DrNick
03-13-2009, 09:12 AM
I'm not really sure which section to post this in so that it stays there as a reference. Mark you may want to move it if I put it in the wrong place :)
Since there seem to be a lot of questions on this topic I thought I would bench test a denso oxygen sensor to illustrate what happens when it is in use. This discussion is for narrowband sensors only.
First off , we can't go past the wiki description of what they actually do for us.
Automotive oxygen sensors, colloquially known as O2 sensors, make modern electronic fuel injection and emission control possible. They help determine, in real time, if the air fuel ratio of a combustion engine is rich or lean. Since oxygen sensors are located in the exhaust stream, they do not directly measure the air or the fuel entering the engine. But when information from oxygen sensors are coupled with information from other sources, they can be used to indirectly determine the air-to-fuel ratio. Closed-loop feedback-controlled fuel injection varies the fuel injector output according to real-time sensor data rather than operating with a predetermined (open-loop) fuel map. In addition to enabling electronic fuel injection to work efficiently, this emissions control technique can reduce the amounts of both unburnt fuel and oxides of nitrogen from entering the atmosphere.
Good isn't it :)
Now, there are a few types of sensors around - The most common is a Zirconia type device. This was another one of Bosch's inventions. The device generates an electrical current which varies based on the amount of oxygen in the air. Sound simple? Well it is really. Almost all OEM narrowband sensors generate this voltage in the range of 0-1V. This means that they are very often interchangeable.
The first thing to note is that they only work when heated to the correct temperature. Usually the exhaust gases do this job fine, but it means that the readings you get from your sensor will be wrong until it reaches the correct temperature, i.e after the car has been running for a few minutes. Now, from an emissions point of view this is terrible as you can imagine a cold engine with lots of extra fuel being burned isnt really the most efficient thing, and the ECU has no way of trimming fuel unless it has a valid O2 sensor signal - Hence the introduction of the heated sensors. Most of us have an engine with the single wire sensor which is unheated, the later models seem to always have multiple wires as they include a heating element.
Aside from the heating element, the sensors are still the same . So it is fine if you want to upgrade to a heated O2 sensor next time you replace yours. Just make sure that you wire it in properly so that it gets its power and you're set.
The second thing that you need to keep in mind is that the response from a narrowband is NON LINEAR. This basically means it is either saying rich or lean. It does not have the ability to let the ECU know how rich or how lean it is. This is why they are useless for tuning.
Here is what the response of our oxygen sensors looks like
http://www.stealth316.com/images/o2sensor-output.gif
As you can see, it is pretty useless for tuning as it will have almost the same output at 11AFR as it will at 13AFR!
Here is some info from Toyota showing emissions curves
http://www.stealth316.com/images/fic-af-emissions.gif
Now, if you want to test out an unheated sensor all you need is a place to hold it and a blowtorch to heat it up. Set the volt meter on the milliampere scale and watch what happens.
This is a bench test of a Denso single wire sensor that I did this morning.
As you can see, there is no output for ages until the sensor heats up. After that the blowtorch is doing 2 things, heating the sensor and also depleting the oxygen in the area at times. If you look at the voltage being generated though you can see it rarely stays on any intermediate values it is usually either very low or very high. This is exactly what it does in operation in your exhaust manifold.
http://www.youtube.com/watch?v=ItnKP-XKaZo
I hope this will answer some peoples questions :)
Since there seem to be a lot of questions on this topic I thought I would bench test a denso oxygen sensor to illustrate what happens when it is in use. This discussion is for narrowband sensors only.
First off , we can't go past the wiki description of what they actually do for us.
Automotive oxygen sensors, colloquially known as O2 sensors, make modern electronic fuel injection and emission control possible. They help determine, in real time, if the air fuel ratio of a combustion engine is rich or lean. Since oxygen sensors are located in the exhaust stream, they do not directly measure the air or the fuel entering the engine. But when information from oxygen sensors are coupled with information from other sources, they can be used to indirectly determine the air-to-fuel ratio. Closed-loop feedback-controlled fuel injection varies the fuel injector output according to real-time sensor data rather than operating with a predetermined (open-loop) fuel map. In addition to enabling electronic fuel injection to work efficiently, this emissions control technique can reduce the amounts of both unburnt fuel and oxides of nitrogen from entering the atmosphere.
Good isn't it :)
Now, there are a few types of sensors around - The most common is a Zirconia type device. This was another one of Bosch's inventions. The device generates an electrical current which varies based on the amount of oxygen in the air. Sound simple? Well it is really. Almost all OEM narrowband sensors generate this voltage in the range of 0-1V. This means that they are very often interchangeable.
The first thing to note is that they only work when heated to the correct temperature. Usually the exhaust gases do this job fine, but it means that the readings you get from your sensor will be wrong until it reaches the correct temperature, i.e after the car has been running for a few minutes. Now, from an emissions point of view this is terrible as you can imagine a cold engine with lots of extra fuel being burned isnt really the most efficient thing, and the ECU has no way of trimming fuel unless it has a valid O2 sensor signal - Hence the introduction of the heated sensors. Most of us have an engine with the single wire sensor which is unheated, the later models seem to always have multiple wires as they include a heating element.
Aside from the heating element, the sensors are still the same . So it is fine if you want to upgrade to a heated O2 sensor next time you replace yours. Just make sure that you wire it in properly so that it gets its power and you're set.
The second thing that you need to keep in mind is that the response from a narrowband is NON LINEAR. This basically means it is either saying rich or lean. It does not have the ability to let the ECU know how rich or how lean it is. This is why they are useless for tuning.
Here is what the response of our oxygen sensors looks like
http://www.stealth316.com/images/o2sensor-output.gif
As you can see, it is pretty useless for tuning as it will have almost the same output at 11AFR as it will at 13AFR!
Here is some info from Toyota showing emissions curves
http://www.stealth316.com/images/fic-af-emissions.gif
Now, if you want to test out an unheated sensor all you need is a place to hold it and a blowtorch to heat it up. Set the volt meter on the milliampere scale and watch what happens.
This is a bench test of a Denso single wire sensor that I did this morning.
As you can see, there is no output for ages until the sensor heats up. After that the blowtorch is doing 2 things, heating the sensor and also depleting the oxygen in the area at times. If you look at the voltage being generated though you can see it rarely stays on any intermediate values it is usually either very low or very high. This is exactly what it does in operation in your exhaust manifold.
http://www.youtube.com/watch?v=ItnKP-XKaZo
I hope this will answer some peoples questions :)