanently. http://www.dynotunenitrous.com/store...lver-large.JPG It's pretty cheap, and except for the cheesy Dynotune label, the display is at least red and blends into the STI gauges acceptably but not well. I kept the rear 02 connected and zip tied out of the way, and I don't see the rich condition you are all seeing. The sensor reading must not be so important, but the ECU must be looking for the heater circuit. I know that leaving an 02 to open air will eventually kill it, but I'm wondering if my solution is long term. When an 02 sensor dies, does the heater element short out along with it? I don't mind leaving the heated sensor exposed, and I don't mind the sensor itself going south and reading innacurately, since I don't have a cat, and we don't have emission inspections here in Hawaii, so long as it won't short out the 5v heater circuit. The reakly easy way would be to remove the downpipe and just tack another bung on the other side of the pipe in there, and I may do that later if and when I upgrade the turbo, since I'll have the downpipe off, but I'm lazy and just want to know if anyone wouldn't do this. Last edited by reid-o : 06-17-2006 at 11:13 AM.

07-17-2006, 07:24 AM	#30
crystal_Imprezav Spec C Club Car: Slow 05 STi Fav Mod: Loping Idle Location: Chewy's Garage Posts: 1,845 Join Date: Mar 2005 Trader Rating: (11)	BTW just as an update, I zipped tied my o2 sensor as well to the tranny brace to run my lc-1 and it did exhibit the same rich closed loop conditions you all are seeing. 13.8 while cruising at part throttle and 14.3 when at a stop for a couple of seconds until it goes back up to 14.7. Got my o2 bung welded into my DP yesterday and stuck the stocker back into its place and the wideband into its new bung and wah-lah AFR's back to 14.7 at part throttle and at a stop. FWIW I didnt get a CEL for over 2 weeks with the sensor tied up until I was about 10 miles from the shop. Just an update for the thread. This ad is not endorsed by this member. Please register or login to hide this ad.

06-15-2006, 07:00 AM	#17
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)	Cool. Well, not cool ... but cool because 3 of us have confirmed that we all experience this unusual rich phenomena and all 3 of us removed the rear O2. When I reinstalled my rear O2 sensor things went back to normal. If one of you guys could try that then that would pretty much seal the deal (as if it isn't already). t

06-15-2006, 07:13 AM	#18
daemon Professional STI Racer Car: 2004 STi Location: Florida Posts: 784 Join Date: Feb 2004 Trader Rating: (0)	Wonder if it is electrical or computational in nature. If the sensor is still plugged into the electrical connector but not installed in the pipe, would the issue still occur? Is the ECU doing some sort of difference calc on the front vs. rear reading or does it just want the circuit connected?

06-15-2006, 07:33 AM	#19
jays05 Spec C Club Fav Mod: when it's not blown up Location: Upstate NY Posts: 1,470 Join Date: Nov 2004 Trader Rating: (0)	I was also wondering if this was an electrical problem vs ecu logic. I won't have time to get under the car to hook back up the rear o2 till next weekend.

06-15-2006, 07:42 AM	#20
R4ND0M_AX3 Grassroots STI Racer Car: 05 Subaru WRX STi Fav Mod: Cobb StreetTUNER Location: Elk Grove, CA USA Posts: 590 Join Date: Jul 2004 Trader Rating: (0)	I don't yet have an extra bung for both the wideband and stocker.

06-15-2006, 07:42 AM	#21
sebtarta Spec C Club Car: Waiting for the STI Fav Mod: Driving My Car Location: I Don't Know Posts: 1,660 Join Date: Sep 2005 Trader Rating: (7)	Wolf did you try leaving the connector of the O2 connected and place the wideband where the O2 goes? Just zipt tie the O2 somewhere and go for a test, leaving the O2 connected.

06-23-2006, 12:25 PM	#27
crystal_Imprezav Spec C Club Car: Slow 05 STi Fav Mod: Loping Idle Location: Chewy's Garage Posts: 1,845 Join Date: Mar 2005 Trader Rating: (11)	Has anyone tried the PLX M-300 wideband that has the narrowband analog outputs that can trick the ecu into believeing the stock o2 is still there. I too do not have an extra o2 bung and was about to order the LC-1 until I saw this feature on the PLX. I wonder if you hook up the PLX wideband sensor and run the analog wires down to the stock o2 sensor harness and hook it up there if the car will act as normal. Anyone try this or something similar? Cobb maybe since I know you guys are using the PLX wideband?

06-23-2006, 03:58 PM	#28
R4ND0M_AX3 Grassroots STI Racer Car: 05 Subaru WRX STi Fav Mod: Cobb StreetTUNER Location: Elk Grove, CA USA Posts: 590 Join Date: Jul 2004 Trader Rating: (0)	The LC-1 (and LM-1) has the analog outputs that can be configured as a stock sensor also. There are two 0-5V analog outputs. I think the first one is already setup like a typical narrowband.

06-24-2006, 06:27 AM	#29
Merchgod Junior STI Driver Posts: 81 Join Date: Apr 2006 Trader Rating: (0)	The rear O2 sensor is used to make additional small changes to closed loop fueling. I have my rear O2 still installed in my WRX with the mechanical extender and my ECU explorer logs occasionally show it pulling less than 1 percent of fuel. Not sure if ST logs show the rear o2 correction, but ECUexplorer shows it as the parameter A/F Correction #3. I'm guessing that with Cobb's extended threshold for rear o2 failure, perhaps the ECU, which would normally throw a CEL and ignore the rear o2 if it saw no signal, is now considering the non-signal as a super lean condition post-cat and using the maximum authority allowed by a "functioning" rear o2 to richen the mixture in closed loop.