STS & Wideband O2 Sensor Placement
Thread Starter
Staging Lane
Joined: Jan 2005
Posts: 77
Likes: 0
STS & Wideband O2 Sensor Placement I've searched and I've found that almost everybody says to put the O2 sensor after the turbo. I just want to make sure in my specific application that's still the correct spot to mount it. I still have cats on the car and behind the turbo looks like this -
- will having the exhaust split and the tip so close to the sensor affect the reading at all?
- will having the exhaust split and the tip so close to the sensor affect the reading at all?
IMO I would highly reccomend placing the O2 before the turbo because there you are reading raw gases out of the engine. If you place it after the turbo you drop the ability to properly read the gases.
For example if you place it after the turbo and you are running rich there is the possibility that the heat from the turbo could assist the gas in burning resulting in a less than accurate reading. Yes the reburned gas will still read on the O2 but not as accurately. From what I have seen over the years.
Although I have seen set ups with the O2's mounted after the turbo and they seem to run ok but I'm not for sure how well.
Also with it mounted that close to the exit/tips for the exhaust you will have inaccurate readings thus the reason to mount it further up the line.
For example if you place it after the turbo and you are running rich there is the possibility that the heat from the turbo could assist the gas in burning resulting in a less than accurate reading. Yes the reburned gas will still read on the O2 but not as accurately. From what I have seen over the years.
Although I have seen set ups with the O2's mounted after the turbo and they seem to run ok but I'm not for sure how well.
Also with it mounted that close to the exit/tips for the exhaust you will have inaccurate readings thus the reason to mount it further up the line.
Joined: Jun 2004
Posts: 1,501
Likes: 7
From: Ft. Irwin, California (But Virginia is home)
I have mine in the passanger side header collector (before the cat). Ran LT's + cats on my STS (hien it was installed). Gave accurate readings. Putting the sensor way back there will scew the readings (like OreoLT1 said). The cats will affect the reading too.....which is why you want the sensor before the converters.
Put it after the turbo on the exhaust pipe above the 3 or 9 o'clock position! Running the sensor on the pressure side is a no-no, as the sensor will not read correctly and the high exhaust pressures and temperatures will eventually damage the sensor.
As SSnakekiller said, after the turbo b/c of the backpressure. The only downside is that the cats can throw off the reading also. I would suggest right after the turbo and remove the cats. The cats will can deteriorate with high EGTs on the pressure side and eventually could cause turbo problems.
"TurboLT1" and "SSnakekiller" I'm just curious for my own knowledge what type of pressures are you seeing(?) in the exhaust to damage an O2 snsr as far as backpressure reading,boost level, etc? I haven't seen it before and I'm curious to see under what circumstances. Once again not saying that it couldn't happen.
I have run with wideband's in the post O2's location with no cats on numerous FI cars both turbo and SC for a few years now and no trouble has come about. But if you guys have run them post turbo and still have good readings well their's another shrimp on the barbie!
I second the elimination of the cats. on a rear mount turbo at all costs, unless your good with rolling the dice or have plenty of time and money for rebuilds!
I have run with wideband's in the post O2's location with no cats on numerous FI cars both turbo and SC for a few years now and no trouble has come about. But if you guys have run them post turbo and still have good readings well their's another shrimp on the barbie!
I second the elimination of the cats. on a rear mount turbo at all costs, unless your good with rolling the dice or have plenty of time and money for rebuilds!
Joined: Jun 2004
Posts: 1,501
Likes: 7
From: Ft. Irwin, California (But Virginia is home)
"TurboLT1" and "SSnakekiller" I'm just curious for my own knowledge what type of pressures are you seeing(?) in the exhaust to damage an O2 snsr as far as backpressure reading,boost level, etc? I haven't seen it before and I'm curious to see under what circumstances. Once again not saying that it couldn't happen.
I have run with wideband's in the post O2's location with no cats on numerous FI cars both turbo and SC for a few years now and no trouble has come about. But if you guys have run them post turbo and still have good readings well their's another shrimp on the barbie!
I second the elimination of the cats. on a rear mount turbo at all costs, unless your good with rolling the dice or have plenty of time and money for rebuilds!
I have run with wideband's in the post O2's location with no cats on numerous FI cars both turbo and SC for a few years now and no trouble has come about. But if you guys have run them post turbo and still have good readings well their's another shrimp on the barbie!
I second the elimination of the cats. on a rear mount turbo at all costs, unless your good with rolling the dice or have plenty of time and money for rebuilds!
x2 Trending Topics
I have moved from semi-conductors to motorsports somewhat recently. I can't make mention since we are not a sponsor, but wideband technology is really a large part of it's core. We work with everything from the cheap Bosch LSU's that were OEM equipment to some very high-end sensors used in labs, aerospace, and OEM calibration. The common Bosch sensor that is used in most of the consumer grade widebands (the 250-450 dollar range) is very sensitive to pressure and the controllers have no way to compensate for it. They do need to be after the turbo. I have some pressure data at work but most of it is held pretty tightly.
Last edited by Frost; Jun 30, 2008 at 11:08 PM.
LS1 Tech Stories
The Best V8 Stories One Small Block at Time
6 Common C5 Corvette Failures and What's Involved In Repairing Them
Pouria Savadkouei
Retro Modern Bandit Pontiac Trans AM Comes With Burt Reynolds' Autograph
Verdad Gallardo
Top 10 Greatest Cadillac V Series Performance Models Ever, Ranked
Pouria Savadkouei
Top 10 Most Powerful Chevy Trucks Ever Made!
Hennessey's New Supercharged Silverado ZR2 Has 700 HP
Verdad Gallardo
Coachbuilt N2A Anteros Is an LS2-Powered C6 Corvette In Italian Clothes
Verdad Gallardo
Awesome K5 Blazer Restomod Comes With C7 Corvette Power
Verdad Gallardo
10 Camaros You Should Never Buy
10 LS Engine Myths That Refuse to Die
Verdad Gallardo Joined: Jun 2004
Posts: 1,501
Likes: 7
From: Ft. Irwin, California (But Virginia is home)
I have moved from semi-conductors to motorsports somewhat recently. I can't make mention since we are not a sponsor, but wideband technology is really it's core. We work with everything from the cheap Bosch LSU's that were OEM equipment to some very high-end sensors used in labs, aerospace, and OEM calibration. The common Bosch sensor that is used in most of the consumer grade widebands (the 250-450 dollar range) is very sensitive to pressure and the controllers have no way to compensate for it. They do need to be after the turbo. I have some pressure data at work but most of it is held pretty tightly.
Fair enough explanation, but wouldn't the effect of the cats skew the WBO2 reading? I ran my STS for 2 1/2 years and 15K miles w/ the WB in the passangr collector. The car should have eaten the engine if it was off too much, shouldn't it?I can see on a front mount putting it in the downpipe, but the rear mount has it's own strange quirks........ not saying I'm 100% right.......
In the downpipe is common fare for a front mount as well. The cats will skew a wideband; the OEM ones worse than higher flowing replacements. At WOT, the replacements are actually doing very little to the gas moving through them but the factory cats will still cause some error. This error is more pronounced on NA applications than FI in general as well, just as logic would dictate from the higher level of gases moving through. The amount of error presented is also relevant to the application though, and the error introduced at WOT in almost any case shouldn't be detrimental unless you are really running on the ragged edge. Most people tune to the tenth in AFR, and most people would be a little dismayed when seeing a higher end wideband running against a Bosch LSU based system. Two to three tenths in AFR error is pretty common, especially on the LSU based controllers that are reliant on the cal resistor over free-air calibration, and those type only drift further out over time.
Joined: Jun 2004
Posts: 1,501
Likes: 7
From: Ft. Irwin, California (But Virginia is home)
In the downpipe is common fare for a front mount as well. The cats will skew a wideband; the OEM ones worse than higher flowing replacements. At WOT, the replacements are actually doing very little to the gas moving through them but the factory cats will still cause some error. This error is more pronounced on NA applications than FI in general as well, just as logic would dictate from the higher level of gases moving through. The amount of error presented is also relevant to the application though, and the error introduced at WOT in almost any case shouldn't be detrimental unless you are really running on the ragged edge. Most people tune to the tenth in AFR, and most people would be a little dismayed when seeing a higher end wideband running against a Bosch LSU based system. Two to three tenths in AFR error is pretty common, especially on the LSU based controllers that are reliant on the cal resistor over free-air calibration, and those type only drift further out over time.
I need to really pry my butt out of Williamsburg some day and go to one of the RPM get-togethers. Always like talking tuning and theory w/ people that understand it better than I do..... like my friend Brian (does work for Va Speed). 
Last edited by Schantin; Jun 30, 2008 at 11:43 PM.
Taken straight from the innovate manual:
This is of course referring to front mount turbo's, but the same rule applies about pressure.
On TURBO CHARGED vehicles:
Bung: Install the bung downstream from the turbo before the catalytic
converter. The high exhaust pressure before the turbo interferes with
the lambda measurement and the high exhaust temperatures
encountered there can damage the sensor.
Bung: Install the bung downstream from the turbo before the catalytic
converter. The high exhaust pressure before the turbo interferes with
the lambda measurement and the high exhaust temperatures
encountered there can damage the sensor.
This is of course referring to front mount turbo's, but the same rule applies about pressure.
W2W installed their wideband about 6" behind the passenger collector, they told me theres to much of a difference from there to the downpipe and recommended me to keep it there. I always thought to do it in the DP too but im gonna take their advice.
Thread Starter
Staging Lane
Joined: Jan 2005
Posts: 77
Likes: 0
Some of you have it before the cats and before the turbo and its perfectly fine. Some of you have it after the turbo and after the cats and its perfectly fine. Each tuner has a different spot they like to install it. It seems like either way there's going to be drawbacks because of the nature of an STS.
One of my main concerns hasn't really been addressed though, is that location to close to the exhaust tip to get an accurate reading? Will it mix with air moving back into the exhaust and skew the reading?
One of my main concerns hasn't really been addressed though, is that location to close to the exhaust tip to get an accurate reading? Will it mix with air moving back into the exhaust and skew the reading?
I have also been running AEM wideband in the stock after cat bung (no cats) for a few years now on my daily driver STS with no issues that I can tell. seems pretty darn accurate. PS: I am running 12PSI. some more food for thought is the car is tuned off and reacts to the pre cat O2 sensors. the pressure squing them would/should be an issue to you would think.
~Guy
~Guy
Just owner pref. I guess. 