O2 Sensors

[Music] in this video we'll be talking about standard oxygen sensors now what we deem a standard auction sensor the one that has been around for a long long time now really there are two main types there's a zirconia sensor and a titanium sensor do you really need to know how they're both built i don't think that's that important for our discussion you need to know they both exist they're a little different they're not interchangeable now the titania was really only used for a few years i don't know anyone that's currently using it and so we're not going to talk about that one just know some older nissans used it some jags used it few other cars used it but wasn't in widespread use the zirconia now that one was actually very common still is you still find it in cars today in fact pretty much every post cat oxygen sensor is still a standard zirconia o2 sensor even if it has wide range or wideband sensors pre-catalyst now the zirconia sensor it actually acts a lot like a battery and will and those of you that like to be technically correct will call me out on this but we're just going to say that it creates its own voltage and it does this through a catalytic reaction inside the sensor itself it's a difference in oxygen now it also needs some hydrocarbons to make this happen that's why i say it's a catalytic reaction need some hydrocarbons and some oxygen and it samples that oxygen it samples a difference in the oxygen inside the exhaust stream and outside of the exhaust stream if we happen to have low oxygen in the exhaust stream especially relative to atmosphere which is 21 02 for those keeping track if we have a high oxygen content outside and a low oxygen content inside the exhaust pipe we have a great differential okay first off why would we have low o2 inside the exhaust because we had more fuel than air we used all the air up trying to take care of the fuel a rich condition so we have low o2 a rich condition that means we have a high differential in the oxygen inside and outside of the exhaust pipe that's going to create a relatively high voltage from the sensor this sensor produces 0 to 1 volt if we have a very rich condition we're going to be up close to one volt now on the flip side of that if we have high oxygen in the exhaust pipe like close to 21 percent okay it doesn't have to be that high but if the differential is not as great if we have high oxygen inside the exhaust pipe high oxygen outside the exhaust pipe then it's fairly neutral or balanced out then we're going to have a low voltage output from the auction sensor or close to zero volts now really what we might consider the oxygen sensor is is a stoichiometric switch it's a stoichiometric switch now stoichiometry we'll keep it with the automotive version that's when we have the right amount of two or more substances for com that are going to give us complete combustion so in our case if we're talking gasoline gasoline has a stoichiometric air fuel ratio of 14.7 to 1. so if we have 14.7 parts air and one part fuel inside that cylinder under the right conditions theoretically it should burn completely consume but that's not proper it's going to rearrange everything because the whole conversion of matter right but it's essentially going to consume all of our oxygen and hydrocarbons i.e gasoline in the process now that's in the theoretical perfect world which we don't live in but that's for you to know is that if we talk about stoichiometric air fuel ratios we mean one where we have the exact correct amount of fuel and air to give us a theoretical perfect burn now in our standard oxygen sensor if we are at a stoichiometric air fuel ratio or our correct amount that sensor will sit at about 450 millivolts are just about exactly halfway in its range but that sensor isn't built to work like that it's built to switch continuously it can't just sit at 450 millivolts it won't work it would keep wandering up and down so what we do is we force it to switch and we do it very rapidly and what we're looking for is for that switch to go to at least 700 millivolts and then drop down to 300 millivolts and back up to 7 and back down to 300 it can go a little higher it can go a little lower but as long as it's switching up and down up and down up and down continuously then that's going to average 450 millivolts and we will be right about a stoichiometric air fuel ratio now that switching has to be even so even if we go up to 800 millivolts if we stay up there for a long time then come down and only spend a split second down at 150 millivolts and we shoot back up and hang out for a long time at 800 or 700 or 950 that air fuel ratio is going to average rich so what we need to do is make sure that we are even in our switching up and down now i said that 450 millivolts was technically our stoichiometric breakeven point right where we want to be what's important in our standard o2 sensor is once we get above 450 millivolts how rich is it i don't know it's richer than a stoichiometric air fuel ratio meaning we have less air more fuel than we theoretically need below 450 millivolts now we have to lean of a condition how lean is it i don't know it could be 15 to 1 could be 17 to 1 could be 27 to 1 i don't know we just know that anything less than 450 millivolts means that we are in a lean condition or leaner than stoichiometric our whole goal of the sensor is to switch above and below that 450 millivolts constantly and consistently when we're in closed loop operation so why don't we take a look at an example of that on the scan tool and the oscilloscope and you can kind of see what i mean so we'll look at that and come back to this in a second we're going to start with a scan tool capture here this is scan tool data that was taken during a road test and this vehicle is just being driven pretty normally at this point in time now first and foremost the thing about looking at an o2 sensor on a scan tool is that o2 sensors are an analog and relatively slow signal so if we're just trying to make some relative measurements and some relative inspection you'll actually find that the scan tool is perfectly acceptable for doing this for a lot of cases until we actually have to get into some more precision measurement and what we can see going on here is that if you look here's our voltage on the left side and you'll notice that the sensor actually got as low as 61 millivolts that was its lowest at the bottom it usually averages you know probably around 80 or so on the low side switches up to the high side and we're clearing 800 going you know about 820 or so it hit a peak of 833 so this is pretty normal you can see that we switch quite often here's 450 is going to be right through about the center of this so we have some good switching it's fairly consistent it's really a pretty normal looking o2 sensor as far as scan data goes now i'm going to throw out one caveat here this is a snap-on capture and like a lot of scan tools where normally we would have time on our other axis here on our horizontal axis what you see here these numbers these are actually frames frames of data so don't try and use this on a scan tool this horizontal axis don't try and use this as a time axis now let's go ahead and take a look at a scope capture so we're looking at a lab scope capture of our same oxygen sensor pattern now you'll notice that it really doesn't look that much different than it did on our scan tool the biggest difference being is we've recorded a lot more data points so now if we want to zoom into this in a little bit and we will you'll be able to see a whole lot more detail we can't do that on the scan tool we can only get a picture about like this maybe a little bit finer but not much but right here you see we have some good even switching if i take one of my cursors and i run it right about through the rough middle of that i am right about 437 438 millivolts we're looking for 450 and i pretty much guessed it there so that looks pretty good it looks pretty centered we're doing okay if we measure across the top kind of an average there and we'll go ahead and measure across the bottom you'll see that our scope caught this switching it dropped to about 73 millivolts in the low side about 833 on the high side that's doing pretty good this is a decently working sensor so now that we've taken a look at our scope and scan tool captures now we're going to dig back in real quick we're going to look back at a scope capture and what i want to show you is the transition time when that sensor is truly working as it should be we want that transition from low to high or high to low so that roughly 300 to 700 no if we were really good 200 to 800 but at least at 300 to 700 millivolts we want to see it make that rise in less than 100 milliseconds and the same thing on the fall on the other side we want to see it drop from seven to eight hundred millivolts down to two or three hundred millivolts in under 100 milliseconds that means that our sensor is working okay now the sensor can switch much more slowly than that on a good working sensor if the computer is causing it to happen so be cautious here if you have a sensor that you're unsure about and you're testing it with an oscilloscope don't just call it bad because you saw it switch at that rate make sure it's fully warm which we'll talk about in a couple minutes and make sure that you've forced it to switch as fast as it can so add a whole bunch of fuel in a hurry snap the throttle open yank a vacuum line do something to force it to work quickly and then measure the results there were a lot of older asian cars that switched very slowly at an idle and that was normal that's just how they worked the sensor was fine there was nothing wrong with it so again we'll look at it and you're going to see that a good sensor so just make that that transition in under 100 milliseconds all right so check that out i'm going to zoom in on just one switch roughly and i've already set up the cursors to measure this out now i prefer to measure 200 to 800 millivolts so i actually do have to tweak this just a little bit so if i take this lower cursor and i'm going to set it right at 200 millivolts you can run this 300 to 700 i really prefer two to eight um and i can't quite make 800 on the top so i'm just going to put it at the upper part of the switch right here right when it pretty much topped out so i'm at 200 here i am at almost 800 on the top now i'm going to bring my time cursors over and i'm going to set them up so that they intersect so my number ones right here it intersects that 200 millivolt mark my second is going to go right here it's going to intersect that almost 800 millivolt mark and i'm going to look at my delta time between the two that's in this box right here and i'm going to see that that delta time is just under 55 00 milliseconds i needed to be less than 100 i hit it at 50 i'm pretty good so this is the rise now let's see what the fall looks like and again we also want that to be in less than 100 milliseconds let's see here i need to unlock those so we're going to move that one over there so once again you see this intersects in the waveform right there we've intersected the 200 millivolt line there i'm intersecting the roughly 800 millivolt line there and on the fall this occurred in about 64 milliseconds so that's pretty good we are on well under our 100 milliseconds realistically let me back up one a good sensor should be able to do one of those switches either lean to rich going up or rich to lean going down in about 35 milliseconds that's what a true good sensor should be now it's worth noting that i wasn't forcing this sensor right here this vehicle was just held at a higher rpm so it was switching normally at this point in time if we are concerned about a sensor or if it's anywhere near its 100 milliseconds or slightly over then we really need to make it a point to force the sensor we need to force it rich and force it lean rapidly like snapping the throttle and then suddenly letting off and then going back and measuring at that point in time how fast our reaction was all right so now that we've seen the rise in the fall time the important thing and i mentioned it a little bit ago it has to be hot to work properly cold o2 sensor doesn't work our oxygen sensor starts to work at right around 600 degrees fahrenheit its optimum temperature is about 1500 degrees fahrenheit so we have to get that sensor good and warm to work properly modern sensors are all heated now we have one two three or four wire sensors going back from when they started out the original one wire sensor was not heated it required the heat of the exhaust system to warm it up enough to make it work it usually was not a quick operating sensor it didn't have real fast switching the computers didn't need it at the time it was good enough next we went to a two-wire sensor which is really just a one-wire sensor with an additional ground back through the ecm or pcm then we go to a three wire sensor now we have our signal wire we have a ground usually for the heater at this point and we have a heating element built into the sensor itself and for the last oh 20 30 years okay maybe not quite that long at least solid 20 years or longer now we've had four wire sensors so now our sensor has a sensor wire a sensor ground we also have a heater power feed and ground and that's the most common sensor you're gonna see now is the four wire sensor we have to get that sensor hot we have to make it work there's no way we can pass emissions without it the other thing too though is when we first started getting four wire sensors when you turn the car on they would get a power they were grounded usually the ground was solid and they're grounded through the body of the sensor so you'd power the car up it would have its ground it would just come on heat up the sensor and be working newer sensors newer technology now we know that once we get it warm that's a waste of power not only that there are operating modes where the exhaust may be generating enough heat to keep the sensor working anyway so now you'll find different strategies depending on the auto manufacturer but there will be a lot of o2 heaters that are now pulse width modulated on the heater side so they're going to control it they may give it a really high pulse width when it's cold to bring it up to temperature in a hurry and then once they actually get it heated up and it seems to be working normally switching fine they'll back the pulse width off to maintain just enough current through the heater to keep it at a good operating temperature without wasting power the really important part about that one is that sometimes they may even turn that off again if they think there's enough heat in the exhaust stream to make it work they may even turn off the pulse width to the heater and just let the heat of the exhaust do the work just remember if you're looking at scan data and you see sensors do something you think is funny like shut off a pulse width turn off a heater but you have no codes and you don't really have any problems with that sensor that's usually a normal operation so let's take a quick look at a little bit of scan data or something you might see if you are actually checking out one of these sensors what we're looking at side by side right here on the left you're looking at a picoscope capture of the circuit for the o2 sensor heater on the right we have a scan tool capture showing us that same circuit or at least what the the scan tool is able to show us from what's pcm's telling it now there's much more time on the scan tool capture than there's in the scope capture so i'm going to scroll the scope capture along right here you think it doesn't really look like much but what it really is showing us is it's holding that sensor to ground so i'm on the triggered or ground side of the heater or the heater circuit for that sensor it's holding it low so this is a 100 percent duty cycle it's got power applied to the other side it's fully grounded on this side it's flowing full power that's what you're seeing when it turned on right in here you're seeing it ramp up and hold that power but now once the heater starts to warm up and it doesn't need as much power as much amperage to maintain itself and to keep it working properly you're going to see the amperage that's what's represented in the scan tool capture over here on our vertical scale the amperage is going to drop over time to do that if we look at the circuit through the lab scope it's going to start duty cycling it it's going to start pulling it off ground and giving it a little time where there's no power flowing in the circuit so every time it comes off ground that's actually depowering the circuit because we had power applied to the other wire so as you see it duty cycle on our on our scope capture here on the ground side of that sensor that's the same spot where our our amperage is dropping off all the way through here until it drops down about 450 milliamps and kind of hangs out there they're going to do this so that the sensor has just enough power to stay at its operating temperature but not so much that we're wasting energy we don't need to overheat it the exhaust stream will help keep it heated up and we're going to duty cycle it to just maintain that temperature and do it at the optimal power supply so this is kind of what you'd see on a later model o2 heater that's pulse width modulated that's what's going on right here that's our pulse width modulation okay the last thing i'm going to leave you with some removal and installation first off we have a lot of special tools that we can use for getting auction sensors out and where they're located a lot of the times these are a good thing sometimes they're super simple you put a 22 millimeter 7 8 wrench on it crank it right out other times we need some specialty sockets to get in there my warning to you this sensor is in the exhaust system this sensor has lived in that exhaust system for sixty eighty a hundred and fifty two hundred thousand miles there are many times when the threads of that sensor become gulled or seized into the exhaust pipe so at the very least we may have to get the torch out and heat that sensor up dramatically in order for it to break loose and remove it so we can replace it now when we have to do that usually the threads are damaged as well most of the time that's fixable but we have to be very cautious tap that back out clean it up before we even attempt to put the new sensor in if the threads are damaged don't just try and jam a new sensor in all you'll do is damage the threads on the new sensor also when it comes time to put the new sensor in they come with a little tube of anti-seize in the package of almost every oxygen sensor you buy there's a reason for that use anti-seize on the threads of the sensor when you install it that'll help hopefully keep it from going in that exhaust pipe so maybe if it has to get changed again in the near future it'll come out more normally and with that we'll catch in the next video [Music] [Applause] [Music] so [Music] [Applause] [Music] so [Music] [Applause] [Music] so [Music] so [Music] so [Music] [Music]

Channel: PCC AST Engine Performance

Views: 44,358

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Id: THRcjGmHAh0

Length: 25min 3sec (1503 seconds)

Published: Wed Nov 04 2020