How To Perform A Leak Down Test - EricTheCarGuy

greetings to zai eric the car guy here with a 2007 Chevrolet truck with a 5.3 at Ford 5.3 liter Vortech engine in it the person that owns that has told me that a couple of shops have told them that he needs an engine in particular they what's happening with it is it has a misfire as it runs so it doesn't run smoothly and it has a check engine light on with misfire codes and I believe the specific cylinder is number six I thought I might take the opportunity with this vehicle to do our leak down test to determine if indeed it does need an engine because if we find out that it is actually a problem inside the cylinder head that causes a combustion leak if we find a combustion leak we can very easily remove the cylinder head and have that sent out to be repaired as opposed to replacing the entire engine however if we find an issue in the bottom end of the engine that would mean that we might want to consider replacement of the engine the purpose of leak down test of course is to measure the amount of compression that's being lost within a particular cylinder in addition to that it helps you pinpoint where that leak is going and that's what we're going to cover today so I promised you a leak down video got myself a leak down tool got myself a car that could benefit from this test and we're going to get rolling so let's get started and since I got the hood open it won't tell me the miles nice of you oil pressure is good let's pull the pull the code find out what we got here fuel pump primary circuit malfunction interesting cylinder six misfire so you've got a fuel pump code and a cylinder six misfire knew about the cylinder six the fuel pump thing is interesting I wonder if I that was done during some kind of Diagnostics with this you see it moving around in there a little bit of a shake to it your cylinder number six right there let's start with a Power Balance we're going to start by removing the engine cover and if anybody out there GM is listening could you give me a little more room to get up under this hood please are you kidding me yes let's tall people don't like to hit our heads now I'm going to do my power band balance simply by unplugging the coil packs one at a time that is going to be the easiest way rather than trying to remove spark plug wires things like that just connect the primary side of the system very conveniently you have this this is one thing you guys at GM did get right and that was given us shorter valves on the fuel rail and that's good because like it's no secret that you guys have some issues with fuel pumps nothing on six all right I agree that cylinder number six is the issue the next step is I want to verify that number six has spark so I'm going to get out my spark tester and see if it's getting spark as it runs and what I've done is I'm just taking the pigtail off of number six and ran that down to ground so that I can check it spark that there is a good spark all right because I can I'm just going to check it's compression first and then we'll do the leak down so I'm going to remove the spark plug on that one cylinder and disable the fuel and ignition system actually I just need to disable a fuel system disable the fuel system and see what I got easiest way that I can think of to disable a fuel system it's a fuse box give you a explanation of all the stuff there under the cover this one is our fuel pump over here and the way you can read these is lay this out just like this then you can see you got a cluster of relays up here and a cluster of relays up here that look very similar these things are normally laid out in the same way as they are in the fuse box itself so that's how you would read it is you would just sort of try to match up the pictures and since this one right here it says fuel pump and it looks like this one sitting right next to this I'm just going to pull that relay right out of there and turn the key on and listen for the fuel pump and you don't need to start the car just turn the key on and listen you don't hear it buzzing no fuel I'm going to pull that spark plug out do you really need me to show you that I'm going to pull the spark plug out and put my compression tester down on the hole just to get a start just to see if compression or a mechanical issue is at issue here and then we'll bust out the leak down alright here's our plug smells a little oily smells a little like oil or something of that nature even see what I'm doing here yeah smells like oil before I go busting out my leak down I'm actually going to do a quick compression test to see if there's an issue in the cylinder so if there is if the compression is considerably down in this cylinder then I'm going to know that and if I do find that it's significantly down the next step is to get it up the top dead center and do the leak down so start with a quick compression test it's important to open the throttle whenever you do a compression test in the last compression test video I put the foot to the floor to disable the fuel system and it open the throttle at the same time I thought it was pretty efficient to do it that way this one I've got the fuel pump disconnected also so it really doesn't matter as far as fuel cutting with me pushing on the gas pedal but I need to push on the gas pedal this time in order to open the throttle while doing the compression test hey that's not very good at all we have no compression in the cylinder now it's time to find out why we need to get the cylinder up to top dead center we need to figure out if it's on the exhaust or the compression stroke now a good way to figure out if cylinder is coming up on a compression stroke at least one way that I know is I take a small piece of paper or a piece of tissue or something really light stuff it in the cylinder hole and as I spin the engine around the theory is is as the piston is coming up on its compression stroke it will blow that little piece of paper or whatever you got in there out of the hole on its way up and then I stick a screwdriver in there and turn the engine over by hand very slowly until I see it reach its apex and once it's done that I know it's a top dead center and that's when I can perform my leak down I'm going to use a small piece of TP in the hole TP for my bunghole oh and just sort of stick it down in the spark plug hole I'm really just going to focus on cylinder number six here because I the rest of the cylinders seem good the problem cylinder is definitely number six we learned that through the power balance we learned that through the compression that it has no compression and actually I have my doubts as to whether or not this tissue is going to blow out because there is no compression so I'm going to be hard-pressed to try to figure out using this method whether or not I'm a top dead center on the cylinder the other thing I could do is go through the firing order starting with the cylinder before this we have to find out the firing order on this on this engine but if I can find out the cylinder that fires before number six then what I can do is take that spark plug out and verify that that's coming up on its compression stroke once I know that I know six is going to be next and I can determine that number six will be a top dead center on its compression stroke and we would be able to do our leak down from there leak down is different from a compression test in that you can actually tell where the leakage is with a compression test it just tells you that there is a leak it doesn't say anything about where however a leak down test will not only tell you give you a good indication of where the leak is coming from it will also give you an idea of how big the leak is that's why it's called a leak down let's look at that tool real quick okay this is your leak down tester shop air gets connected here this is the air regulator it's tools are brand new actually went out and got it for you e okay and this is the regulator that I may have to get some kind of tool to get this to come loose but this this regulates these gauges here and this this tells you the amount of leakage and this is the pressure going in so basically what you're doing is you're calibrating this to your shop air pressure when you hook it up and this hooks up to the exact same lead as your compression tester so this is the part that's in the cylinder that would be normally with a compression tester I'm not going to use this one though and I'll tell you why later in the video but you can't use a hose for a compression tester for this test unless you modify it which I'll show you later but anyway the idea behind this is you run compressed air into the cylinder that you know has a leak or suspect has a leak or you're just trying to check the general health of your engine unlike a compression test this will tell you the amount of leakage that you have and generally the rule is if it's more than 20 percent it's between cylinders it's excessive actually if it's more than 10 percent it's kind of excessive so you want you want all the cylinders of an engine to be within 10 percent of one another so you don't want one to be hugely leaking because if it does you'll have what you have here which would be an engine miss but the way you actually pinpoint where the leak is going that is the fun part so I'm going to see if I can figure out getting this thing up to top dead center on the cylinder you're testing so for a leak down unlike compression testing where you can turning can go leak down you have to have the cylinder top dead center all the way up the top of its travel on the compression stroke the exhaust valve cannot be open both valves have to be closed so compression stroke top dead center in order to do the test that's the first thing you need to do ever have those dumb moments well I just figured out that this thing won't turn unless you pull it out and then you push it in to lock it yeah so grab it a tool try to twist this pop it out and turn it if it's not turning right away okay all right well they did do this right man I got all kinds of room to get down in here to get on this crank pole this is what I'm going to use to turn this engine over by hand and I'm just going to go on a limb traditionally these engines train in a clock turn in a clockwise direction so spin it in a clockwise direction there it is move just a little bit now that I know that I want to remove the tissue and insert a screwdriver or equivalent or something so that I can monitor the piston as it comes up all right so I'm going to turn it sneak this screwdriver down into the cylinder her while I turn the crankshaft over let's see if I can feel the top of the piston as it's coming up I'm hoping I'm gonna feel the top of the piston so coming up that's pushing my screwdriver out and when it stops it starts to recede again that's when the Pistons reach the top of its travel I'm pretty sure that that's top dead center on that piston take your ratchet off the crankshaft you run pressure into the cylinder sometimes the engine will rotate over sometimes under its own compression so you want to make sure you take your ratchets and stuff off of there and set those aside what I'm going to do now is I'm going to insert the same thing that's similar to the compression tester tester but it's for the leak down so I'm going to get that down inside the cylinder so I can run my compressed air there before I thread my hose down in there I just put a little bit of oil on these threads and on this o-ring just a little bit not a lot this will help it go in easier because normally what you're doing is you're getting this lined up inside the hole and then you're twisting it like this so that's that's how you normally you normally do your twisting back here and you just use the other end to guide until you catch the threads so be careful not to cross thread it while you're trying to get it down in there you don't want to get it down in there so tight let you end up losing your tester just get it down far enough to where you know the o-ring seats so it seals up the cylinder and that's it so when it stops turning and it's in there you're in there alright before we put this on the truck you're going to hook it up shop air make sure that this valve is turned all the way counterclockwise first because we need to calibrate it before it goes on the car now we're going to turn it in memory pull down on it on this particular one I'm going to keep turning it in till this gauge reads zero and now we're going to lock it down so going farther I'm gonna say that okay these can be at least this one's a little tricky some of these are better than others there we go so I'm going to lock that off so that's the reason why we have this lock-in thing here so now I've got it locked off I know that's not exactly on zero but it you know what this this is not going to be 100% exact but as long as you're in that yellow calibration zone you're good and now we're going to go take this in and hook it up to our cylinder okay you see that went straight to 100% so it's leaking out 100% now we need to figure out where what you need to do next is you need to listen in all the different places that's gone down a hundred percent you need to listen to all the different places where air could be escaping and it's quiet in the shop and I don't know if this testers a little weird or what but yeah it does say that it's 100 percent leakage but I don't hear it going anywhere normally hear it but if you suspect that it's leaking past the rings into the crankcase well that's not a good sign suspect that it's leaking past the rings into the crankcase you listen here for hissing noise the air escaping if you suspect that it's leaking into the coolant and you might have a head gasket problem it will make bubbles in here you can't really get into the top of the radiator on this one but UNC and here bubbles if you've got an intake valve that's leaking I'm going to remove the snorkel here and if there was an intake valve leaking you could open up the intake and you hear the air rushing out in the intake it was leaking out of the exhaust an exhaust valve was bad you can go back here to the tailpipe and listen and hear it rushing out here what concerns me is I don't hear it going anywhere okay I'll admit it it's a cheap leak down tester you know I don't often do these tests and I don't really feel like spending a great deal of money on one of these testers but it's nice to know where the leakage is going if you have leakage well I got another solution for you all right I'm not having faith in my tester because normally when I hook these things up and there's a hundred percent leakage I hear it hissing and going somewhere not sure what I'm doing wrong but this is the way I've done it long before I had one of those testers that is actually how you use the tester in it and it should work but I just take my hose for my compression tester take the end off if you look down in there there's your Schrader valve like on a tire take that Schrader valve out now mine for whatever reason no longer comes out but if you take that Schrader valve out and just hook this up like you're doing a compression test into the cylinder and then just chuck it straight up to the air without the Schrader valve in this this would be spraying all over the place you chuck the air straight up to the hose you can hear where the air is coming out and you'll be able to find a leak of where it's going so a leak down tester will tell you the percentage of leakage and give you you know like say if you've got an engine that's marginal that you know it's pretty worn out and you're trying to figure out whether it's time for rebuild something along that line and you need to know a percentage you need a number leak down tester if you need to know where the leak is just take a compression tester take the Schrader valve out shove it down the cylinder like you're doing a compression test hook it up the shop air listen at the tailpipe for an exhaust valve leak listen at the intake for an intake valve leak listen at the cooling system or take the cap off the radiator look for bubbles for leak into the into the combustion chamber and if it's a leak past the rings down into the crankcase take the oil cap off of the dipstick out and you'll be able to hear the air rushing out of that place cleanest day and sometimes you'll even be able to put your hand over those things and you'll feel it blowing against your hand so this this helps you pinpoint like a compression test the compression test just gives you a general overall this leak down helps you pinpoint where the issue is exhaust valve intake valve coolant leak compression leak into the crankcase that's that's why this test is different so I'm going to just take the shop air and run it straight into the cylinder see what happens maybe this one has a Schrader valve in it no no now I'm hearing something won't you listen plug off the wind and hear it coming out of there that's where the oil cap goes no bubbles down on the coolant don't hear anything out the tailpipe I don't hear anything in here that's the throttle plate there it is compressed air go and stir it into the cylinder you know you're always going to hear a little bit coming out of here this is a bit and since the seller has no compression I believe number six then if I'm to guess I think it's got broken rings yeah if I'm going to guess on this one I'm going to say broken rings now just for the heck of it I'm going to test the cylinder next to it just to make sure that maybe that one's sealed up or the next cylinder in the firing order just to make sure that my testing methods are sound this is my first time using this particular leak down tester I don't really trust it because I didn't hear that air rushing out like I did when I hooked the air straight up to it it just showed me that it was 100% leakage and then quit I'm not exactly sure why that is perhaps that's the way it's designed but most of the leak downs that I've used what it shows you the percentage of leakage and you can hear the air coming out just like I'm hearing it on this one so I'm a little confused as to why it's acting this way so I'm going to verify my results by testing a known good cylinder to see how it reacts and if it reacts normally and there is not a whole lot of air that appears to be rushing out of the oil cap then I'm going to click conclude that yes this cylinder is having a leakage problem and it is in the bottom of the engine not the top end of the engine this test is good if you're worried about a burned-out valve cut being a cause of a loss of compression if that was the case you'd have to do is remove the cylinder head and send it to a machine shop or whatever replace the valve to reseal the cylinder head in the combustion chamber up there but a leak down at the bottom in through broken rings whatever that is going to be a different animal indeed so we may be looking at replacing the engine in this truck but at least we have evidence and we know we don't guess we gather evidence and we base our conclusions on our evidence we don't go by guessing all right so just to verify that my tester is working correctly I decided to move to a different cylinder to see if I could get a more a better result and pulling this spark plug out found evidence of burning oil you see this on a spark plug and this was number one cylinder you know that the engines consuming oil so I'm curious to see what the leakage is on this particular cylinder let's find out this is number one cylinder so I know my gauge is accurate because this one says it has moderate leakage as whoops as opposed to the other one I had a lot of leakage so I guess I guess that is it I guess that one over there it's got 100% leakage you got some kind of ring problem we saw the kind of oil that was burning in this one I'm just surprised that I don't hear the air rushing out like I normally would I'm going to go check the oil cap now but this is what you're looking for you're looking for it to be in the green fairly simply and you're looking for no more difference between cylinders then let's say 10% 15 yeah maybe okay but if if they vary more than 10% per cylinder and he got one that's like way down like I got over there like that hundred percent well yeah problem this time I do hear a lot more at the oil cap so I know the engine is leaking internally orange might look good on the outside but on the inside it's not looking so good in fact I don't have to go any further with any more cylinders I mean we got one with a hundred percent leakage and another with sixty percent leakage so that says inside that engine doesn't look so good so it's got to come out be replaced rebuilt whatever cylinder leakage techs testing Diagnostics that will save you a lot of trouble if I'd have found that one of these valves was bad like maybe it had a burned up exhaust valve that wasn't sealant or something like that could have easily found it with a leak down test and then I would have only had to remove a cylinder head instead of the whole engine think about it take some time figure it out don't shotgun i'm eric the car guy i hope this video was helpful to you and gave you some useful information you can always visit me at eric the car guy come you can also follow me on Facebook and Twitter and on Sundays most Sundays I do a podcast at 12 p.m. Eastern Standard Time so if you want to check that out and listen or if you want to listen to past podcast or miss the ones that have already happened go to the player on my homepage scroll down to the bottom click on that player and that will lead you to places where you can find all the old episodes which are also posted on iTunes under car and truck talk comm thank you very much for watching and as always stay dirty

Channel: EricTheCarGuy

Views: 1,005,191

Rating: 4.8654184 out of 5

Keywords: engine, leak down, leak down testing, engine leak down test, engine leak test, diagnostics, automotive diagnostics, auto repair, car diagnostics, how to diagnose car problems, engine miss, misfire, misfire fix, misfire cause, GM, Tahoe, 5.3L engine, performance problems, 5.3L diagnosis, spark, fuel, eric the car guy, ericthecarguy, etcg, etcg1

Id: WgrfT0LFMhc

Length: 27min 34sec (1654 seconds)

Published: Sun Feb 06 2011