Engine Mechanical Testing with John Thornton

hello this is Bob pipe from automotive seminars and welcome to this free introduction to our first online training event titled engine mechanical testing within cylinder pressure transducers presented by John Thornton today we will be introducing the topic along with our in cylinder procedure TDC versus spark plug firing and cranking compression testing this class will have three more parts that will be broadcast separately as live events for more information on those please check out our web site automotive seminars dot-com here is John Thornton hello my name is John Thornton and on behalf of automotive seminars we’d like to welcome you to this training program in solar pressure transducer Diagnostics you know for many many years in this industry we have relied upon a mechanical compression gauge to help us determine the ability of a cylinder to breathe and to build pressure and of course as time has gone on we have seen a change in how we diagnose engines and the equipment we use to diagnose engines and certainly insulin or pressure transducers really dramatically helped us analyze engine problems now for those you that are currently using an insulin or pressure transducer you’re well aware of the many benefits but for those of you watching this program who have not had an opportunity to use a pressure transducer you might be wondering is it really worthwhile to switch from my mechanical compression gauge that’s been so reliable to this other method of testing and I would say that the answer is yes it is worthwhile let me share with you just some of the benefits with an insulin or pressure transducer you can measure the actual cranking and running compression pressures now that’s not to say that your gauge is inaccurate but more along these lines let’s say that we have an exhaust path restriction in a cylinder and then when a piston comes up on an exhaust stroke instead of having about zero psi on that straw it’s got 5 10 15 maybe even 20 psi so if I’m using a compression gauge and I’m cranking or running that particular cylinder I will never see that the Schrader valve in the hose or in the gauge will trap the highest compression so if the highest compression was 150 psi on that compression stroke we will not see anything less than that but a insulin or transducer will show us the actual pressures in all four strokes also we can determine valve opening and closing events now of course in the four-stroke cycle we have four valve events the insulin or pressure transducer allows us to very accurately measure two of those when the exhaust valve opens and when the intake valve closes and I’ll explain as we progress why the other two are far more difficult to measure also the pressure transducer helps us determine how well an engine breathes how well we get air into and out of that sooner let me give you an another example let’s say that I have an intake valve for whatever reason does not open fully so there’s some type of intake path restriction and depending on the condition in which we’re testing the engine a gauge may not show that but if I’m using an insulin or pressure transducer and I have an intake path restriction I will see deeper than normal vacuum on the intake stroke so when I say the intake stroke I’m not talking about the vacuum in the intake manifold I’m talking about that vacuum in the cylinder so instead of seeing I’m at a normal 18 19 20 21 inches on my C as deep as 25 or 26 inches and that would help identify what’s wrong with that particular cylinder so that that’s a real benefit and I finally in this discussion anyway we can determine with a high level of accuracy when the spark plug fires so if I wanted to determine if the plug is firing you know at TDC or slightly before TDC going in solder is a pretty quick way to do that now if it’s not firing at the right time my transducer might help me identify is there a crank reluctor issue so whether the reluctor is mounted on a harmonic answer the crankshaft or a flywheel we can determine if that reluctor is shifted one way or the other so these are just some of the benefits and as you watch the program you’ll see there’s a lot more to come so for this session we have a number of topics that we are going to cover we’re going to start out with an insulin or procedure just a very brief couple things to keep in mind discussion there we’re going to take a look at plug firing which I’ve titled insulin or TDC versus plug firing then we’ll look at cranking compression

testing now cranking compression testing you know it’s pretty basic we’ve been using gages for years to do this but we use an insulin or pressure transducer there are three points that I’m going to focus on specifically for insulin then we’ll take a look at our analysis stage and I’ve broken up the analysis into two categories just making simple pressure measurements and use of overlays and then the second part will be the in depth analysis of the actual pattern where we’ll look at the four-strokes expansion exhaust intake in compression after we go through this which I hope will lay the foundation for Diagnostics we’ll move to problems and while there are many types of engine mechanical problems that we can encounter I’ve looked at what I consider to be the four most popular by category so we’re gonna look at exhaust path restrictions cam timing errors valve sealing issues and finally we’ll wrap up with intake path restrictions so kind of the summarize I’m gonna lay the foundation first from an analysis viewpoint then we’re going to take that information and we’re going to apply to a variety of problems so we’ll come on aboard our first topic is what I would call insulin or procedure and depending on how you acquire your tooling if you buy a kit from you know Pico for example or from automotive test solutions for example you will get the transducer in the hoses and there will be no Schrader valves if you decide to assemble a kit you know build your own so to speak please make sure that you remove the straighter vowel so we don’t we don’t want pressure being trapped in a hose or in the transducer so no Schrader valves also it’s a good idea to disable fuel for most of our testing so if we’re cranking engine over usually we want to have some type of ignition event for reference in order to measure timing so and if we’re if the engine is running of course we want to keep spark but we wanted sable fuel for that particular cylinder now that’s easier said than done you know if you’re working on a four cylinder where the injectors are right in front of you it’s fairly easy to disconnect an injector but if you’re working on a late model with you know gasoline direct injection and we can’t even visually see the injectors we’re not going to be able to disconnect an injector now we might be able to use a scan tool to disable fuel temporarily so if you can’t disable fuel while it’s running you know it’s just something it can’t be done so we let the we let the cylinder fuel just keep in mind that there is fuel getting into the cylinder also pretty important but all challenge as well is it’s always advisable to acquire cranking compression specifications before I actually do a cranking compression test and the same with valve timing specifications I’d like to know when valves are supposed to open and close now sometimes manufacturers will give us that information and sometimes they won’t and if it’s absolutely necessary for our diagnosis we may need to find a known good vehicle with a similar engine to pull that information from but that that is very helpful and finally I would say you know whatever you have whatever you buy it’s it’s expensive so you want to protect your investment I want to show you three pictures of what I mean by protecting your investment now this is an example of a pressure transducer being used on a GM 4200 and it’s a fairly straightforward process the coil the spark plug have been removed the hose has been threaded into the cylinder and the transducer has been connected to the hose now in this example the transducer literally stands on the hose it’s rigid enough that it’s safe so I can create this engine over I can run this engine I’m not really worried the transducer here’s a Chevy 3.9 v6 where the connections are similar however you’ll notice that I’ve got rags underneath the transducer a top of the conduit so I don’t like to lay that pressure transducer on anything I always want to kind of cushion it so whether it be rags or some type of foam you know this is a an expensive device and I do not want to damage it nor do I want to affect its accuracy and finally this is a Chevrolet v8 and you can see I’ve got the pressure transducer supported by a bungee cord and I’m pretty serious when I tell you that do not let these transducers whether it be pressure or vacuum transducers you know bounce around and ending it’s metal or plastic or the manifold it’s not good for the transducer and ultimately could affect the life of the transducer so always protect that investment our starting point from a diagnostic viewpoint is going to be insulin or top dead center versus plug firing now I could have

titled this checking ignition timing and this is a pretty good way to get started with using an insulin or pressure transducer because it’s fairly straightforward and it provides all valuable information very quickly so my goal here is I want to go in cylinder and I want to compare that pattern and specifically my top dead center point to one a spark plug fires now dependent on the ignition system that you have on a vehicle that you’re working on we have a variety of choices to acquire an ignition pattern you know if the vehicle has plug wires we could use a capacitive pickup and get a secondary voltage pattern we can get a primary voltage pattern so if you have access to the negative side or the PCM side of the coil like a Chrysler two wire coil or an older for two wire coil primary voltage is fairly easy to get primary current is also a good choice and if you have the module inside of the ignition coil the trigger signal that the PCM sends to that module within the coil is also a good source and finally if you’re still working on vehicles that have plug wires like I am a sink probe sometimes called an inductive rpm pickup are also quite useful so this particular probe is not capacitive its inductive so when I clamp it around a plug wire it senses the high voltage secondary current flowing through the wire and it induces a voltage back to my scope that I have a signal on so that is also quite valuable so there’s a variety of ways to acquire ignition so again a pretty would good way to get started with a insulin or pattern is to find top dead center it’s a pretty straightforward process so as you look at this you can see as if you follow my mouse here the piston is coming up on compression so we are building pressure rapidly there the pressure is peaked and now the piston is changing direction and it’s being dragged down the cylinder by the crankshaft and we are rapidly dropping pressure so this point right here is commonly called top dead center now I’d like you to please note you know the goal of course of any training program including this training program is to provide accurate useful information so I don’t really want to say that it’s true top dead center the words that I’d like to use to describe this have always been it’s a reasonably accurate top dead center so I will say that again it’s a reasonably accurate top dead center it is not a dial indicator top dead center let me give you an example what at what I mean if you if you watch my arm for a moment and pretend that my forearm is a ride and my fist is the piston and we’re stroking the cylinder so the only piston comes up on compression it reaches top dead center and of course the rod has to swing before the piston starts to move down so the amount of time that the piston is at top dead center in which the rod must swing is called piston dwell and that occurs for a very short period of time but nonetheless it occurs so we are in in cylinder we’re not actually looking at the physical position of the piston we’re looking at that pressure because of the position of the piston so is a pretty close approximation at the top dead center but always keep in mind it may not be perfect but it’s reasonably accurate so with that that’s the term that I’m going to use so the best way to get started with this check is to find a known good vehicle so I have a 2014 Taurus with a 3.5 now it happens to be a twin turbo EcoBoost Taurus SHO but regardless it’s going to provide a good example so this is a known good so cylinder 4 in the front is accessed the coil and plug had been removed and the pressure transducer has been installed and the engine starts and run so now we have a running compression pattern and again my goal is to determine where the plug fires so once I have my running compression pattern I’m going to access the negative side of the coil so what while you can’t see this the coil is still connected and there is a spark tester connected to the coil so I can get a primary voltage pattern so in blue is the primary voltage pattern so as we look at the big picture when I say the big picture I kind of step back and we have the four stroke cycle plus a little bit more on the screen but you can see our reasonably accurate top dead center twice and you can see the plug firing via the primary voltage twice as well so I am going to zoom in and recenter and right now I can I can clearly see that the plug via the primary voltage is firing to the left of top dead center so as you can see where the cursor the mouse is hovering right here that’s my reasonably accurate top

dead center so that’s my reference so when we’re using a lab scope and we see something that occurs to the left of whatever your references in this case is my reasonably accurate top dead center we say that that event is advanced relative to that point if it occurs to the right we say that event is [ __ ] relative to that point so I follow what I call the double our rule if something is to the right of where it’s supposed to be relative to my reasonably accurate top dead center it is [ __ ] I don’t have a rule for the advanced side but it’s the other so right now I can tell you that my plug frying looks pretty good now I can measure this very accurately with a cursor but it’s not necessary at this point but it is important to be aware that while most manufacturers no longer publish when a spark plug fires plugs still fire in the vicinity of where they used to be years ago so if you think back in the old days for example working on a Ford you would pull the spout connector to set and/or check ignition timing we might have numbers like 10 degrees before top dead center and other manufacturers might use numbers like 0 4 6 8 12 14 so we have a sense for it normal is so I expect when I go in cylinder and I’m checking ignition timing I expect it to be at about top dead center and or 2 left maybe up to 20 degrees you know depending on the condition of the engine what’s going on with the engine but I expect to see it to be to the left or to be advanced let’s take a look at a problem vehicle so this is a Ford product as well that’s at a body shop there was a pretty severe collision are the engine was removed to do some frame straightening now the engines been put back in and unfortunately it does not start so here are the details this is a 2014 Ford Fiesta with a 1.6 liter and the issue is curly the engine cranks strongly but it does not start and I was told some information about the vehicle that it cranks well that it has compression and it has spark so I’m going to do some analysis here without supporting backup so as we progress in the training program I will show scan data to tell you how I got to where I got but for right now my goal is just to perform this test just to check ignition timing so this particular Ford uses a three wire ignition coil instead of a 2 wire ignition coil which tells us that the module is actually inside of the coil so as we take a look at a wiring diagram we can see that the on the left is the PCM and there’s a white with a violent wire that goes from the PCM to the number one coil on plug coil with it’s and kernel module that’s our trigger signal so this is a 0 to 5 volt trigger signal that the PCM sends to the module within the coil to fire to plug so that’s going to be our reference that’s what we are going to measure now when I do this I am going to disconnect this coil I’ll explain in just a moment so as you look at the picture you can see the pressure transducer is connected to the cylinder and you can see my blue scope lead connected to my probe which is then connected of course to the coil connector but there’s no coil the coil has been removed and I’ve removed the coil to minimize an issue and the issue I’m concerned about is if I put a spark tester in the coil which of course can be done and that spark tester was to somehow lose its ground that high voltage current might look for another path to ground and that other path could be my transducer so when I have ignition systems that are designed like this I will remove the coil however with a coil removed there is no loading effect on the trigger signal so the trigger signal is going to look a little bit differently open circuited versus the loaded circuit with the module and connected but that’s ok because it’ll still provide me the same correct information so the engine is cranked over red is in cylinder blue is the trigger signal open circuited because the coil is not shown and I’ve added some overlays to better define the pattern but over here on your left where the mouse is hovering that’s my reasonably accurate top dead center for that cylinder in blue is where the plug is firing and you can see that immediately is to the right so right away we know the ignition timing is [ __ ] and I’ve grabbed a second curser and I’ve made a measurement now because this pattern looks a little bit different because it’s unloaded I am actually measuring on what I would call the leading edge of the signal and the plug would normally fire on the trailing edge but it’s not going to make that much difference in this analysis so my cursor right here again where the mouse is hovering is approximately 7

four degrees after top dead center and it’s actually just a little bit more but I’ve measured at that point so the plug is firing 74 degrees after top dead center so the piston is almost halfway down at that point there’s no chance for combustion you know there’s hardly any pressure in the solar at that point in time and while there may be spark and while there may be fuel there’s no heat from compression so there’s no way we could have combustion and there’s no way the engine could ever start so very quickly we’ve identified the core issue is that the ignition timing is severely severely [ __ ] and normally when dealing with these situations you ask yourself what determines when a plug fires and generally the answer is well the crank sensor signal and its relationship to the crank so I don’t believe I have a bad crank sensor but my next question B is well where is the reluctor that drives the crank sensor and I would take a very close look at the reluctor and in this case we would find that the reluctor is in the wrong position now let me show you a couple pictures of what I mean when I talk about the reluctor is in the wrong position this picture is from another Ford it’s not from this particular our Fiesta with a16 this is from a 2010 Ford Fusion there was also a body shop vehicle that was hit very very hard and the engine would not start now what you’re looking at is the backside of the harmonic balancer from this 2.5 liter let me make the picture just a little bit bigger and I want you to notice two things the hub has an alignment hole right here so when you normally install this there is a bolt stud that can be used to align the balancer to the right position on the timing cover so that is part of the the hub now this is our outer ring with our reluctor teeth and Ford uses a thirty 6-1 reluctor teeth so this 36 tooth reluctor room for 36 one’s missing 35 but there’s 36 minus 1/2 provides the ignition trigger for out a PCM this is the balancer that came off the engine that would not start my next picture is the balancer that went back on the engine that allows it to start please notice the difference and the difference is is the relationship between the alignment pin on the reluctor versus the alignment pin on the hub you’ll notice that position and this of course is for manufacturing if I go back this is the bad one so the outer reluctor the outer ring is shifted on the inner hub causing the ignition timing to be severely off and believe it or not these are the types of problems that you run into it’s kind of an unusual problem this was due to the impact of the front end collision that caused this to shift but if also if you look within the the bore you’ll notice there’s no key way so the location of how that balancer is installed is equally important give you one more example this is a crankshaft from a GM 3.6 liter and we’re looking at you know the back end of the crank where they have their 58 tooth reluctor pressed on the back of the crane now this is a reluctor in which there’s room for 60 teeth but two are missing so it’s called a 58 tooth reluctor now the crankshaft on your right has the problem the reluctor has actually shifted its position so if you notice where the two missing teeth are right here relative to the to the throw so you can kind of see the machined area and there’s the cast line right there so we kind of notice that it’s about one tooth to the right if you come over here to the new crankshaft there’s a two missing teeth there’s our throne right there is the machine to cast surface so that’s one two three almost four three to four teeth so you can see that the reluctor is shifted in both of these examples the fusion and it’s three six that was identified by comparing when the plug fires to a reasonably accurate top that Center so these are just a couple of examples of what a technician might find when that ignition timing is incorrect and of course this will also affect how we look at cam timing via our cam sensors as well of course before I leave this topic there’s something else to be aware of you know for many many many years plugs fired at about top dead center or before top dead center and if you gave them our p.m. with a lighter load you know they would advance well of course as technology marches on we see things that change so of course today we have many many vehicles that have gasoline

direct injection and GDI breezes own set of strategies with it so what we are looking at right now is a picture from an SAE paper and in the upper right hand corner you can see the number of the SAE paper and the title was bosch motronic M II D and was for wooden four at the time the new GM 3.6 liter with gasoline direct injection and in this paper they talk about many strategies but one of the strategies they talk about is a catalyst heating strategy and this occurs typically on a cold start transmission still in part and during this catalyst heating strategy the PCM is trying to get the catalyst up to temperature very quickly so it does a number of things one of the things that it does it will [ __ ] the ignition timing and as its retarding the ignition timing it will open the throttle blade further to allow more air to enter into the engine it will also fire the GDI injectors twice in the four-stroke cycle what I’m interested in is the ignition timing component of this so you can see from the illustration and are you in gray represents a GM 58 tooth reluctor that we just talked about for example and at the top here is top dead center and to the left as you look at this is normal timing advance however where it says catalyst heating you actually see it’s on the [ __ ] side and I’ve seen these numbers you know is [ __ ] this 20 degrees so what I’m getting at is if you are checking ignition timing on a cold engine that has gasoline direct injection and the ignition timing is [ __ ] 5 10 15 degrees that might be strategy and it may not be broke and we always have to weigh what we are measuring with the issue if an engine doesn’t start have an ignition timing being [ __ ] 10 degrees is not the reason you know 74 degrees like in my previous example that’d be a pretty good reason but clearly not a 5 10 or 15 degrees but we need to be aware of strategies like this that helps us kind of keep us on track to make sure we’re not chasing something that’s actually good and not a problem so our next area we’re gonna look at is cranking compression testing and once again the gauge has served as well but you’ll see in this section particularly like in the last section where we looked at ignition timing how the transducer really provides useful information so there are three primary points that I want to make in this discussion I’m going to tell you what they are now I’m going to explain them and I will summarize them at the end of this particular topic number one is I would like to pull a spec for cranking compression testing I realized many manufacturers don’t produce a spec I understand that but if you can get one let’s try to get one number two as you do your cranking compression test always depress the accelerator pedal push the pedal to the floor now in the old days when we had linkage we were guaranteed at that throttle blade opened of course many many vehicles that we work on tell us electronic throttle control and there’s absolutely no guarantee then you push the accelerator pedal to the floor that the throttle blade opens all the way it may not open at all it may open a part of the way or it may open all the way I don’t know but my technique my approach has to be consistent but I will show you the importance of having a throttle blade open and third which will be best illustrated when I actually show you some patterns but third is that when you’re using an insulin or pressure transducer and you crank the engine over I expect all of my pressure pulses my compression stroke pressure pulses to be about the same so if I were to measure pressure pulsations and the first one was 150 150 150 150 I’d expect that when I was finished cranking after maybe one or two three four or five seconds that I would have almost could put a horizontal line across those pressure piece and I will show you that with an example so let’s start out by looking at this 4200 and this is a cranking test of this 4200 in a particular sonar now you’ll notice the scales first over here on the lower left that’s my zero and you’ll see there’s one volt there’s two volt so on this particular setup with this scope and this transducer for every one volt that I see that represents a hundred psi and I’ll talk more about that as we progressed so two volts would be two hundred psi and 1.5 is 150 psi so I ran a horizontal cursor across the peaks and I’m at about 146 psi 1.46 bolts now you’ll notice that my very first pressure pulse is higher than the rest

and that’s not unusual to see and the reason for that and a reason that I don’t pay that much concern to it is that when you first start cranking an engine over we really don’t know where the piston is in the cylinder it could be a bottom dead center it could be halfway up it could almost be to the top I don’t really know where it is but I know with this subsequent cranking that I will go through the entire four stroke event so the first one I always observe but I don’t expect it necessarily to be the same as the following pressure pulses so my following pressure pulses are 146 psi so my question is is this good is cranking compression on a 4200 of about 150 psi is that a good number and depending on our backgrounds we may be able to answer that with a yes that’s a good number or we might answer with a No however it’s best to keep opinion out of this if we can so I’m gonna see if I can look it up and you can see that we’re on the GM website I’ve identified in the upper left-hand corner it’s a 2005 Trailblazer and I’m looking at my mechanical specifications and you can see it’s a 4.2 litre of course and I go down to the lower area where I’ve got a yellow highlights as engine compression tests 215 psi so the GM specification for this particular engine is 215 psi so if I come back and I ask the question again if 215 psi is the spec and we’re reading 150 is that any good and of course the answer is it’s no good it’s a failure and what you don’t know from this pattern it’s a little hard to tell from this pattern by itself is that this particular cylinder has a leaking valve now I could never tell you which valve it is by this particular information alone but my point is that once upon a time 150 psi was considered to be good compression on many any engines I don’t want agree I don’t want to go by once upon a time to the best of my ability I’m gonna pull a spec and if I can’t pull a spec I may have to find a known good vehicle I may have to do a little bit of research speaking of research let’s take a look at an engine that GM introduced in the 2014 model year the 2.5 liter this is a four-cylinder engine now the reason I’m interested in this particular engine it has variable valve lift on the intake so it’s kind of a newer technology that we have not seen before and the GM four-cylinder engines and I listed that it can be found on a Malibu or an Impala and has a VIN L so here’s a picture of the engine shown from the back side of the engine and if you look towards the top where the cam cover is you’ll notice that there looks like there’s two solenoids with a connector and it’s it’s actually one solenoid body but it’s got two separate solenoids in there and that’s the variable valve lift solenoid so this particular engine does have variable valve lift and as I look at these specifications for this engine I notice that the compression ratio is high it’s eleven point two to one now unfortunately they don’t publish cranking compression so I don’t know what the compression is supposed to be in case one day I run across a bad one but my sense is that if that ratio is that high while the compression must be pretty high don’t they go hand in hand so I thought the best way to find out would be to actually do a compression test on a known good 2.5 so I acquire a 2.5 liter and you can see the setup the pressure transducer is in cylinder number 2 and I am preparing to crank the engine over so I’m using a Pico transducer and I don’t have to protect it it stands up straight by itself and I crank the engine over and I please notice my observation here that the accelerator pedal is to the floor and I crank the engine over so in this example my first compression pulse all the way in your left is equal to all my other compression pulses except for the very end when I with a cranking stopped and I put a cursor across and my scale is still the same every one volt on the left is 100 psi so my cursor is about 2.8 1 9 volts so it’s about 280 psi I want you to think about that for a moment this is a gasoline engine cranking over that has good compression ratio that produces 280 PS I imagine I did not have known good and one day I work on one of these engines that has some type of valve sealing issue and I see 210 or 220 psi which by most standards is really good but it’s not so good if 280 is the norm that’s why it’s so important to have specifications

either we use what the manufacturers provided for us or we spend the time when we get them ourselves let me give you one more we have heard a lot about Mazda’s SKYACTIV you know is this impressive technology that they have and they have it for both gas and diesel engines and I’m interested specifically in the 2.5 liter gas engine found in North America so just a couple of highlights that we are told that this particular engine is a 13 to one compression ratio which is really amazing you know the 2.5 that we just looked at had really good compression ratio but this is higher and the intake cam has a wide phase angle of 70 degrees so it’s very aggressive in its ability to move that intake camshaft around this is a spec sheaf for the skyactiv-g engine and certainly I’m not going to read all of this to you but I just want to note here at the top bullets that rest of world the compression ratio is 14 to 1 but here in North America at least now for 2014 we have 13 to 1 so that’s the vehicle that we’re going to look at it has a 13 to 1 compression ratio we’re going to service information to look up the compression pressure and we actually have compression pressure so towards the bottom where you see my black arrow this is again at SKYACTIV 2.5 liter I go to the right the standard compression is a hundred and thirty-eight psi at 300 rpm now I almost wonder if that’s even accurate because a moment ago with a 2.5 liter we have 280 psi with eleven point two to one now we have a similar engine 2.5 liter with a much higher compression ratio and they’re telling me that the cranking compression is only 138 psi something just seems off about that but is you know the only way to figure this out is to go check so a cranking compression test is done and you can see on the left the initial pulse was a little bit higher than the others however the other pressure pulses are all pretty much the same which is to be expected and the cursors put across and it’s one point three two volts and still every one volt is 100 psi so it’s 132 psi so this engine measured in that cylinder 132 psi which is pretty darn close to the spec of 138 so it turns out that that must be okay but it’s really surprising given the fact that the compression ratio is so high but there’s always more to the story the compression was also checked on this engine on a cold start not cranking but running on a cold start and the reason for that is this is a gasoline direct-injected vehicle as well that also employs that catalyst heating strategy we talked about a few minutes ago and during the strategy the ignition timing is [ __ ] but the throttle blade is opened and the intake cam is phased so right now we’re catching part of this part of this start and you can see over here the scale is exceeding three volts and we’re still at one volt is 100 psi so I’m going to zoom in a little bit and make a measurement that is not a typo that running compression on this SKYACTIV to 5 is 331 psi now you combine high compression ratio with low manifold vacuum or high manifold pressure and with a cam that’s advanced that’s the kind of numbers that you can produce the test was repeated here it hit 340 psi so I’m gonna summarize this piece of this topic by saying that it is sometimes hard to guess on what compression should be yes once upon a time the compression ratio was an indicator of compression pressures but not so much today so you can see in just those couple examples so I’m just emphasizing how important is to have known good whether you get it from the manufacturer or you acquire yourself and you put it in your own database so step number one was try to get a known good compression spec step number two is we’re going to talk about pushing the pedal to the floor hopefully opening the throttle plate the example is going to start with a 2012 Hyundai Elantra with a 1.8 liter and we’re in service information and you can see where the red box is we have compression pressure specifications and a specification for this engine is a hundred eighty five psi so I have a spare

so the test is performed now blue is ignition primary voltage for reasons we talked about earlier and below that in the gold the amber is in cylinder cranking the engine over and the scale on your right is for my insulin or pressure transducer scale and you can see I’ve ran a horizontal cursor across most of the peaks and it’s about 180 psi not 180 psi is pretty close to the specified 185 so I’m ok with the 5 psi but there’s a few things I’m not okay with you heard me say that initially when you crank the engine over it’s possible that the very first compression pulse could be slightly higher than the others and that’s fine and you see that here however the second and the third are also a little bit high and then it kind of settles in and I know from experience that the first can be high but the second and third and the rest of them should all be the same if everything is ok if I’m following procedure and there are no problems so there’s something odd about that second and third pulse that I maybe I don’t understand or maybe I’ve ignored let me add something to this pattern so I’m not going to change the pattern it’s the same pattern but I’m gonna add something I know I was not showing you previously and that is the map sensor from this engine so the map sensor scale is on your right you can see what it says 4 volts so over here on your left that was key on engine off about 4 volts and the engine it then gets cranked over and you can see that the map sensor voltage is pulling down no so it pulls down it pulls and then right here it starts to stabilize and it’s now horizontal the fact that we can pull down a little bit says there is a slight vacuum in the intake manifold and if there’s a slight vacuum and intake manifold during cranking the throttle blade must be exactly right it’s got to be closed I didn’t open the throttle blade and you can almost see the relationship how the vacuum is pulling down here in red to my pulses that are higher until it finally stabilizes I’m gonna repeat the test and this time when I repeat the test I’m going to actually push the accelerator pedal to the floor and you will know that because if I push the pedal to the floor there will be no vacuum and they didn’t take manifold and the map sensor should represent that so but I’m interested in something else as well so here’s the test repeated and clearly my map sensor signal now is pretty much hanging around 4 volts so we know the throttle blade is open however look at the actual cranking compression it is now 212 psi and they’re pretty much even across the board even the first one so if I go back it was a hundred eighty so just by opening the throttle blade we went from 180 to 212 we picked up over 30 psi and that goes to show how how much of an impact manifold pressure manifold vacuum has on peak pressures and we’ll talk more about this but two variables that really impact your pressure in the cylinder are when the intake valve closes and how much manifold pressure you have in that intake manifold set another way how much the vacuum the lower the vacuum the higher the pressure in the intake the greater the cranking compression is going to be if I if that intake cam is advanced the greater the cranking compression is going to be which we kind of saw with the SKYACTIV 2:5 when it was in catalyst heating strategy so I hope I’ve made that point the importance of opening the throttle blade now what I’m not telling you to do is is forcibly open throttle blades I always depress the accelerator pedal and I realize on some engines the throttle blade will not open but that’s ok because it’s about technique and once you have a certain technique and you document your technique you document your results it’s always the same there’s no variation I don’t have to remember was the pedal open or is the throttle blade open or is the throttle buddy closed it’s always the same technique pedal to the floor so if the throttle blade is open throttle bit is open if it’s not it’s not but it’s a repeatable process the last point of my three points the first was pull us back second was push the pedal to the floor the third is visually look at those pressure pulses now you already know this so this is a known good pen estar three six in his Chrysler and I notice as I crank the engine over with the pedal to the floor that the first pulse is about 200 psi two volts but all my subsequent pressure pulses are nice and even that’s what I expect and as we go through the training program and you see all these patterns you should be looking for that that’s the expectation this is what I want to

see this is known good but even the 4200 that had a valve leak once it’s stabilized they look the same the SKYACTIV looked the same the two five in in the GM with the variable valve lift look the same so there that’s an expectation and usually that suggests to me that I have reasonably good upper and ceiling I have no intermittent problems now this is best explained with an example so we have a 2005 VW Jetta with a 2.5 liter BGP engine this is an inline five-cylinder engine naturally aspirated now the engine misfires I’m gonna show you a little bit scan data before I show you the scope pattern and I should say the engine misfires and idle so the scan tool is connected and I’m in the misfire counters and while I’m not gonna show you a lot of scan data I’m gonna ask you to take my word on this cylinder number two is the really the predominantly misfiring solar this is a solar that has the problem so right now it’s counting up there’s ninety three misfires on the scan tool however as the RPM is elevated right now we’re about 1200 RPM cylinder number two misfires disappear and I will tell you the engine stops missing so I can almost control the intensity of the misfire by moving the accelerator pedal so when I bring the engine down to idle it’s got a pretty good miss but as I elevate the rpm the miss starts to diminish and it’s completely gone by 1200 rpm which is sometimes a clue of valve sealing sometimes so a pressure transducer is connected now before I actually show you the results of cylinder number two I’m winning I’m gonna show you solar number one as known-good reference so here’s some number one cranking compression and my cranking compression is hitting approximate 184 psi my pressure pulses are very even as you can see the cursor across them this looks good this I don’t have a misfire in this cylinder the 184 is a good number and my pressure pulses are nice and even I’m gonna start the engine up staying in the known good Soner now normally when the engine is running I expect to see fairly similar pulses across the board but I have a you can see there’s a little bit of a undulation or a wave here and here’s the reason for that this is a five cylinder one of the five cylinders is missing this particular cylinder is not contributing to power because my pressure transducer is in it so of my five cylinder one of them this one’s got a completely dead miss another one has a miss so I’m really only running on three plus cylinders so that’s why there’s a little bit of a hunt in the RPM and you can see the isolation in this pattern but nonetheless it’s not too bad now we go into cylinder number two and I’m gonna do a crank and compression test wide-open throttle pedal to the floor and the throttle blade is open and you can see immediately there’s an issue it’s clear as day which by the way a compression gauge would not show but when I run my cursors across where I would called in good pressure pulses I’m about 186 very close to the 184 we saw on so number one let me make the pattern a little bit taller or vertically enhancing as it’s been vertically enhanced you notice there’s almost a rhythm or a repeating pattern to this you’ll see if I start at the left my pressure is good it drops down comes back up it’s good drops down comes back up it’s good drops down comes back up it’s good so there’s a look to this something that’s repeatable now it’s not perfectly repeatable but it definitely has a look and I want you to think about what valves do clearly as you crank an engine open valves open and close so air can come in air can go out but valves just don’t open and closed what else do they do as they are opening and closing of course you are correct they rotate so the valves are turning as they are opening and closing and this is a pattern that I’ve seen many times and some of you watching this program have seen as well this suggests we have a valve faced to valve seat issue now there’s some other possibilities and I would never say this means head job but I would say that we certainly have a valve sealing related issue let me show you how bad it is with the engine running so this is cylinder number two running compression and you can clearly see the repeatability of this sealing concern it’s good it’s bad it’s good it’s bad it’s good it’s bad and again on

engage and running compression unengaged is challenging anyway but a gauge would never show this relationship so now by the information I provided I cannot tell you which valve is leaking I I did diagnose that but I can tell you that there’s some type of valve sealing issue and my focus would be on the cylinder head side but more testing would be necessary than what I showed her my goal here is to show you what band looks like so before I move on to the next topic just want to remind you when you do a crank and compression test with a pressure transducer three important points are pull us back get an acquired known good if you can push the accelerator pedal to the floor and visually study the pressure pulses making sure that with the exception of the first pulse they should be all quite almost horizontal as you if you were to put a straight edge across them we hope you enjoyed this short segment of this training program and thank you for your time again this class will have three more parts that will be broadcast separately when you purchase one of our online events you will also get a digital copy that you will have access to rewatch as many times as you like please visit automotive seminars dot-com for class information and how to register we will see you then