Wideband sensor location

[scottrx7tt]

I know most of you put your wideband sensors just past the turbo. I have mine in the J pipe where the factory bung is. I was wondering if it really matters? Are my o2 readings off with my sensor before the turbo?

[jsveb]

Possibly, and I would be concerned that a fragment from the O2 sensor might damage the turbo and possibly the engine following that.

[patina]

Originally Posted by jsveb

Possibly, and I would be concerned that a fragment from the O2 sensor might damage the turbo and possibly the engine following that.

well said

[Rawknees'Turbo]

I would have to do some digging to find the info, but someone in the past explained how having a wideband sensor before the turbo means that readings will be inaccurate due to the backpressure created by the turbocharger (something along those lines). I think it was JFairman that explained it.

[speednme1]

I assume you want to read your afr. Afr (air fuel ratio) would include the air that passes through the intercooler and your air intake. How can you correctly view afr's from the j-pipe. The mixture(for correct wideband readings after the turbo?) happens at the turbo. So the correct placement would be after the turbo (discharge side)....before the turbo...you will not get correct readings.....now I could be wrong as that is my theory....let the experts chime in

[scottrx7tt]

Originally Posted by speednme1

I assume you want to read your afr. Afr (air fuel ratio) would include the air that passes through the intercooler and your air intake. How can you correctly view afr's from the j-pipe. The mixture happens at the turbo. So the correct placement would be after the turbo (discharge side)....before the turbo...you will not get correct readings.....now I could be wrong as that is my theory....let the experts chime in

The air/fuel ratio is measured in the exhaust, not in the intake charge. The air and fuel mix in the intake runners before being injected into the cylinder. Most of the 930 guys usually put their sensors just past the turbo on the exhaust side. The factory narrow band sensors are in the J pipe.

[speednme1]

Originally Posted by scottrx7tt

The air/fuel ratio is measured in the exhaust, not in the intake charge. The air and fuel mix in the intake runners before being injected into the cylinder. Most of the 930 guys usually put their sensors just past the turbo on the exhaust side. The factory narrow band sensors are in the J pipe.

I thought you wanted to know wideband placement for a turbo car. My theory may not be 100% for a turbo car for wideband placement(or completely wrong for that matter) but wouldn't the exhaust gas temperatures (in the j-pipe) heat the sensor a bit too much, with the possibility of it getting destroyed thus destroying your turbo in the process....hmm I would rethink placing it before the turbo....if not for anything else than saving my turbo...then again it's your car

[bpu699]

Wouldn't the best place for a wideband be exactly where the factory mounted the O2 sensor?

I have a PLX AFR meter which I like, as it replaces the stock O2 sensor with a wideband one, and then passes this signal to the display and passes the same signal through to the car. Basically, it acts as a splitter. No need for new bungs, drilling, or guessing. What the cars computer sees, is exactly what you see...

Bo

[pkabush]

Originally Posted by Rawknees'Turbo

I would have to do some digging to find the info, but someone in the past explained how having a wideband sensor before the turbo means that readings will be inaccurate due to the backpressure created by the turbocharger (something along those lines). I think it was JFairman that explained it.

Agreed. Everything I've read on the subject says to locate it downstream from the turbo. This insures accurate readings and mitigates any possible damage to the turbo. The bungs are cheap, and if you don't weld, any exhaust shop should be able to weld it up for less than $50. Also, don't forget to mount it at a angle (about 15 degrees iirc) to prevent water damage to the sensor.

[speednme1]

Originally Posted by speednme1

I assume you want to read your afr. Afr (air fuel ratio) would include the air that passes through the intercooler and your air intake. How can you correctly view afr's from the j-pipe. The mixture(for correct wideband readings after the turbo?) happens at the turbo. So the correct placement would be after the turbo (discharge side)....before the turbo...you will not get correct readings.....now I could be wrong as that is my theory....let the experts chime in

For the experts...is the compressed air and the ambient air on the turbo taken into account when tuning if using a wideband on the discharge of the turbo? Just curios(these percocets aren't helping)

[Rawknees'Turbo]

Originally Posted by speednme1

For the experts...is the compressed air and the ambient air on the turbo taken into account when tuning if using a wideband on the discharge of the turbo? Just curios(these percocets aren't helping)

No Rey - only the exhaust gasses (the oxygen content in the exhaust gas is measured).

[speednme1]

Originally Posted by Rawknees'Turbo

No Rey - only the exhaust gasses (the oxygen content in the exhaust gas is measured).

Thank you for the response "new guy"....you're full of good info....you remind me of a guy that used to frequent these pages.....knowledgable chap...who got biatch slap out of these boards....man he was funny

[Rawknees'Turbo]

Originally Posted by speednme1

Thank you for the response "new guy"....you're full of good info....you remind me of a guy that used to frequent these pages.....knowledgable chap...who got biatch slap out of these boards....man he was funny

Ha ha - I hear he blames his friends on here for his bad behavior; some of them are terrible influences, buttofcourse!!!


Like that 70'sbush dude that posted a little above; the guy's always trying to start some **** with his "dilivar is acceptable" comments!!! Same with Kenik-da'-Freak, too!!!

[Raceboy]

There is Bosch official paper that specifies the effect of pressure on the readings, they will be off before turbo due to higher pressure. And heat will kill the sensor much sooner. Narrowband sensors are much more resistant to heat.

Regarding LSU4.2, Bosch states operating temperature to be ~930C (max short term 1030C) but in practice they die soon with high temps. LSu4.9 is much better in this regard.

[Speedy Squirrel]

The J-Pipe location is great for the stock switching-type O2 sensor. It warms up quickly there (O2 sensors need to be over 600 C to work). Since the stock system only uses the O2 sensor at idle and very low throttle, the exhaust backpressure is minimal, and the reading is not affected significantly.



For performance use, the switching type sensor is replaced by a wide range O2 sensor (WRO2). Since the desire is to monitor A/F ratio under full load conditions, the exhaust backpressure on a turbo motor will be significant. At 1 bar boost (2 bar absolute pressure), the backpressure can be between 1.8 to 2.3 bar absolute. The chart below (for the Bosch LSU WRO2) shows that this will produce errors of 15% or more in the O2 reading. Further, there is a dependency on mixture (rich or lean).



It is not uncommon for OEM's to correct for this effect using software. We do this to allow the O2 sensor to be located before the turbo, where it can warm up more quickly, which benefits emissions control, and allows a little quicker Lambda control generally.

[scottrx7tt]

Awesome info! Exactly what I was looking for. I was trying to take the easy approach using the stock location. A 15% richer reading over actual is pretty significant, especially under boost conditions.

Originally Posted by Speedy Squirrel

The J-Pipe location is great for the stock switching-type O2 sensor. It warms up quickly there (O2 sensors need to be over 600 C to work). Since the stock system only uses the O2 sensor at idle and very low throttle, the exhaust backpressure is minimal, and the reading is not affected significantly.



For performance use, the switching type sensor is replaced by a wide range O2 sensor (WRO2). Since the desire is to monitor A/F ratio under full load conditions, the exhaust backpressure on a turbo motor will be significant. At 1 bar boost (2 bar absolute pressure), the backpressure can be between 1.8 to 2.3 bar absolute. The chart below (for the Bosch LSU WRO2) shows that this will produce errors of 15% or more in the O2 reading. Further, there is a dependency on mixture (rich or lean).



It is not uncommon for OEM's to correct for this effect using software. We do this to allow the O2 sensor to be located before the turbo, where it can warm up more quickly, which benefits emissions control, and allows a little quicker Lambda control generally.

[bpu699]

Very interesting...

My car reads very rich under boost... Afr <10...

My sensor is in the stock location...

So are we saying at 0.8 bar it might be reading richer than it is?

Will move it behind the turbo if it makes a difference...

You learn something new every day...

[Speedy Squirrel]

Yes, it is reading richer than it really is, probably 10 to 15 percent.

Originally Posted by bpu699

Very interesting...

My car reads very rich under boost... Afr <10...

My sensor is in the stock location...

So are we saying at 0.8 bar it might be reading richer than it is?

Will move it behind the turbo if it makes a difference...

You learn something new every day...

[flightlead404]

Originally Posted by speednme1

I thought you wanted to know wideband placement for a turbo car. My theory may not be 100% for a turbo car for wideband placement(or completely wrong for that matter) but wouldn't the exhaust gas temperatures (in the j-pipe) heat the sensor a bit too much, with the possibility of it getting destroyed thus destroying your turbo in the process....hmm I would rethink placing it before the turbo....if not for anything else than saving my turbo...then again it's your car

wideband sensor is thermostatically controlled. can't imagine that as far away from the heads as the bung is that the temp there doesn't fall inside the region of controllability.

what makes a wideband o2 sensor more likely to fail and cause turbo damage than a factory narrow band sensor?

inaccuracy due to pressure is a whole 'nothing thing and a reasonable reason to locate aft of the turbo.

[TurboKraft]

Speedy is spot-on, great data. Post-turbocharger is the correct location.

+1 flightlead -- no reason one will degrade any more than the factory sensor.