Engine knock? 16 denali

[jimr5454]

Hi.i am trying to buy a 16 yukon denali and when I tap the gass it has a wiered engine nock so I did it again and it happened again then the third time it didn't do it so I drove it a bit . turned it of and turned it back on and it did it again but not everytime.there machanic said its perfectly normal somth8ng about carbon build up on valves possibly so I tried it on a another yukon on the lot I was interested in and it did not do it .so I like this one the most and it is certified but I would like to know what that is so I atatched a link for the video I made of it doing it.thank you very much for helping me make a educated decision

 

[STORMIN08]

hard to tell in the video, but if AFM equipped...i would steer clear. the notorious engine tick/knock with these engines is a failing lifter, potentially causing catastrophic damage

 

[Tonyv__]

I think that’s the exhaust flap assuming you have that power sucking AFM system .. mine squeaks loudly but doesn’t sound quite like this

 

[jimr5454]

hard to tell in the video, but if AFM equipped...i would steer clear. the notorious engine tick/knock with these engines is a failing lifter, potentially causing catastrophic damage

Thank you for your comment .what is afm ?

 

[jimr5454]

Thank you for your comment .what is afm ?

Sorry I figured it out..active fuel managmant

 

[Tiredmechanic23]

its not continuous. I would get a zip tie and look at the exhaust flap and zip tie it open to see if it stops. If so nothing major wrong and its safe to buy. That noise is not normal operation but could be simple to solve.

 

[jimr5454]

Not to sound stupid but
Exhaust flap?
Thank you for your effort and time.

 

[sealandsky]

Not to sound stupid but
Exhaust flap?
Thank you for your effort and time.

Yeah I know, weird right? GM is trying to hide the unusual sounds of the V8 / V4 AFM so they devised a flapper valve in area of the exhaust collector. The flapper apparently cancels out the rougher exhaust pulses of the V4 mode. This is how it was explained to me anyway. Eventually the flappers wear and become loose and could potentially make noise. My 2019 Denali / Callaway has the AFM disabled and the exhaust flapper removed. You could make these modifications to your AFM and flapper on your vehicle and improve how it runs.

 

[jimr5454]

Thank you again for your time.
I havant bought it yet thats the main reason y I havant.so I'm going to have a independant inspection done and I will specifically ask about this sound of course and ask about this exhaust flap you mentioned.i am just trying to be cautious as possible and am weary of the issue these motors have with a few issues.mu 08 yukon has almost 300000 and have loved it but it is time to go on to somthing differant.
Could you tell me where that flap is located

 

[jimr5454]

So I took it to independent machanic and listened and agreed it is internal and very possibly a lifter failure issue but other then that and one small vacuumed leak ot is in very good condition. Took back to dealer this time he took it to there "#1" machanic and talked with service and said yes either way it will be repaired under warranty
Next week which is when there service departmant has a opening. They say they are leaving on the lot until it is repaired next for sale since it is under the warrantee and can't hold it till it is out of repair and if I want it I should buy it and have the repair done next week as its already scheduled but I am unsure if thats a smart thing to do and am looking for guidance?