Diagnosis + Understanding EVAP Systems (SBQM Full Video)

all right guys got a special treat for you just to show that I love all my viewers equally because I really do many of you guys have been here from the beginning I've been accused of some of the videos recently being teasers for my other channel Schrodinger's Box quantum mechanics where we do a lot more intensive diagnostics and especially training and what we're gonna do in this video is I am going to give you a full unedited video from Schrodinger's box quantum mechanics this type of video would only be available on that channel normally but I'm going to give you guys the full video first of all so you can get a taste of what you're missing if you're not a subscriber on my website over there I will put a link in the description but also this video happens to be the single most requested video in the history of the channel and that is the diagnosis and understanding of evap systems quick note for my viewers in third world nations and developing countries all you have to do is notify me and I do a quick validation and I will give you free access to Schrodinger's box quantum mechanics I know that's a very important part of many of your guys automotive education if you do this professionally because you don't have schools out there I came to find that out so let's get started with the video I hope you enjoy it [Music] [Music] [Applause] alright guys we are going to do a video that is long overdue the diagnosis and understanding of evap systems the reason being that as mentioned in the previous video I have a Buick Century coming in that actually has a rich condition problem and for some reason it doesn't have a check engine light the car dies at idle almost like you'd expect with a vacuum leak except I did in the field diagnose it is due to a rich condition I've already ruled out fuel pressure regulator and I'll show you how I did that but what I'm going to do is I'm going to run through all my rich condition variables but I have a suspicion this is an evap problem even though we're not getting a check engine light for it and of course part of my rich condition variables is going to be an evap system test you'll need to understand what I'm doing during those tests with the evap system thus the reason we're going to proceed it with this video so let's get over to the dry erase board of knowledge and let's master the evap system alright so one thing about evap systems is you're gonna find that as it usual once you understand them they no longer become serious and everything similar to understanding cam and crank sensors all that mystique goes away it looks very complicated but once we run through this it's not only actually fairly simple but you'll be able to very much understand the mechanics and design of it that would also what cause check engine lights and how it knows there's a small leak in a large leak in blah blah all of that so we're gonna understand all of that and with this diagram what we've got is anything in red is going to be electrical anything in green is going to be evap lines and hoses and then in black will be components which most of those I've labeled in blue ink that are specific to the evap system so once you understand this you'll also understand that it is a little difficult to explain when you understand this why I would suspect an evap system problem on this car with a rich condition and we wouldn't have an evap code the the PCM is pretty smart on these they take this very seriously on most models these evap systems and I will admit it's very unlikely you would have an evap system problem and it wouldn't be caught by the PCM and that will become apparent so before we go over the diagram the first thing of course what's the purpose of the evap system and the idea is that gasoline is you guys well know is very very volatile it has a lot of fumes that evaporate very readily and the idea with an evap system is back in the old days these fumes these vapors from the evaporated gas would just go off into the atmosphere well not only is that bad for the environment but it's also very wasteful because you can use those vapors to burn as fuel in the engine and actually it's extraordinarily efficient because it's already vaporized so that's the idea what the evap system is to capture these vapors which is done in this charcoal canister an activated charcoal canister which will capture those vapors and then under the right conditions the vapors will be released into the intake manifold to be burned as fuel so it helps with fuel economy helps with emissions all kinds of things like that that are beneficial so that's the purpose of the system now as far as the design of the system I know my artistic abilities I'm well familiar but it all makes sense if we break this down step by step so again red is going to be electrical green are lines and hoses and in black will be components generally labeled in blue so our first component of course is the fuel tank where the vapors are all going to originate from from the gas tank we have our filler neck here with our gas cap and also here is going to be a check valve so that when the fuel level reaches up to the full it assists with turning off that nozzle for the fuel pump so that you automatically have it shut off the gas cap is actually very important it seals the system this is a very important concept to understand as we go through this is that this is a potentially fully sealed system there's three points of sealing with it your gas cap your solenoid here before the intake also notice the purge solenoid and your vent solenoid and we'll talk about those but at some times all of these solenoids and of course your gas caps should be constantly closed should fully seal this system and that's one of the things the PCM looks for in order to do some of the Diagnostics we'll go over that later now again many of these systems are going to have some variances to them and I'll describe some of the variances but basically if you understand this one which is a typical GM system you'll understand them all but many of the systems will have a shutoff valve that basically is your source point for all of your evaporative emissions captures so your evaporative emissions will go up through the gas tank and then into the canister where it's stored for later use some of it also because you're going to have some cycling up here from the filler neck some of those fumes from the filler neck can also come back in here if you've ever removed the gas tank on a car you know there's usually another hose running up alongside the filler neck and that's what the purpose of that hose is now this shutoff valve is designed so that if the fuel level is too high if the car is moving or you overfill gas tank whatever then what can happen is of course you couldn't get fuel into the system and you definitely don't want to get fuel into the charcoal canister or into any other components of the system so this is a little float here that if the fuel level gets too high this float would increase in distance and plug off the evap line to prevent liquid fuel from getting in fuel level lowers the float lowers so that it no longer blocks off the evap line here and the evaporative vapors can once again get past the check valve into the system now once your vapors get into the system they get to your charcoal canister and this activated charcoal retains those vapors for further use also off of your fuel tank is going to be a fuel pressure sensor actually strike that a fuel tank pressure sensor not a fuel pressure sensor like on the rail and it measures the pressure in the system this is going to be directly connected up to your PCM your PCM is going to measure the pressure this pressure sensor is the critical component that tells whether you have leaks in the system will describe that momentarily now you've got your charcoal canister where your vapors ultimately have entered you will have two exits from the charcoal canister one of them is going to be controlled by the evap vent solenoid this is actually normally open and if you've ever those of you guys with a smoke machine or if you tried the leak test a EVAP system you might mistakenly think you found the problem when smoke billows out of this vent here and that is by design just because the charcoal canister is open to atmosphere it doesn't mean the vapors are escaping so this evap vent solenoid normally is open and the canister is venting but not releasing the fumes your other connection from the EVAP canister goes ultimately to the intake somewhere on there is going to be a little test port a little Schrader valve it's easily identified with a green cap and there's a little Schrader valve in there you can use that for pressure testing smoke testing different things we also have the evap purge solenoid when the evap purge solenoid which is normally closed when that opens and our solenoid turns off and releases this plunger the vapors can now enter the intake and of course you will burn those vapors as I described before if we are not you using the evap vapors then of course the solenoid will activate closing it off the vapors no longer get in there so that's really actually pretty much it that's pretty much the design some of the variances come with the location of these items and they may not have the shutoff valve they may have the shutoff valve for some components but not others so you may see different hosing connections but ultimately this is a setup that you're going to see in most vehicles it'll be very similar one of the main variances though is how the PCM detects faults in whatever the design of the system is and there's two main ways that that happens the way that it happens in this system is done by the fuel tank pressure sensor actually the other one does it too but the opposite and it does it through vacuum so under the right conditions which is going to be during a cold start engine warm up you need to have your intake air temperature sensor and coolant temperature sensor both below I think it's like 86 degrees Fahrenheit or something so it's got to be a cold engine startup and when you do the cold engine startup and these parameters are met and also you don't have other check engine light codes that could interfere with the detection of this things that often would be related to vacuum yeah things like a map sensor or whatever as long as you're all clear on that this is what happens what will happen is the PCM is going to seal the system it's going to close the evap vent solenoids so we are going to close our solenoid with the vent solenoid now closed we are going to prevent the venting from the system and then what it's going to do is briefly it's going to open the purge solenoid now with the purge solenoid open vacuum from the engine is going to draw vacuum on the system so well this is a pressure sensor it's actually going to be looking to measure vacuum once the vacuum is measured by the PCM from the transducer here once that reaches its desired threshold the engine then we'll close the evap perch solenoid and completely seal the system all right now once the system is under vacuum at the right negative pressure that's measured by the PCM from the pressure transducer it looks for a decay in that vacuum and if the decay happens within a certain period of time the PCM is going to determine that the loss of vacuum is either due to a small leak or a large leak if the vacuum is lost relatively quickly obviously a large leak if it's lost over a much longer period of time small leak so that's how the PCM does that now one variance with this system is some cars will actually do the opposite they will have an additional component somewhere in the system usually it's by the EVAP canister and it may even be connected onto the EVAP canister and it is going to be a pump an evap pump now if your system has an evap pump it's still the same theory just in Reverse and what's going to happen the PCM again will seal the system so it's going to close the purge solenoid it's going to close the vent solenoid and it's going to actually we would have of course control of this pump through the PCM and it's going to activate the pump the pump is going to fill the system with air and pressurize the system so instead of vacuum like on most GM systems this would be a pressurized system same thing though the pressure is going to go to a certain point that it's detected by the pressure sensor as the desired pressure point and then the pump will turn off the system remains sealed and again the PCM is going to look at the pressure from the transducer again looking for decay in the pressure if the pressure is lost slowly it will call a slow leak and if the pressure is lost quickly it will cause a fast leak code to set so very simple design I hope that makes sense to you guys now as many of you guys know there can also be individual codes specific not for the leaks but also for the failure of either the purge solenoid or the vent solenoid how would it do that so the way it does that is again very very simple once the system is either under vacuum or pressurized and it passes that decay rate test then it will release the vacuum and what it can do is if it opens the vent solenoid there should be an instantaneous release of the vacuum you the vent solenoid is open when the PCM controls the vent solenoid to open and it notices that there is not a instantaneous change with the vacuum or the pressure it is going to throw a code for a vent solenoid being inoperative also of course the wiring could have the five volt reference signal and things like that that it uses to also test the wire continuity same thing up here if we open up here we should see a rather dramatic change the failure of a change when we open the purge solenoid that would be very indicative that the person oeid is not opening so that is how the evap system works pretty simple straightforward diagnosis and understanding video here the real challenge of course comes when you look at an actual car with these components and how you would actually test them if you don't have a scan tool and also if you don't have a smoke machine so we will do those tests when this car comes in here both with using the scam tool and also if you don't have a scan tool with bi-directional control we'll have to operate these solenoids independently and also do some vacuum tests and things so that's what we'll do on the actual vehicle for the second part of this series and as soon as that car comes in here we'll get started so thanks for watching hope you found this helpful we'll see you on the next part alright guys as promised complete video there I hope you enjoyed it again videos like that will only be available on Schrodinger's Box quantum mechanics with the diagnosis and understanding series like that if your sit in seeing the car here which actually I just fixed with the rich condition we will have that video on rotators box quantum mechanics and you guys who are already members of the channel do me a favor and maybe just drop a little note here for the guys who are still on the fence and just let them know what value you're getting out of the channel and if it's worth three dollars and 49 cents a month I think just this video for this car alone is much less all the other things and final reminder for you guys in the developing countries I need to hear from you put a comment down here or you can also contact by going to the about page and then get the email address and either way you can contact me and let me know which country you're from and if you're eligible I will give you free access to Schrodinger's box quantum mechanics hey thanks for watching I hope you enjoyed the video we'll see you next time

Channel: Schrodingers Box

Views: 133,242

Rating: 4.9103374 out of 5

Keywords: EVAP systems, evap solenoid, evap purge solenoid, evap vent solenoid, evap diagnosis, evap testing, evap canister, evap cannister, P0456, evap large leak, evap small leak, P0455, P0454, P0453, P0452, P0457, P0440, P0441, P0442, P04443, P0444, scannerdanner evap, south main auto evap, eric ther car guy evap

Id: LYifnstYsx4

Length: 18min 22sec (1102 seconds)

Published: Sun Sep 02 2018