The Trainer #70 - EVAP Testing Tips

did you know that the evap DTC's or the evaporative emissions diagnostic trouble codes are among the top ten that we deal with on a regular basis and the most challenging of these to find and correct are the ones associated with leakage which stick around that's the topic we're going to tackle today on the trainer before we get started on today's topic let's first talk a little bit about what the evaporative emissions system does and how it works first let's start with what it does we all know that their emission standards set for the vehicles that we service we tend to focus though on the ones coming out of the tailpipe this is the carbon monoxide and HC that we worry about now HC what is that hydrocarbons and what do we also know hydrocarbons as unburned fuel so there are standards for the amount of hydrocarbons that are allowed to pass through the exhaust we usually measure it in parts per million don't we when we're using our five gas analyzer and these are where the standards are set but where else on the vehicle is there a source of HC the fuel tank fuel tanks full of unburned fuel in it and it's not the liquid that we're worried so much about it's the vapors we have to control the release of fuel vapor to the atmosphere right from the point of the filler neck all the way to the engine where it's finally used in the combustion process that is the role of the evaporative emissions system to contain and control those fuel vapors and just like the tailpipe emissions there are standards set for what is okay and what's not okay and we reference it by the size hole that would be present that would allow excessive HC to escape today we know that as the PIO 456 small leak detected the twenty thousand seven inch orifice size that would allow a too much HC to escape would be enough to turn on the light and warn the driver there's a problem with his emissions now let's just kind of think about that for a moment twenty thousands of an inch well the first thing I want you to know is there's nothing in the rule book that says that has to from one place you could have multiple leaks that add up to a loss equivalent to a twenty thousand seven inch sized hole now how much is that well here's what Bernie Thompson said an article he wrote for us not too long ago he said think of a dime a dime weighs a little less than two and a half grams not a whole lot a dimes worth of HC can escape through a twenty thousands of an inch hole over the period of a few miles and that doesn't sound like a whole lot does it but consider that that amount of HC loss that amount emitted to the atmosphere is thirty times more than what we allow out of the tailpipe and now you can see that finding and fixing even those small leaks is very very important let's move on to talking about how the evaporative emissions system works now I know yeah there are as many variations it seems as there are stars in the sky every OAM has what seems to be their own little take on it and you're right there are some nuances from manufacturer to manufacturer that you absolutely want to take a look at before you perform any serious diagnostic work but there are also some commonalities there are some essential components that all these systems share and they all have to do the same thing contain the vapors so let's start with exactly where those vapors are contained fuel vapors are trapped in a component called the charcoal canister or EVAP canister these are typically located underneath the vehicle near the fuel tank now why the charcoal canister may appear to be a simple device it is rather complex and there are some things that can come into play when you're diagnosing a problem with the system first the canister contains kernels of activated charcoal it's this activated charcoal that actually adds orbs not absorbs adsorbs you know the fuel vapors and and holds them in place now there is a limit to what a charcoal canister can hold so there's a problem for example of raw fuel getting into that canister that canister can become damaged very very quickly another factor that comes into play is the vehicle use a vehicle that suffers a lot of severe off-road kind of duty heavy lot of dirt roads bumping and bouncing can cause those kernels to become pulverized which again reduces their ability to contain the vapors it can also cause the positioning walls inside the charcoal canister to fracture which would allow some of those kernels to escape to parts of the system where we really don't want them and another factor that comes into play is when the fresh air vent becomes damaged and allows dirt and other debris to enter the canister and and further reduce the amount of flow possible through the canister so there's a lot of factors you want to consider when you're inspecting that component now as I mentioned the charcoal canister can only contain so much fuel vapor we have to get rid of the vapor from the canister we can't release it to the atmosphere so what are we going to do with it well we're gonna draw it into the engine and allow it to be burned with the rest of the unburned fuel that we're sending to it through the fuel rail that's controlled by a component called the purge valve now it may go under different names depending on manufacturer but essentially the role of the purge valve is the same it's controlled by the ECM typically through a pulse width and the duty cycle will be dependent on what the ECM thinks how how much fuel vapor it thinks it needs to withdraw from that canister and get into the engine we can't do too much at one time can wait because then we'll start affecting the fuel mixture and the fuel trims and that's going to skew those numbers we can't do too little or we won't get the canister clean so the ECM controls that valve engine vacuum is then applied to the canister that draws the vapors into the engine to be burned only one problem with that though if we open the purge valve and start applying vacuum to the canister it's not going to take very long to create a balance in the vacuum in the system and then all flow is going to come to a stop in fact we could cause some damage to the lines if the vacuum applied is greater than that line can handle so we have to have a way to keep that that balance we want flow air flow through the canister so what we're going to do is we're gonna add something in the back door it's called the vent valve and this allows atmospheric air into the canister when the purge valve is open to help draw those vapors into the engine without causing any issues in in the system those are the components that make up the foundation of the evaporative emissions system now let's talk a little bit about the onboard testing of that system again with a focus on leaks essentially all we really need is some way to either change the pressure in vacuum in the system and monitor that pressure in vacuum for loss fairly simple right most systems made by the OEMs today use a vacuum as a preferred testing method but there are a few that use pressure those that stand out in mind are the Chrysler LDP or leak detection pump and BMWs D MTL system most of the others use vacuum as their theirs preferred way of checking the system so what do we need to do that well we need some way of measuring the sensor or the pressure in the tank or vacuum in the tank and that's going to be at the fuel tank pressure sensor now how are we going to create or monitor that how are we going to run the system through the steps the first thing we're going to do is we're going to open up the purge and the vent and there we're going to make sure that we have the ability to draw a vacuum through the system what we should see in the pressure sensor is just a real small vacuum develop when both valves are opened once we know that we can actually pull a vacuum on this system we're gonna close the vent solenoid and we're going to leave the purge solenoid open now we're going to draw the system into a vacuum to a specified point again as monitored by the fuel tank pressure sensor once we've reached that point we're going to close the purge solenoid and now we're going to watch the signal from that pressure sensor we're going to be looking for vacuum decay does it hold depending on the rate of decay is a measure of how big that hole size is and that's what's going to end up turning on the light okay here's a diagnostic tip for you when you're faced with one of those especially small leak challenges that you can't find the leak there may not be one for you to find one of the factors that comes into play is how much fuel is in the fuel tank and has the ECM know it goes by the fuel level sensor if that's providing an inaccurate reading that could provide inaccurate data for the ECM to use in performing that leak test and that could result in a ghost code that really doesn't exist so consider that when you're chased with that problem is that fuel level sensor telling the truth or isn't it and while you may run into those really tough ones from time to time the majority are not going to cause you that much difficulty if you remember these three keys to success make sure like we told you on every other diagnostic that you understand the system that you're working on and how it operates second thing do your homework and understand what the diagnostic trouble code is what's the state enabling criteria how does the ECM know when to turn the light on how does it test for that particular malfunction and then last but certainly not least though your diagnostic equipment vitally important if you're going to have success finding those especially small leaks I'd like to move on now to talk a little bit about the tools and techniques that you can use to help you find those small leaks but before I do there's a couple of things that I want to stress we just went over the general process used to test these systems for leaks and that was relying on the fuel tank pressure sensor wasn't it first of all keep in mind that pressure and vacuum changes in this system are very very small they're measured in single digits and for example vacuum in the system not measured in inches of mercury like we're used to seeing on your vacuum gauge is measured in inches of water so it's very very low levels of vacuum and/or pressure that we're trying to detect here and because of that because that small leak can cause such minor fluctuations a lot of the OEMs have specialized processes that they use specifically for testing for those small leaks so make sure like we said earlier on the very first thing you have to do is make sure that you're clear and exactly how the system you're working on tests for leaks so that you know what you need to be looking for and once some areas may be affected that really aren't a leak at all maybe it's about that particular component that's improperly located or has a problem internally or something along those lines another thing of course we want to check is technical service bulletins a lot of promise with the vehicle setting the small leak codes are a result of an error in the programming and there's a flash out for that to correct that problem turn the light off all right so what we're gonna get we're going to focus on tools and equipment techniques for finding the leaks general process and where the first things we're going to talk about is your scan tool now there are a lot of scan tools on the marketplace today many of us use aftermarket tools that have what we call enhanced data for the model lines that we service most commonly and you've heard me say number of times that I can successfully diagnose most obd2 problems ECM powertrain problems using a global OB to scan tool or not really need e enhanced data but here for e batch systems I'm going to encourage you to make sure that you have the enhanced data available for that model line why is that two reasons first a lot of the data that you're going to want to look at to help either find the leak or verify that you fix that leak there's only going to be available to you in that enhanced data list the second thing that you're going to want to have enhanced data for is for the system tests and the bi-directional controls that you may need either as outlined by your system information and troubleshooting information again to either find or verify that you've properly fixed that leak now one of the things that you're going to have to do in order to test the system for leaks is seal the system now remember the sill annoys are the vowels that we talked about early on the purge and the vent well typically the perch solenoid is closed and the vent solenoid is open well I can't test the system by applying any kind of pressure to it can I unless I have the system sealed so I may be able to use the bi-directional controls and enhanced mode to close that vent solenoid without having to do anything fancy and then seal the system and start with my leak test but here's a tip for you if you don't find it in your enhanced data you still can check global obd2 specifically mode eight that's control of onboard system and for the most part if it's available it will allow you to do what I just said close the vent solenoid so you can perform your evap leak test now neither one option is available you're going to have to use another method in order to close that solenoid and proceed with your test let's talk about leak testers next the next piece of equipment that I want to talk about is your evap diagnostic machine commonly referred to as your smoke machine now there are several on the market I'm not trying to promote one or the other I just happened to be using the smoke wizard today as the example in this this session but it's got some nice features on it that you should look for first I have a flow gage that can help me determine whether or leak is present or not and I also have a combination pressure vacuum gauge again in inches of water so that I can help look for the decay rate just like the ECM does again looking for those very small leaks there's a flow control on the machine the first question we want to answer is what do I connect to the inlet side of the machine many of you are using your shop air to do that and I'm gonna tell you I don't personally prefer that a couple of reasons why number one I don't know how clean my shop air is so I don't want to do anything to harm my equipment in the process I don't want to be dumping oil or water or metal particles or whatever else might be in that shop line you know to get into my machine so that's one number two many manufacturers caution you against using compressed air because you're mixing air with fuel vapors you can create a more explosive atmosphere than was there to begin with it's a safety hazard a potential safety hazard so why bother with that when another answer is very very easy to do use an inert gas like nitrogen or my preference is co2 in fact this machine actually comes with the adapter so that you can take a 20 ounce bottle of liquid co2 the kind that you can buy at any paintball supply store and connect this to the Machine and use that as your gas source and there's a couple of good reasons for that too first we avoid that flammability issue by using co2 the second one is the co2 molecules are much smaller than the molecules that you'll find in shop air the the mix and because of that co2 will escape from a small hole when maybe air won't and it makes the leak that much more difficult to to verify and of course spot when you start putting the smoke to it the next thing I'm going to tell you is don't go right off the gun and start pumping smoke into the machine into your system you know make sure that you verify the leak exists first or you're just kind of spinning your wheels and wasting your time also keep in mind that the molecules in smoke a couple of drawbacks that may cause you a challenge in finding that very small leak or that leak source because these are petroleum-based products typically the cannister supposed to absorb hydrocarbons right it excuse me at sorb hydrocarbons so some of the smoke may be trapped in the cannister and not get to the leak source other things that you might run into with the smoke again is the size of the molecules in this and the product that makes up the smoke it may be too big to get out of that hole like I said the very beginning the spec is twenty thousand seven inch but that doesn't mean that it's one your small leak code is set by a twenty thousand soar bigger hole there could be multiple holes that are causing that leak rate and you may not find those smaller combinations using shop air and or using smoke so that a few things are considered there but for the most part you'll be able to find a majority of them using you know a good quality evap tester like this one now let's talk a bit about the technique here's what I like to do with my machine once I go ahead and get it hooked up to the system I'm gonna turn it on and you're gonna notice that it takes a while for the ball to start coming down and that's because I got to fill all the air space that's in the system the lower the fuel level in the tank the longer it's going to take to fill that space again another tip from Bernie Thompson's article that he wrote for our magazine if you want to get an idea of how long it takes to fill that space take a clean five-gallon container and then use your equipment to fill that container and you're gonna have to do that times while you time it and when you see the ball drop all the way to the bottom indicating that the system's been filled and there's no leaks count that number of seconds and use that as a guide so for example if I have a 20 gallon tank specified for the vehicle and I'm looking at and it's half-full according to the gauge that's 10 gallons that's divided by 5 that's to show every time I counted let's just say 10 seconds times 2 20 seconds is what it should take to fill that dead air space give or take a few that can give me an idea if there's a restriction in the system maybe the fuel level sensor is inaccurate something is anything like that that was just gonna raise a flag that can help me find that small leak a little easier so that's not a bad baseline measurement to use now once it has gone all the way the bottom first if it bounces around like you see here well certainly that indicates that I have a leak it's not it's large enough where I'm not going to get the pressure all the way to the bottom but if I have a situation like this one what I do have it now all the way at the bottom ok now I can turn off the system and I can monitor the pressure gauge and watch for decay if I start to see that being lost almost immediately then I have a leak it might be small but I do indeed have a leak and now I can proceed with more precise troubleshooting ok so let's just say that we've got our smoke machine hooked up and we noticed that it got down to the bottom the ball flow valve got down to the bottom flow stopped and an expected amount of time so we don't expect there's any problems with the fuel level sensors there no TS B's but we're monitoring the the decay of the pressure of that pressure that we put in the system and we see that it is losing pressure we know we have a leak and we have a small one those are among the most challenging of course to find as I stated earlier already a couple of times the standard is 20,000 seven-inch but that doesn't mean that it's always going to be 120 thousands of an inch or bigger hole that you're trying to find it could be multiple smaller holes that are giving the same leak rate so what I would encourage you to do is once you've determined that yes there is a leak we can see the decay I've proven that break the system up into come in two parts for I would break it up into the Perseid in the vent side with the canister in the middle I would take the lights loose at the canister and I would close off the purge side and apply that pressure again and monitors see if the same amount indicated returned if it did well I know that that's the side of the system I need to focus on with the smoke test to find out where exactly it's leaking from if it didn't well I'm okay with that I can set that off to the side and I can move on to the other half of the system so break it up into components and check the components individually keep in mind that when you're checking the filler side of the fuel tank that many vehicles have that rollover valve in place so that when you apply pressure to the tank you're going to close that rollover valve and that's going to keep your test pressure from going any further so you want to make sure that you are testing the fuel filler and the cap you may actually have to go in from the fuel cap side and what we're talking about the fuel caps resist the urge to immediately check to see if the cap is tight sure inspect it if it's missing completely well then you have idea of where that leak code came from but that small leak could be caused by a bad sealing the cap that you're gonna fix without knowing it when you go in there and just give it a couple of clicks so resist that temptation verify what the problem is first and then if you see that small leak you want to give it a couple of clicks to see if it goes away that's okay that I wouldn't have a problem with and you'd be not wasting your time that way a few other things when you're checking for leaks I want to make sure you're aware of as I commented on in some cases the air that you're using is not going you're using shop air and that's not going to get past those small holes because of the size and the molecules involved if you're using co2 then the odds are yes it'll get past that small hole and you and you'll be able to get the leak detected that way again though the smoke may not begin again because of that molecule size so wouldn't it be neat if there was something we could use to sniff it out just like we do on an air conditioning system well there is it's actually part of the system that bernie thompson developed over automotive test solutions it's called the bullseye leak detection system hey this is not a promo guys but if something works I'm going to tell you about it this is co2 sniffer and it can come into play to help you find those leak sites when other methods have been leaving you hanging now I'm not saying that that's going to happen every single time there are many many many leaks that you'll fix just fine using the procedures that we've talked about so far but you're looking for that pesky small leak are those multiple leak sites that you can't find otherwise this tool will help you find it and because it detects co2 there are a lot of other uses that you can apply this this equipment to to Burney also developed a foam so that when the foam is sprayed on that suspected lee site it will actually change color in the presence of co2 just confirming you're on the right track so that's a tool that you might want to consider to help you if you're really trying to find those really really small leaks that are driving you crazy here's a few other tips for you when we're talking about trying to find those pesky small leaks one get yourself a lot of those little laser pointers you know the kind the kids like to play with cats with you can use that too to help spot leak and those hard-to-reach areas where you can't physically see it but we passed a laser through it you know kind of like the spy guys do when they're looking for where the alarm laser beams are and they spray that smoke over it well same thing but in Reverse so that can help you spot where the smoke is another common problem our selling oil valves either the purge or the event valve that stick when when they're in service so sometimes they're stuck or they're leaking just a small amount you can find this a couple of ways you can monitor that that pressure DK like we talked about earlier as you operate those valves repeatedly and if you're going to operate the valve use your multimeter and amps mode and what I mean by that is if it's a ground controlled cell enoyed say a vent solenoid and you want to check it for a problem then you can ground the site side of the solenoid through your ammeter to a chassis ground then you can just repeatedly on and off on and off don't leave it connected from long okay you're going to overheat and damage the valve but you can click it on and off on and off on and off several times a few dozen times and then watch the current okay if there's a problem electrically won't you see that in the amount of current flow you know if it starts to heat up and goes open well you'll see a change in current flow so that's one way you can check it you can also again monitor that that decay rate and if you keep a pressure applied to it if it builds and goes away builds goes away builds goes away and that doesn't build again because now it's not closed that could be another giveaway sometimes simply just blowing on it making sure that it goes one way and doesn't go the other as a test but keep in mind that those inner minutes will affect you and like I said before first and foremost check your system operation make sure you're clear on that check the TS B's you can also check your other resources but if you do find that silver bullet by doing a research on through any of the portals that are available make sure that you verify before you just jump to that as the solution remember our motto test don't guess that's all the time I got for this edition the trainer I hope you found it helpful I'll see you next month [Music]

Channel: Motor Age

Views: 128,006

Rating: 4.8116207 out of 5

Keywords: #automechanika, chicago, motor age, the trainer, automotive repair video, car repair, auto how to, how to fix my car, auto tech, auto technician, auto service professional, engine performance, auto electrical how to, automotive drivability, obd 2, obd II, onboard diagnostics, auto computer, voltage drop, ohm testing, voltage testing, evap leak test, evaporative emissions, p0455, p0456, p0440

Id: IuyGeQLTF9U

Length: 25min 41sec (1541 seconds)

Published: Wed Sep 27 2017