Misfire Diagnosis w/ Scope on GM 6.2 NOT from a Lifter !

In this video I show how you can use the scope to correctly identify the cause of a misfire and to help differentiate between different valvetrain components. This was on a 2015 Cadillac escalade with a 6.2 liter V8 ls engine.

[@neverstoplearning382]

Amazing how clear you explain everything Sadel. Thank you very much for taking the time and make us smarter. God bless.

[@DTEAuto]

Glad it was helpful! and thank you for watching as always!

[@jimbo427vette]

Again: nice explanation of what is going on with intake wave forms and in cyc. Trying to break the details down is tricky and you have given a great detailed piece by piece tutorial. Thanks. Goes to show you always can learn something new>

[@DTEAuto]

Glad it was helpful!

[@djosbun]

Excellent analysis, Sadel. During until cranking it was easy to hear the dead cylinder but it did improve after the first 2-3 seconds, which I’m assuming due to rising cylinder pressure. Why the reemergence of the cylinder drop, that’s a tough one! Really well done, brother.

[@DTEAuto]

my best guess would be from the valve's continuous spinning in the head, that at some point it spun to where it could seal better against the seat and then other times it spun to where it would not sit against the seat and would bleed off

[@lucianlucian9911]

Sweet, man. Thank you for sharing your knowledge with us!

[@DTEAuto]

thank you for watching and glad you enjoyed

[@roderickzappareynolds2316]

Excellent video! Thanks for sharing!

[@DTEAuto]

Thanks for watching!

[@dtandfam8100]

Awesome video man! At first I was thinking a GM AFM issue.. But after seeing that valve spin, never mind! 😂 Awesome work on this and kudos on the different waveform analysis!! Awesome! Thanks for sharing!!

[@DTEAuto]

Yeah I figured most were going to think towards an afm lifter issue... but I tried to make sure to not sway it that way and explained the waveforms as best as I could to truly show the issue at hand. Thank you for watching

[@dtandfam8100]

Lol guess who didn't read the title!

[@secretsquirrel9722]

Love the depth you go to Sadel. I was super stoked with myself for guessing this one. With the history you explained. I guessed either a bent valve or a valve that had become slightly eccentric. My reasoning = the way it would fade in and then out in a smooth curve (spinning into, then back out of sealing better). I'm 100% certain you know from your background that valve systems are designed to slowly spin the valve during operation to minimise stress and wear occurring in the same place. Maybe the same test carried out longer would have displayed this repeatability. Also, wouldn't this be prime for a leak down test before disassembly? It would also be super interesting to do a leak down when the scope showed it in the low of compression compared to when the valve was in position for it's peak ability to build compression.

[@DTEAuto]

Yes definitely this is due to the valve spinning and at some point sealing better than other times which obviously didn't build up compression. And yes for sure leak down would have been interesting, but dunno how hard it would be to physically spin the engine over by hand to guess at which point the valve was sealing better than other times to do leak down. Other than that, that's great you guessed correctly and thank you for watching as always!

[@secretsquirrel9722]

Yes, of course I was being a bit ambitious in thinking you could time the sealing level of the valve. I forget just how much detail is shown with the scope when in real life, the frequency of that cycle could be multiple times a second. 🤪 And it's easy to look tall when you stand on the shoulders of giants, in regards to my educated guess. Like a student coming to an answer to an equation before the teacher says the answer. It's only because you had done all the hard work of testing and conveying what was happening that I got there. Being able to read the book is very different from writing it! It's not lost on me that that ability has come through people, such as yourself. Sharing and teaching what you know on the regular. I only wish my apprenticeship was as comprehensive! I might have stayed in the trade.

[@johnboutsikos6049]

Really superb presentation and explanation

[@DTEAuto]

Glad you liked it and thank you for watching.

[@DustinTSpeed]

Super helpful!

[@DTEAuto]

Glad it was helpful!

[@bartscave]

Thanks! It helped when you divided the720 degrees into four sections which showed the affect on the intake then exhaust waveforms.

[@DTEAuto]

Yes it definitely did, I too was having hard time comprehending it because the "small " columns make you look at it different but it's clear as day when you break it down to the 4 strokes for that failed cylinder.

[@advancedleveldiagnostics]

Really great video, Thanks! Great explanation!

[@DTEAuto]

Glad you liked it and thank you for watching!

[@mowlaascencio7897]

So great

[@R3YNZ]

Awesome video and explanation! 👏

[@DTEAuto]

Glad you liked it!

[@JoelAutomotiveInaction]

Another great video

[@DTEAuto]

Thanks again!

[@robertmobileman8304]

great video and content , thanks for sharing your knowledge

[@DTEAuto]

Glad you enjoyed it and thank you for watching

[@WhoDatPA]

Great video. I guess you just added some green food coloring to the alcohol for making it easier to spot or was it something else you used for the green color?

[@DTEAuto]

They actually have some that comes that color, think it's "mint scent" and I also believe they have purple. Thank you for watching

[@EGarcia_818]

Thanks for the video it’s leading me to believe I have a bent valve since I’m having the same symptoms. I bought a 2008 Silverado 5.3 with a cylinder 4 afm lifter collapsed and I installed new lifters and now that it runs nice and quiet but it has a rough idle on cylinder 5 and misfires but once you rev it up it smooths out. It does have the same exact crank rhythm at the beginning where it’s down a cylinder and then it gains compression. I’ll be removing the head mostly my issue here.

[@DTEAuto]

hope you get yours resolved and hopefully this gave you some insight

[@EGarcia_818]

Discovered that this engine was recently rebuilt and turns out to be an issue with the intake valve not sealing properly. I did the leak down test with alcohol it immediately started to drip had a puddle of alcohol within a minute.

[@alexandrabetke]

👍 👍 👍

[@brcisna]

Thank You for posting this detailed scope tracing scenario. Just purchased a 2010 Suburban that previous owner done and AFM delete on.After he got it back together it has never idled correctly. Bought the truck as is. Got it home has zero compression on cyl5,,OK,,problem found,,,BUT checking with heat gun on exhaust cyl 7 also is producing no heat. Have switched coil,plug wire, plug, and injector from firing cylinder and still producing no heat along with misfire counts almost as rapid as cyl5(no compression). Think am going to purchase a decent scope just to try and learn something from all this.BTW. Did you ever figure out what caused the valve to get bent on this truck. The owner of my truck said this truck run fine before he done the AFM delete kit on it. Thanks again.

[@DTEAuto]

The valve was bent from previous timing failure, and it's always a good idea to learn the scope to better your diagnosis, thank you for watching

[@stevepark5504]

The bent valve ties into the discussion about how(mechanical process) these engines sometimes bend pushrods. There must have been valve to piston contact to bend the valve. So what was holding the valve open at that time?

[@DTEAuto]

yes , you are correct. the bent pushrod was from the timing going off and the piston contacting the intake valve and the pushrod became the weak link. obviously, the valve didn't survive as it got bent as well.

[@danman9017]

tks

[@robinhood1188]

Low tech diagnose is hook up a vacuum guage!

[@reirizjose]

Happy S Patricks.!!

[@mayowaodus6310]

The Rc test showed the number 3 cylinder with a double hump which suggested an issue with one of the valves. I enjoy watching your videos but you still haven’t responded to my email. I understand is the nature of our work

[@DTEAuto]

Thank you! and I replied to email, thank you for watching

[@ousmanesarr7287]

You dont like pico 7?

[@DTEAuto]

No I do not

[@ousmanesarr7287]

@@DTEAuto can pico 7 show all 8 channels?

[@ousmanesarr7287]

At first i didnt like pico 7 also but with time am getting over it. I like the day and night mode for example . And the phase ruler appearance. But pico 6 seems more professional and straight to the point.

[@DTEAuto]

yes pico7 will work with the 8 channel, I just don't like how pico 7 keeps lagging and freezing up and slows down the computer

[@nickayivor8432]

ScannerDanner was right about DTech Engineering Sadel 👍 My Mentor DTech Engineering Sadel INTELLECTUAL DTech Engineering Sadel Brilliant video tutorial amazing thank you Take care and have a great weekend with all your family around you INTELLECTUAL DTech Engineering Sadel From Nick Ayivor from London England UK 🇬🇧 ⏰️ 14:34 Good Afternoon