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Old 01-27-2010, 10:54 PM   #1
arghx7
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Default Stop calling the stock front O2 sensor a narrowband...

... because it's not, whether you trust its readings or you don't.

The front sensor is a wideband and the rear is a narrowband just like many other modern cars. It's clearly stated in the service manual (using 04 Impreza/WRX/STi manual here). The service manual contains the AFR vs voltage curve and the ECU itself contains the AFR vs current curve. We can compare these curves with those of other wideband manufacturers and it becomes clear that the front O2 sensor is really no different.



That's your factory front O2 AFR vs voltage curve--completely unlike a narrowband O2, which I will demonstrate.



That's the factory AFR vs voltage curve from an OEM Toyota wideband. It's not so different from the Subaru ones as you can see.



That's the calibration of a stock front O2 sensor showing amperage on the X axis and AFR on the Y axis taken right from ECUflash.



And that's the calibration of the Bosch LSU sensor (OEM wideband on VW Beetle turbo and other cars). This is the same/similar sensor to what is used in the Innovate LC-1, AEM UEGO, etc. Granted, here it is expressed in lambda and the axes are flipped. But it again shows the similarity between the Bosch sensor and the factory front O2 sensor.

Your OEM narrowband is behind the cat:



It is mostly used to measure catalyst efficiency. The output voltage is a step function that switches right at lambda = 1 or 14.7:1 on a normal engine.


As you can see there is no major difference between the factory front O2 sensor and your typical aftermarket wideband incorporating the Bosch LSU sensor, except maybe the location in which it is installed. Yes the exhaust pressure under boost does have some effect on the reading. And I know I'm going to get hammered for this comment, but wideband readings always vary with location anyway so one reading isn't guaranteed to be "right" over another

There are still reasons to run an aftermarket wideband (I own one). You may or may not trust its accuracy under boost, but to say that the factory front O2 sensor is a narrowband sensor is simply not true.
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Old 01-28-2010, 12:21 AM   #2
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the signal used by the ecu is narrow
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Old 01-28-2010, 12:30 AM   #3
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did you read and comprehend what I posted?
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Old 01-28-2010, 12:39 AM   #4
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yes the factory front o2 sensor is a wideband.

no it is not usable for tuning purposes. Mine registers 13:1 or higher during pulls and this is just simply incorrect. extraordinarily high EGBP (40-60+ psi) really messes with this sensor when the car is under boost.

i now fail to understand the point of this thread, other than to educate people that the front o2 is a wideband.
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Old 01-28-2010, 12:48 AM   #5
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No matter what the specs say... in practice, the front O2 is narrowband.

It doesn't matter what O2 sensor you put before the turbo, once you go under boost and put 30+ psi of backpressure into the header / uppipe, it becomes useless, because it's not calibrated at those pressures. Any wideband O2 used in that location will become narrow in practice due to the pre-turbo back pressure... and back pressure happens there precisely when you need it to work as a wideband.

If you want to use that sensor as an actual wideband, you need to convert your car to N/A. Then it will work as a wideband. Have fun with that.
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Old 01-28-2010, 09:40 AM   #6
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Quote:
Originally Posted by Uncle Scotty View Post
the signal used by the ecu is narrow
Quote:
Originally Posted by arch4life View Post
yes the factory front o2 sensor is a wideband.

no it is not usable for tuning purposes. Mine registers 13:1 or higher during pulls and this is just simply incorrect. extraordinarily high EGBP (40-60+ psi) really messes with this sensor when the car is under boost.

i now fail to understand the point of this thread, other than to educate people that the front o2 is a wideband.
Quote:
Originally Posted by Concillian View Post
No matter what the specs say... in practice, the front O2 is narrowband.

It doesn't matter what O2 sensor you put before the turbo, once you go under boost and put 30+ psi of backpressure into the header / uppipe, it becomes useless, because it's not calibrated at those pressures. Any wideband O2 used in that location will become narrow in practice due to the pre-turbo back pressure... and back pressure happens there precisely when you need it to work as a wideband.

If you want to use that sensor as an actual wideband, you need to convert your car to N/A. Then it will work as a wideband. Have fun with that.
oooooh


00000000h

these d0000ds might just be on to something, here
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Old 01-28-2010, 09:52 AM   #7
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IME, the factory front oxygen sensor works pretty well as a wideband when you put it after the turbo.....I did some back to back testing with the stock VS my LC1 and the response of each was a similar function, as shown in those graphs above.

The stock sensor bottoming out at 11:1 is a limiting factor, but its not as useless as everyone makes it seems, when it is moved to a more logical position.

M@
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Old 01-28-2010, 10:56 AM   #8
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Okay, from now on you must call it a

"morethannecessaryfortheECUduringclosedloopbutnotq uiteenoughnecessaryfortuningopenloopband"

Cause that is much easier.
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Old 01-28-2010, 11:04 AM   #9
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Quote:
Originally Posted by Agkelos View Post
Okay, from now on you must call it a

"morethannecessaryfortheECUduringclosedloopbutnotq uiteenoughnecessaryfortuningopenloopband" sensor

Cause that is much easier.
i like this d000000000000000000000d
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Old 01-28-2010, 11:10 AM   #10
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Cool story bro.
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Old 01-28-2010, 12:27 PM   #11
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I've tuned using the stock front O2 sensor in the stock location [gasp]. Yeah the exhaust pressure throws it off a little, but it's not that big of a deal. O2 sensors are like dynos and knock sensors... they all vary and you can't tune a car based on only one of those alone. Unless you have a real 5 gas analyzer (reads HC, CO, NOx, O2, CO2) you're going to be limited by the equipment.

Quote:
Originally Posted by mattminer
The stock sensor bottoming out at 11:1 is a limiting factor, but its not as useless as everyone makes it seems, when it is moved to a more logical position.
The 11:1 signal clamp isn't as big of a deal as people make it out to be. Widebands aren't very accurate when you get that far from stoich, which is probably why the factory engineers clamped the stock sensor's signal there. Now I know that vendors will try to sell you on their product's accuracy (I've had multiple aftermarket widebands) but they are all using off-the-shelf sensors designed for another car anyway. Specifically they are mostly using the Bosch LSU 4.2 from late 90s VW/Porsche/Audi or the NTK/NGK sensor used in an obscure trim package of Honda Civic for a couple years.
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Old 01-29-2010, 12:33 AM   #12
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it seems like everyone just likes to jump on the wagon and bash the factory front sensor, even though its essentially the same thing as the bosch unit, and works fine after its moved.

I wasnt saying that the 11:1 limit was a huge deal, just pointing it out as pretty much the only limitation.
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Old 01-29-2010, 12:43 AM   #13
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Quote:
Originally Posted by mattminer View Post
it seems like everyone just likes to jump on the wagon and bash the factory front sensor, even though its essentially the same thing as the bosch unit, and works fine after its moved.

I wasnt saying that the 11:1 limit was a huge deal, just pointing it out as pretty much the only limitation.

until the OP realizes this, he's going to be tuning cars ULTRA rich if he's trying to hit 11:1 on that sensor during a pull.

for what its worth, there has been some discussion in the open source community regarding rescaling the non-narrowband areas of the front o2 sensor to mimic the readouts of a wideband post turbo. I'd look into that before you tune more cars wayy to rich.
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Old 01-29-2010, 12:28 PM   #14
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Quote:
Originally Posted by Concillian View Post
If you want to use that sensor as an actual wideband, you need to convert your car to N/A. Then it will work as a wideband. Have fun with that.
Or you can just move the sensor to the downpipe...
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Old 01-29-2010, 01:13 PM   #15
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I compared the stock sensor to a wideband 5 years ago.

http://www.iwsti.com/forums/cobb-str...lots-data.html

t
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Old 01-29-2010, 01:13 PM   #16
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I compared the stock sensor to a wideband 5 years ago.

http://www.iwsti.com/forums/cobb-str...lots-data.html

t
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Old 01-30-2010, 04:42 AM   #17
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Not to bring us off course here. But i've had a question for awhile and it seems like this post, kinda goes with it, where should i put my aem wideband, it says 36" away from the turbo. But the bung on my invidia downpipe is pretty much right off the bellmouth. Im sure i wouldnt get a good reading there. Or am i just mistaken.?
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Old 01-30-2010, 10:38 AM   #18
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Hey the v8 STi has the wideband stock O2 sensor after turbo in the D/P. Think about them apples.

Yes it is a waste to put such an expensive sensor pre-turbo. But hey, maybe it idles better using a better sensor???
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Old 01-30-2010, 12:05 PM   #19
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Quote:
Originally Posted by WolfPlayer View Post
I compared the stock sensor to a wideband 5 years ago.

http://www.iwsti.com/forums/cobb-str...lots-data.html

t
Yes I've seen this. The problem with your tests is that you are comparing two of the same instruments which are subject to the same limitations. You've got two widebands which, despite what internet forums say, are inherently limited in their accuracy when you aren't near lambda=1. They are way better than narrowband sensors but they are still limited by the nature of the pump cell/nernst cell design. A better test would have been to compare the factory wideband, the Bosch wideband, and readings from an actual 5 gas analyzer (which are expensive, the Snap-On one is about $3000).

With a wideband O2, You've got higher exhaust pressure before the turbo (which can increase pump cell current and result in a richer reading). But then there's lower temperature/greater distance after the turbo, which results in less pump cell current and a leaner reading.

So which one is right? How do you reconcile all the recommendations to

1. minimize exhaust pressure
2. get the sensor as close to the exhaust port as possible without damaging it
3. keep the exhaust temperature close to the operating temperature of the sensor (about 1300F)

Well, you don't--not completely, not with a wideband sensor. Consumer grade wideband O2 sensors are not designed to do what we do with them really. Under heavy load they are imprecise at best. They were designed for greater accuracy around the stoichiometric AFR range, relative to the older narrowband sensors. And they accomplish that very well. But they are NOT 5 gas analyzers.



5 gas analyzers compare the exhaust to a controlled sample of reference gas. They don't rely on pump cells and nernst cells and all the constraints associated with them. So far all we know from your test is 1) exhaust backpressure affects readings and 2) under heavy load, the farther the sensor is from the engine the leaner it reads (which is true on non turbo cars as well). There's nothing new there.

That's why you always have to be careful with how much trust you place in widebands, or knock sensors, or your typical chassis dyno.
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Old 01-30-2010, 12:14 PM   #20
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Quote:
Originally Posted by arghx7 View Post
That's why you always have to be careful with how much trust you place in widebands, or knock sensors, or your typical chassis dyno.
My wideband works great.
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Old 01-30-2010, 12:19 PM   #21
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I don't doubt that it works, I am just pointing out that there are inherent limitations in ALL widebands. If two sensors are functioning properly and are in different locations you can't have one 100% "correct" and one 100% "wrong" wideband, not under such rich mixtures. That doesn't mean they are useless instruments (I've owned two different aftermarket ones and of course I've used the OEM Subaru), it just means that they are somewhat blunt instruments.

This is a more complex way of looking at it than what various wideband manufacturers pushing products will tell you.
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Old 02-06-2010, 03:47 PM   #22
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Quote:
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Yes I've seen this. The problem with your tests is that you are comparing two of the same instruments which are subject to the same limitations.
Actually - no. I disagree. My test was to simply show that the stock sensor is not accurate in terms of real world AFR numbers. Fact is - when you get away from stoichiometric, the stock sensor (wideband or not), is not accurate while using the factory calibration table in the ECU. Why? because the darn thing is in the pre-turbo exhaust where the pressure is often very high.

I actually recalibrated the stock sensor in the ECU and have had very good results from doing that.

If you utilize the stock sensor and expect accurate AFR readings when you are on boost (i.e. there is high pre-turbo exhaust pressure), you are playing with fire. The readings in this situation are absolutely inaccurate. This has been known AND CONFIRMED by many people through the years.

Yes, I found out a couple YEARS ago that the factory sensor is actually a quasi-wideband. I say quasi because it isn't the best correlation in terms of mV to lambda. That said - it still makes no difference. The setting in the ECU are incorrect because there is no adjustment for pressure and - as I am sure you know - pressure seriously throws off O2 readings (wideband or not). The stock factory sensor would work great in terms of accuracy (i.e. wideband accuracy) if only Subaru would have put it AFTER the turbo where there is little pressure.

One of the best changes you can make is to pull the stock O2 sensor out of the exhaust manifold and move it to the downpipe (where so many aftermarket companies have a bung). The sensor wiring is long enough to take it there. Works great there too.

t
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Old 02-06-2010, 04:37 PM   #23
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Quote:
My test was to simply show that the stock sensor is not accurate in terms of real world AFR numbers.
I see you didn't read my post. Your definition of real world AFR is whatever is measured by a Bosch sensor located behind the turbo. Temperature and pressure still affect the signal when the sensor is located behind the turbo. It is an inherent problem in all widebands. The sensor still isn't at reference conditions. I can put two sensors right next to either and they will agree with each other, but that doesn't mean they are "right."

Only a five gas analyzer can tell you the "real" AFR because it measures the AFR in a completely different way.
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Old 02-06-2010, 05:28 PM   #24
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Quote:
Originally Posted by arghx7 View Post
I see you didn't read my post. Your definition of real world AFR is whatever is measured by a Bosch sensor located behind the turbo....
I don't think we're communicating properly. Let me state what I clearly mean.

There are thousands of custom tunes done on Subaru WRXs and STIs. 99.9% of these were done while also watching a POST turbo wideband ... bosch, NTK, whatever. When tuning our cars using a post turbo wideband as a tool, we like to shoot for anywhere between 10.8:1 to 11.8:1 on high test pump fuel. Simple as that. If you start talking about how our cars have a wideband that we can use for tuning, then you are going to cause people who are tuning their own cars to blow up their motor. Simple as that. The stock front O2 sensor will most often read really rich while another 'wideband' placed after the turbo will read leaner (when looking around 11:1). We know that we can tune these cars with an after-Turbo wideband for ~11:1. Won't be long before someone tries to use the stock O2 for tuning purposes because you said they could. However, when they think they are running 11:1 they will actually be running 12:1 or leaner.

t
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Old 02-06-2010, 06:15 PM   #25
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I tuned a v8 twinscroll that had the stock 02 post turbo. It was a few years ago, so it would be interesting to compare my logs of my WB vs the stock one.
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