WBO2 sensor [for AFR gauge]: where to put it with the stock mid-pipe?
10-08-2009, 02:41 PM
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WBO2 sensor [for AFR gauge]: where to put it with the stock mid-pipe?
(thread moved to a more appropriate forum)
I'm installing an AFR gauge and I am running into a problem finding a spot to put the sensor.
Following the instructions from Prosport, the location is supposed to be 18" from the exhaust port or 36" if turbo/high EGT.
Following most advice I read on O2 sensors, they need to be before the cat to be accurate.
However -- the stock setup has 13" from the exhaust port to the cat. I know one solution is get a midpipe but I am trying to put this on the stock pipe for now. This raises 2 questions/comments:
- If I put it at ~10", the sensor will likely burn out... at the very least it'll have a shortened life span. That said, the stock WBO2 is on the header at about 8"... however I can't say if the bosch 4.9 sensor is as durable. I don't want to replace the sensor every month.
- If I put it after the cat [which is what Prosport recommended to me], it is unlikely to be accurate considering how a cat works:
Blue = Oxygen
Red = Hydrocarbons (fuel)
From Wikipedia - Yes I know Wikipedia is not the end-all source for information which is why I am asking for advice here..
If the above is correct, the cat significantly alters the amount of oxygen in the exhaust gasses and pretty much eliminates any leftover fuel. How would it then be possible to accurately measure AFR after the cat?
Several other sites suggest that the reading after cat will be 0.5 leaner than what it actually is consistently, while others say that it will be completely off.
Suggestions/thoughts?
I'm installing an AFR gauge and I am running into a problem finding a spot to put the sensor.
Following the instructions from Prosport, the location is supposed to be 18" from the exhaust port or 36" if turbo/high EGT.
Following most advice I read on O2 sensors, they need to be before the cat to be accurate.
However -- the stock setup has 13" from the exhaust port to the cat. I know one solution is get a midpipe but I am trying to put this on the stock pipe for now. This raises 2 questions/comments:
- If I put it at ~10", the sensor will likely burn out... at the very least it'll have a shortened life span. That said, the stock WBO2 is on the header at about 8"... however I can't say if the bosch 4.9 sensor is as durable. I don't want to replace the sensor every month.
- If I put it after the cat [which is what Prosport recommended to me], it is unlikely to be accurate considering how a cat works:
Blue = Oxygen
Red = Hydrocarbons (fuel)
Since 1981, three-way catalytic converters have been used in vehicle emission control systems in North America and many other countries on roadgoing vehicles. A three-way catalytic converter has three simultaneous tasks:
1. Reduction of nitrogen oxides to nitrogen and oxygen: 2NOx → xO2 + N2
2. Oxidation of carbon monoxide to carbon dioxide: 2CO + O2 → 2CO2
3. Oxidation of unburnt hydrocarbons (HC) to carbon dioxide and water: CxH2x+2 + 2xO2 → xCO2 + 2xH2O
1. Reduction of nitrogen oxides to nitrogen and oxygen: 2NOx → xO2 + N2
2. Oxidation of carbon monoxide to carbon dioxide: 2CO + O2 → 2CO2
3. Oxidation of unburnt hydrocarbons (HC) to carbon dioxide and water: CxH2x+2 + 2xO2 → xCO2 + 2xH2O
If the above is correct, the cat significantly alters the amount of oxygen in the exhaust gasses and pretty much eliminates any leftover fuel. How would it then be possible to accurately measure AFR after the cat?
Several other sites suggest that the reading after cat will be 0.5 leaner than what it actually is consistently, while others say that it will be completely off.
Suggestions/thoughts?
Last edited by TheWulf; 10-08-2009 at 05:00 PM. Reason: added more info
10-09-2009, 12:05 PM
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Alright so after a week of two threads in two forums, I called Bosch directly and spoke with one of their techs.
The tech assured me that putting the sensor after the cat is futile. The sensor won't be accurate in that location.
He also mentioned that since this is a heated sensor, (which heats up to about 1400F according to the Prosport site), it should not be burning out if placed less than 18" from the exhaust port. He did mention however that it should be placed as far away as possible from the exhaust port if distance is limited.
There you have it.
The tech assured me that putting the sensor after the cat is futile. The sensor won't be accurate in that location.
He also mentioned that since this is a heated sensor, (which heats up to about 1400F according to the Prosport site), it should not be burning out if placed less than 18" from the exhaust port. He did mention however that it should be placed as far away as possible from the exhaust port if distance is limited.
There you have it.
10-09-2009, 01:23 PM
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Not sure I can use the current gauge with another controller though.
I suppose I'll use my current setup until I run into problems and if it's too much of a PITA then I'll ditch the Prosport and do a different gauge.
I suppose I'll use my current setup until I run into problems and if it's too much of a PITA then I'll ditch the Prosport and do a different gauge.
10-13-2009, 01:11 PM
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Prosport has a little box marked UEGO Controller which takes 3 connectors (gauge, power, sensor). I assume the gauge is just a display that takes a signal from the controller.
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