Oxygen sensor in downpipe. Any advantages?

[turbo2nr]

I'm sure your fingers are tired, but what does the extra pressure exactly do to a WB before the turbo. Does it make it read leaner, richer, slower? You have not said anything, other than it is different, so what is different? Too much pressure? So what does that do?

 

[turbo2nr]

I've done this, and I've done that. You can do this, or that. I will throw out some old sayings, and then talk a little more. When I'm done, I will stop talking.

Bruce

 

[turbo2nr]

Ok, sorry for that. I have reread your posts many times. I do not see any info I can use. Other than something is different. All that typing and reading, I still have not learned anything.
Bruce, can you help me to see the light? I was thinking of getting a chip that uses a WB for WOT fuel correction. Do you have any comments on the subject? I want to get a good reading on the WB, and i have seen a WB that can send out a NB signal. Will this setup work? One sensor going to the ECM in a NB signal for idle, part throttle, then a WB signal from the same sensor going to ECM thru the old IAT sensor input wires, used for WOT fuel correction with a new stlye chip?

Thanks!

Do you know what I'm talking about?

 

[Darth Fiero]

I don't think that putting the O2 sensor AFTER the turbo is going to affect readings. The reason why I say that is the O2 sensor measures the difference between the oxygen content of the exhaust gases and the oxygen content of the ambient air. I just don't see how the readings can be any different between O2 sensor placement before or after the turbo unless you have a leak in the turbo. What is happening inside the turbo that changes the oxygen content of the exhaust? Nothing, maybe a little heat loss but that does not have any effect on oxygen content.

I believe the reason why GM put the O2 sensor before the turbo in the GN was to bring the system into closed loop faster, because obviously it is hotter there. Correct me if I am wrong but don't the Syclone/Typhoon 4.3 Turbo's come stock with the O2 in the downpipe? On my 3800 Series II turbo I am running a heated O2 in the downpipe and don't have any problems whatsoever. I could be wrong on this whole thing concerning the readings but again I just don't see how anything besides exhaust temperature changes from before to after the turbo.

 

[ijames]

The main problem with putting a wbo2 (specifically the ntk and bosch sensors) before the turbo is that they can't take the heat. At best they read wrong til they cool back off, at worst they are permanently damaged. Most controllers don't report an error when they overheat. Innovate Technologies has lots of info on this on their website in their support forums, and their lm1 does tell when the sensor overheats. See http://www.innovatemotorsports.com/forums/index.php for lots of good info, no matter what brand you wind up with.

 

[V6UnderPressure]

Ok, ALL of you have GREAT info and I appreciate all of your guys feedback! However, I would like to rephrase my question to make it a one word answer yes or no. Will it HURT the performance if I place it after the turbo? A simple yes or no question. opinions are GREAT!, however, I would like someone to tell me 1. if they had problems, or 2. they had no problems.

Scott

 

[mec108]

Originally posted by Scott4DMny
Ok, ALL of you have GREAT info and I appreciate all of your guys feedback! However, I would like to rephrase my question to make it a one word answer yes or no. Will it HURT the performance if I place it after the turbo? A simple yes or no question. opinions are GREAT!, however, I would like someone to tell me 1. if they had problems, or 2. they had no problems.

Scott

I would like to know also.

 

[mec108]

Originally posted by Scott4DMny
Ok, ALL of you have GREAT info and I appreciate all of your guys feedback! However, I would like to rephrase my question to make it a one word answer yes or no. Will it HURT the performance if I place it after the turbo? A simple yes or no question. opinions are GREAT!, however, I would like someone to tell me 1. if they had problems, or 2. they had no problems.

Scott

"ANYBODY"

 

[klatinn]

Hi,

It's all really simple. A Narrowband sensor does not care about heat or back-pressure very much. It just needs to be at it's minimum temp (~300 C) to operate. It switches at 14.7 AFR between a low voltage (lean) and high voltage (rich). That's all it does. If people post that they have different readings on an NB sensor before and after turbo, it's because they use the NB sensor for what it can't do, namely measure AFR outside it's 14.7 +- ~0.3 AFR range. It's output voltage on the rich side just varies mainly with EGT (and just a little with AFR), that's all.
A wideband sensor IS sensitive to back pressure. Some more, some less. With back pressure a WB reads richer than reality on the rich side of stoich, leaner than reality on the lean side. The NTK sensor is actually much more sensitive in that respect than the Bosch. The NTK sensor on the other hand is less sensitive to heat, and could theoretically take the pre-turbo heat. But the ECU needs to compensate for the wrong reading due to back pressure. OEM's do that by finding the appropriate compensation factors based on engine state.
The gist of it is that you can mount a Narrowband sensor before the turbo, because it can take the heat and is ignored at WOT anyway. But even a heated NBO2 does not have a heater strong enough without help from EGT's to keep at it's operating temp in all conditions.
Mount a WB sensor downstream, for accurate measurement and sensor life. In the location designed for a NBO2 you will typically be asking for trouble.

Regards

 

[V6UnderPressure]

Originally posted by klatinn

The gist of it is that you can mount a Narrowband sensor before the turbo, because it can take the heat and is ignored at WOT anyway.
Regards

Ok, again, good info, BUT can you mount a narrowband AFTER the turbo without any problems?

Scott

 

[azgn]

the problem you would have is keeping it hot enough to work.....if you used a heated 02, maybe you can get away with it

I cannot imagine any advantage to mounting a NB 02 any place but the stock location

 

[turbo2nr]

Yeah, why do you want to do that? Maybe because of the restriction in the smaller dia. header? The down pipe is a lot larger, and restriction may be less with the 02 in the DP, right?

 

[bruce]

Originally posted by Scott4DMny
Ok, again, good info, BUT can you mount a narrowband AFTER the turbo without any problems?

I've been running a heated NB where the cat. converter would be, for about 30,000 miles.

 

[bruce]

Originally posted by klatinn

A wideband sensor IS sensitive to back pressure. Some more, some less. With back pressure a WB reads richer than reality on the rich side of stoich, leaner than reality on the lean side. The NTK sensor is actually much more sensitive in that respect than the Bosch. The NTK sensor on the other hand is less sensitive to heat, and could theoretically take the pre-turbo heat.

The gist of it is that you can mount a Narrowband sensor before the turbo, because it can take the heat and is ignored at WOT anyway. But even a heated NBO2 does not have a heater strong enough without help from EGT's to keep at it's operating temp in all conditions.

Mount a WB sensor downstream, for accurate measurement and sensor life. In the location designed for a NBO2 you will typically be asking for trouble.

The Bosch is more prone to error from EGT, the LM1 even sells heat sinks to reduce this problem.

All conditons covers an insane amount of ground. Typically a heated one will work in most normal applications.

There's other issues, but yes, the WB will live longer further downstream. (talking about he TR location)

 

[2QUIK6]

I just went thru this last week. I have tried both the single wire AC Delco stocker and the NTK heated O2 sensor in both the stock location and in the DP about a ft down from the turbo.
The stock single wire will NOT work in the DP, it throws an O2 code unless you start up and immediately take off driving to get it heated up quick enough, if you start it up cold and idle for a minute or 2, it throws the code.
The heated O2, tried 2 different heated sensors, both are real lazy on the x-cnts in the DP...they are a little better in the stock location, but still not as active as the AC Delco single wire non-heated.
Yes, the O2 reading will be different in each location, I found about a 60-70mV difference between the DP and the stock location using the heated 4-wire sensor....why the difference, don't know if was the pressure or the temp...the DP read richer.

As far as at cruise and idle when in closed loop and BLM learn enabled..no difference in BLM numbers in either location..I guess when it is cyclings up and down averaging it all comes out in the wash.....the differences noted above were at WOT.
The temp does effect the readings....ever notice as EGTs climb the O2 readings will decline and its not always from becoming lean...but again knowing the reading on your car where ever the O2 sensor is when its making the most power is the only way to know if the reading is right or wrong..just takes experimentation.

So to answer your question NO, the stocker will not work in the DP very well.....a heated one does not care, you will just need to figure out at what O2 mv your car runs best at because it won't be the 770-790mV range anymore.

 

[V6UnderPressure]

Originally posted by 2QUIK6
I just went thru this last week. I have tried both the single wire AC Delco stocker and the NTK heated O2 sensor in both the stock location and in the DP about a ft down from the turbo.
The stock single wire will NOT work in the DP, it throws an O2 code unless you start up and immediately take off driving to get it heated up quick enough, if you start it up cold and idle for a minute or 2, it throws the code.
The heated O2, tried 2 different heated sensors, both are real lazy on the x-cnts in the DP...they are a little better in the stock location, but still not as active as the AC Delco single wire non-heated.
Yes, the O2 reading will be different in each location, I found about a 60-70mV difference between the DP and the stock location using the heated 4-wire sensor....why the difference, don't know if was the pressure or the temp...the DP read richer.

As far as at cruise and idle when in closed loop and BLM learn enabled..no difference in BLM numbers in either location..I guess when it is cyclings up and down averaging it all comes out in the wash.....the differences noted above were at WOT.
The temp does effect the readings....ever notice as EGTs climb the O2 readings will decline and its not always from becoming lean...but again knowing the reading on your car where ever the O2 sensor is when its making the most power is the only way to know if the reading is right or wrong..just takes experimentation.

So to answer your question NO, the stocker will not work in the DP very well.....a heated one does not care, you will just need to figure out at what O2 mv your car runs best at because it won't be the 770-790mV range anymore.

phew thanks!

 

[mec108]

Yeah "THANKS".... Rob

 

[V6UnderPressure]

For the record, the original reason I wanted to do this is because I have an EGT gauge going in. I was going to buy the adapter for the original 02 hole to accomodate the egt sensor and move the 02 sensor to the DP because I plan on going to a Wideband maybe at the end of this year. (I have an innovate WB02 kit) but I mean a full wide band system (Big stuff, fast, accel etc.). This way, I would have the fitting ready. Just trying out some info. Thanks Bruce, Rob, and any of you who put in your helpful feedback! This site rocks!

Scott

 

[2QUIK6]

That was my same plan also to put an EGT in the stock O2 loc, and you still can if you switched to the heated O2 in the DP, because if you have the EGT then WOT tuning should be done with those readings for the most part. You just have to get used to the O2 reading being a bit more in the DP and just tune to that with that in mind. As mentioned before, the idle and cruise BLMs did not seem to be effected by moving the O2 to the DP, only the WOT steady reading.

 

[bruce]

Just to tie up a few loose ends.
The highest reading will be lower (DP, NB), since the turbo acts to homogenize the exhaust pulses. There are rich and lean spots, in the exhaust flow.

This also accounts for the lower CrossCounts, but actual count can be misleading. The ecm only samples the O2, at certain intervals, to update the BL/Int. So as long as it's going rich to lean, you'll probably be fine for when it's in use.

The WBs (typically)on the other hand look, for an average low voltage, to determine richness.
So with the NB they use sampling times, and delays for when to look at that O2 to figure/refigure the BL/Int numbers.

In the world of the oems, start-up routines, and getting into closed loop quick, outweight just about everthing, other then keeping the car drivible. For the 15 seconds difference in a heated NB to come up to temp., post turbo for the average driver isn't an issue for GM they'll pay big bucks for what seems insignifigant gains.