GM - Chevy Truck: Misfire Diagnosis

chevy thunder looks like a old four or five maybe 06 chevrolet it's the 1500 i just dropped her off brought her from one of the other shops he said he took it there well let me tell you the story what he told me is he took it to the other shop we'll call it uh they uh his complaint is the engine light's on and sounds like a misfire lights on lights flashing he said they did a number three coil and then a number four coil and then they seen that the wires were braided so this is gonna be a coil near plug from the sound of it so a coil and a spark plug wire and then they did the wires because the wires were braided and then you know still has the issue of this flashing light and the skip and then they uh he was told at that point once the coils were changed the only thing they can do is change the sensor not sure which one i assume maybe like a crank sensor and then they did that and then he still has a problem so then they told him major electrical you're gonna have to go to this guy in downtown avica and here he is so we need to figure out what's going on with it so we'll fire it up here she's definitely skipping let's put it in drive funny thing is though i've drove me a lot of shiverways and this does not feel like no contribution let's power break it slightly shall we ah i could be wrong that might be a totally dead hole yeah it's got a pretty good hitch in this video let's have a little listen as we crank it over that's always a clue so wide open throttle we're going to try to crank it sounds pretty normal uh but that can be deceptive even to the trained ear not that i've trained my ears but you know what i mean so let's pull it in and the reason that we do that crank no start there where we just whizz it over is because we want to hear does she sound like she got a dead hole so um let's get a scan tool on it let's see what cylinder it tells us is misfiring but it's weird at an idle it feels more low contribution than no contribution why is that important to note simply because you know that could be engine mechanical you know do we have a loss of compression but not all of the compression like let's say we've got 80 pounds compression uh so it still starts runs almost fires but not quite whereas if we had no compression or no spark or no fuel then we usually have what we would consider a dead hole where it's you know hard misfire at night oh you know truck shakes sometimes with a v8 though that can be deceptive um because you got seven other little guys making up for the one little guy that's not anyhow enough talk enough guessing let's get a scan tool and figure this baby out dang down 23 should have plugged her in last night and my updates are out really slacking here folks big time i need to renew my sub i just haven't had time yet we're gonna let this little guy go through and uh do a system scan as we would uh i don't think so uh too many questions mm-hmm oh my gosh what's it want my blood type i don't know i have a little gander here and i do see the number two is brand new you see i just work we rhyme that one up uh let's see what we got over here oh yeah that's not number two you didn't die start chevy guys number three and number four on this side is brandy new brandy new wires just like they said and as far as the sensors yeah we'd have to call underneath to see if it did get a crank sensor however the all-tell is now booted survey says random cylinder misfire and a large evaporative leak okay this is the one we're concerned with today let's hop into our misfire data just for poop and laughter let's fire it up cylinder three and four is what it tells us cylinder 4 has the most accumulation on it according to the history so that's interesting just giving her a little look-see here like i say she's not not shaking too bad fellas we need to find out is cylinder 4 really our culprit it appears to be here appears to be more four than three i don't know what the firing order is on these new chevys uh i'd be curious to know if three and four next to each other therefore giving us some false falsies on number three let's go put it in gear and see if that cleans it up a bit just because it doesn't feel like a multiple cylinder misfired let's put her in the drive now let's look at misfire data definitely more steady on four i'm going to give her a little throttle a little power break let me put it reverse case the brake lines below give her a little bit of throttle and we can see there were steady misfire at number four so it doesn't surprise me to see it registering three and four with no load okay so we're going to blame number four however we need to verify that so we want to go uh kill an injector here i don't know where where that's at oops click happy jerk um nothing there maybe special functions we should be able to shut off an injector blah blah blah here we go let's see okay so what we're gonna do let me let me close the door here in case we do blow a brake line i don't want to have to put a door on this piece of junk let's see so i'm gonna power break it here a little bit i didn't feel any change there what let me kill number one oh yeah big change i don't know if i can just kill one and it kills turns the other one back on you know what i'm saying if i go two dead one dead three dead so they're all enabled but when i kill four there is absolutely no change don't worry about the day we're not looking at any data we're just going with what we feel and what we hear yep so number four is definitely the culprit number three big change you know we probably could see it in fuel trim i don't know i gotta show you something let's see we'll kill number three yeah i say our fuel trim should should start to increase number four because anytime you have a dead hole now that cylinder is just pumping air so uh um look at this see our fuel trim for cylinder for bank 2 is really high i mean this tells us we have a misfire does that mean it's fuel related i can't really attest to that there's lots of controversy on that in my opinion the cylinder's pumping air it's definitely cylinder four let's find out why so does that make sense to you seeing that the fuel trim numbers are really high on this bank so this is bank two uh because we have cylinders you know two four six and eight over here i don't know the firing order but i know that much uh so when you have a cylinder that's not firing there's no combustion the oxygen sensor doesn't see it therefore it sees it as pumping air and and sees that whole bank is lean and then the fuel trims are high for that bank now i know uh some guys in a watch or some guys see they'll put their life on the line and say that 100 is fuel related yeah it's a fuel related misfire because your field trip numbers are high i would have to disagree because if i pull a spark plug wire off that side over there even though the injector is still working that cylinder is now pumping air and it drives the fuel numbers high on a speed density engine on one that runs with a mass airflow not a speed density engine a mass airflow engine rather so i never really banked my whole diagnosis on what type of misfire it is based on fuel trim alone i look at it i take it in consideration and then i move on with my light so what we need to know now is number four you know do we have spark do we have a good spark plug do we have compression you know is this mechanical is this ignition related or is it fuel related brand new coil brand new wire doesn't mean they're good sounds like they've been chasing this thing around so all i want to do uh is quickly verify you know do we have spark is the spark making it to the plug is it sparking if it is great let's move on and just like if you're in the business of skinning cats uh there's more than one way to do that and then what we're gonna do is we're going old school spark plug tester mother that's hot come on danny uh just simply because i can have this plug wear off uh faster than i can get out of scope and turn it on so what we want to know is is this coil firing and we're just going to hook this to something and then we're going to sit here we're going to start it up see if it's firing if it is um the spark plugs are brand spanking new so highly doubting that we have a bad spark plug but we can and we're not going to interrupt our process for an assumption because you know that whole process assumption and me and you and something to do with an a-hole and stuff like that so let's see can she jump the big gap right there let me go fire it up well yes sir you leave me on the levee let's make that up so we have spark out of the coil is it occurring at the right time we don't know more than likely because all the other seven spark plugs seem to be firing at the same time so what we could do now uh if we're so inclined to do so is we could pull the spark plug out and say hey did these guys just have some bad luck and get a spark plug that's you know carbon track down the side easily could see that on the scope if we had a scope we hooked it on where we could see are we firing inside the cylinder are we firing outside the cylinder does it appear to be a lean condition there's a lot we could gather from secondary waveforms and sometimes that's good to do especially when we find out like hey this thing's just got a bad injector then you could take your time to hook your scope up and say well what does this look like on a super lean cylinder and then kind of commit that to memory and use that in your diagnostic arsenal in the future when you get another car in that has a misfire that let's say it's not as easy to get to the plug and wire but you can get a scope on it you can look at that secondary waveform and say hey this one's rich this one's lean this is firing outside the cylinder so on and so forth but for this purpose on this video we're going to yank the plug have a visual inspection and then if it looks fine just swap it with another cylinder misfire stays on this cylinder we know we have spark we know the plug's good now let's look at engine mechanical and fuel old school so let's pop this uh plug out there i know you can't see much but it's just a standard plug removal so we'll get this out because some ac delcos i tell you what brand new out of the box they do have a tendency to get some carbon tracking on them or be cracked down the porcelain so we'll take her out she's white and shiny [Applause] hotter than a banshee covered with slime hi luna come here come here baby hi pumpkin what's in here baby say hi here's luna she just coming in it's the night out on the town take one side i just gave the plug a full cat scan and it came back good but that's not always a good test cause what do cats know so now come on baby what the freak hole so typically this is where i should just use the scope because guess what the plug wet super attached to the spark plug down there so we're gonna take that off now we're gonna take our spark plug wire this is from the number two and we'll pull it back in back in the hole everything's pretty hot and then we're just going to swap that plug because we know we're not having a problem with the number two cylinder so you see what i'm saying we'll do the old swaparoo it's called swaptronics it's not as bad as triagnastics because it is kind of like diagnostics but it doesn't cost us anything except a little bit of time and i'm doing this solely for your education educational purposes and as silly as it sounds uh even though many folks in the automotive industry diagnosticians they like to be called would scoff at this approach it is it is an approach that a uh you know that not only can be used in the shop but you know a diyer can do themselves simply because these parts are all similar the coils are the same the plugs are the same the wires are the same and if you don't have access to as scotty kilmer calls them your big fancy scan tools then this is a approach that a guy could take um and and sometimes even if you do have your big fancy scan tools you can still use this approach uh simply because it works and um [Applause] it's really limited by access to like and similar products on the vehicle you know are the coils are real pain and the hoo-hoo to get to are the plugs that you know son of a mother to swap around you know stuff like that where this here like i say is pretty quick and it's a good eliminator and i mean you can take it as far as you know if you had to you know swapping injectors but at that point it gets kind of silly but simple stuff like this you know the coil is a plug is a wire nope it's not ignition doesn't appear to be could it be still yeah but what are the odds you know head your bets baby you guys can't see crack down here so that's me trying to do kilmer impersonations make sure she's locked on she locked and loaded and of course this whole thing could go sour because if this had old crappy wires and the wire breaks and here's your judgment i guess what i'm getting at fired up still skipping oops we don't want to go to active tests we'll just go right back to the live data engine data we'll go to the misfire hope let me power break it a little but it looks like we're still having an issue with numeral four still got the problem in number four so there we go process of elimination we have a pretty good idea what it's not now this is where i could get burned by going diy-ish on it is listening to it crank over here we can have a listen again more inside listen closely so cranking over like that sounds pretty normal i could get burned if i had my scope out and i was looking at secondary ignition waveforms i'd boom throw it on the uh you know negative battery post or positive or whichever hook up the leads however we want to do it we do a relative compression test and say yep relative to each other they all look the same in my experience i'm gonna skip that which i shouldn't and we're going to do an injector balance test because we have our scan tool hooked up so what we'll do is we'll pressurize the injectors with the scan tool as a built-in injector balance test for these chevrolets and we'll turn on each injector and we'll see how much pressure it drops uh when we command those injectors on and we're gonna go right for the gusto we're not gonna do them in order we're just gonna go down that bank we might do cylinder you know three four and five and see if cylinder four is not flowing as much fuel as the others that's kind of fun just had a fellow stop then a local farmer down the road got one of these chevrolets and uh he's bleeding out his hand pretty good and asked me to change his number seven spark plug for him because as you know these afm engines and the later models are complete garbage and of course they burn oil and follow up the spark plugs and stuff so you keep spark plugs with them and keeps changing out the number seven every six months or so but he's a little frustrated this morning so i just went on the parking lot and changed his uh number seven spark plug so we could keep driving this chevrolet so what we're gonna do now is we're going to install this little guy so we're going to put on our fuel pressure gauge now i could be wrong here folks or we could be right i think those are lyrics to a song oh get that there and then like i say we're gonna turn the key on and the scan tool has an automated process of turning on the fuel letting it build pressure and then turning on an injector for a given period of time or pulses which equates to time and then we're going to see so we're at 60 then we're going to kick it on and watch it and see how many pounds it drops per each time it kicks on so let's do that let's get something right on so some people ask uh so click fuel injector balance like oh erico i don't have a no i don't have a big fancy scan tool that's okay because if you're doing an injector balance test it doesn't matter because you can buy a standalone device to do that a little injector pulsing tool uh i don't know ktool makes i have to look at my box they're quite inexpensive and you can get them on amazon and then they're universal for all you know electric fuel injectors like this not gdi um but this style electric solenoid type injector i don't know what else to call it so let's go injector number three let's see here so she just built up fuel that was quick a little bit better too much looking too much talking so i get you i need to do that again uh so when i push the injector button it's gonna build up fuel pressure we're going to look see where it's at record that and then watch the drop so let's do let's say let's do cylinder five hit the button 48 to 34. so 48 psi to 34 psi and that was number five so now we'll do number i'll let one build up there's 48 to 35 so 48 to 35 and that was number one now let's do our offending injector let's do number four just to see where that's at 48. nothing there's no clicking there's no nothing let's do number six 48 to 34 48 to 34 psi and that's number six now just for grins and giggles let's do number four again 48 psi oh injector has already been tested and unable to restart during this ignition cycle okay so it won't run the test twice because it doesn't want to swap the cylinder so uh we have a pretty good idea though from watching that either that injector has some electric problems going to it or the injectors just pooched which i would imagine if that injector was unplugged let's say it's open circuited broken power feed or a broken control wire i would imagine we would set an injector code like a p0204 i think that would be an injector code which we don't have so i assume that electrically it is there and it is the computer sees it as having continuity through it back on the control wire therefore the injector itself is probably garbage so let's just test that theory uh we're going to back out of here and we're going to simply just do that by starting it running it and using our test light uh or we could use a noid light so let's do that so busted out the old noid light set we're gonna unplug this injector here get our harness up out of the way get the little blue clipper up out of the way these things can be a real pest pot there we go there she is baby so then what we could do at this point is we could check do we have power here and then do we have control pulsing control uh or we could just shove a noise light in there and fire it up and see if it blinks which this one doesn't fit quite right and i don't want to spread the pins so let's just start it and see a couple things you know do we get a code for it which that would be nice and do we have a blinky light which would be even nicer so stand by now we're gonna go to codes and we're gonna see hopefully we threw an injector code injector control circuit po200 surprised it's not specific to that cylinder but what do i know and we have a pulsing i don't know if you guys can see it here turn off the light let me see what you see and we have a pulsing noise like can you see that i don't know you're gonna have to trust me but we have a pulsing noid light so that tells me you know we have the ability to fire this injector so that's that let's uh shut this junker off so now what we'll do is let's test our injector it must have some sort of resistance through it or continuity through it um because a lot of people right now are like oh you're an idiot you can't test an injector with annoyed light blah blah blah i understand that i also understand that that noid light draws about a half of an amp these injectors probably draw about three quarters of an amp and it lit up what seems to be about normal so calm down it's close enough test if we had no blinking at all then we would be concerned so we're going to check uh the injector here i would expect probably 14 ohms or so we can always compare it to no good but if let's say we're if we're higher than 15 we'll do something here or lower or higher or whatever but let's see we checked this in jack there and the survey says come on baby 14. ohms 14.3 ohms in my opinion that is perfect and that folks is why we have no um no code for it because that is what i would consider to be perfect that's really good let's do this let me turn the key on and show you something we have k-o-e-o kion engine off we're gonna pop back into our special functions we're gonna go hit the cancel we're gonna go to fuel injector balance and then we're gonna go to cylinder four and we're gonna make sure that our balance test is working properly where it fires this injector power up and then should fire bing bing bing bing bing see how nice and bright that is we are 100 being a shadow of a doubt making the call on a bad fuel injector it is a mechanically stuck shut electrically it is perfect therefore we have no codes but as we could see doing our balance test when we did that it cannot flow fuel even though we have control to it it will brightly light a noid light which draws almost as much current as a fuel injector um that's that we could easily put a scope on that and we could see our inrush current we could watch our ramp build up but we would never see a panel hump in it where the injector normally would open where we would see that mechanical movement of the fuel injector we will not see in this case perhaps i could show you that for you guys who are scope users where we could have thrown a scope on that scrutinized that waveform and i would be willing to bet that we will not see mechanical movement on it so let's let's do that just so everybody's happy we'll do it right here at the injector that way i don't have to find a fuse let me grab a capture here uh and then i'll i'll see if i can show you what's up uh we'll see if this works we're gonna try a good cylinder we're upside down are we upside down a lot of interference here okay let me uh let me try to set a trigger here uh edge triggering okay okay so we got a trigger set up uh we need to change our time [Music] because we want to be able to see what we can see trigger's in a bad spot let's put our trigger up here higher let's get a little more time i want a little better definition here and then let's change our scale here to one and whoa baby click on that bring her down um that is on a good cylinder let me change my time yet one more time we'll go to 500 microseconds here i was really hoping to see a more clearly defined panel opening we can see a little sag right there so this is as current being induced in that coil and typically when that panel opens when you get movement of that physical movement we have a little reduction in current which usually it's more of a clearly defined hump as you will and then of course the injector is on and then the injector shuts off so i see slightly here this may not be a good demonstration so that's a good cylinder let's go to our bad one now this is our bad one and i cannot definitively look at that and then look you in the face and tell you that yes i would make the call based on that waveform uh because i'd be lying to your face so there's there's not much that i can tell you there folks uh i was hoping that was going to be a better demonstration oops however this is perhaps why we uh why we test things multiple ways so that's a little frustrating hoping that was going to be better for you i don't see a clearly defined kennel hump looking at current usually it's more defined so that's a bad cylinder that's our dead hole this is our good hole must be i didn't didn't zero this little guy something's happening there there we go so again that is the good one and that is the bad one i'm looking at the leading edge here and now frankly i'm not going to scrutinize it too heavily because well we already know what's wrong sorry for such a poor demonstration with that i honestly thought that we would see something more definitive with the amp clamp but it's also a great learning opportunity because like i say you know we've proved the injector doesn't flow it's got everything it needs to make it flow um you know it's not engine mechanical nothing you know it's simply injectors receiving its commands coils getting saturated you know electrically it works it's physically stuck so you know take that opportunity grab your scope you know hey we got a known bad we got seven known goods look at them can i see the difference in the current flow uh with those you know look at the secondary ignition can identify a lean cylinder like i know this cylinder is dead it's gone it has no fuel what does that spark look like and can i discern that waveform that scope pattern from a cylinder that's firing good and then kind of like you know save that like this cylinder we know for a fact this waveform has no fuel this this one is pumping air how does it look you know do we see this huge lean spike at the end of the burn line you know the secondary ignition um you know what's that due to the overall you know kv spike um is it easier for that spark to ionize in a lean cylinder versus a rich cylinder you know you can start to see that take some of that stuff you learned in classes and kind of apply it like yeah or do you look at it like we just looked at this and been like you know i don't know i would have never been able to make the call i would have never made the call looking at using this scope with this clamp in that fashion and say yes that is a bad injector we could have done other tests we could have used the scope and a pressure transducer to look at injector drop on each cylinder because even just doing what we did we see there's a psi or two difference between a couple of them that we just tested so lots and lots of different ways like i say if you're in this cat skin and business you already know it there's more than one way to do things so but there's only one way for you to do something for me and that's for you to head to that comment section the questions the comments the concerns i'm gonna get an injector for this fella and you're gonna go down there and ring the bell the insti the facebook and just remember viewers if i can do it you can do it thanks for watching [Music]

Channel: South Main Auto Repair LLC

Views: 452,301

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Id: I2IgGenAX0Q

Length: 34min 57sec (2097 seconds)

Published: Fri Sep 10 2021