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Discussion Starter #1
This has been a fun adventure with the Chevy Dealership... 2017 Colorado 3.6L with about 35k miles, drove it for 2 years with no issues whatsoever. About 3 months ago started making this sound intermittently, sometimes it was there - other times completely gone. Can't hear it in the cab most of the time and can only hear it reflecting off of objects while driving with the window down. Seems to start quietly and gets louder as the truck warms up. Knock Sensor code pops up on ODB II reader along with a cylinder 6 misfire code.

Dealership has had the thing for 5 - 6 weeks over the course of 2 visits, along with another 4 hour wait while they changed the water pump. Each time I've picked up the truck no check engine light and it sounds fine, a few days later however... The video below is the day after I picked it up last. Put about 25 miles on it after picking up at the dealership.

At this point the dealership has done an induction cleaning on my engine 3 times and replaced: Water pump, 4 timing chain actuators, 1 timing chain, 3 fuel injectors (cylinder 6 fuel trim readings were all over the place), and a myriad of gaskets.

Anyone have any ideas I can take back to the dealer? Thankfully I'm still under warranty, but getting real tired of this...


 

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My lord it sounds like a diesel.

I'm going to guess lifter. Do we even have lifters? Maybe a bad cam lobe. But then there is that weird whine sound with it. Maybe two problems, like alternator bearing and lifter/tappet.

As loud as it is, it seems like they could find it.

Can you ever feel it miss? Since it has a code for #6 miss hopefully they at least took that valve cover off and checked it over.

Do you have another dealer near by?

EDIT: I looked up a pic of the lfx head, looks like there is a rocker arm of sorts, not sure what it's called, it's what the cam pushes on then that pushes the valve. Wonder if that is loose/worn whatever. Would guess on #6 because of the code.

Also there is the VVT gear on the front of the cams, those could rattle but it sounds too rhythmic I think, like that tappet/rocker. Very strange it comes and goes though...
 

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Discussion Starter #4 (Edited)
So here's what it sounded like a few days later after running a few errands... almost nothing.

I haven't felt the engine miss at all, I think the CPU is just seeing something weird going on on #6 and pulling up that error.

Also forgot to mention that the dealership changed out my knock sensors too...

 

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Looks like the OP has the LGZ engine, so the head may be slightly different from the LFX engine.
 

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Depending on the scanner, they still have the ability to kill each cylinder one at a time. That will usually always isolate which cylinder. (although, it does appear by the comments that its #6)

But from what your saying, this dealer is just throwing parts at it to see what fixes it,instead of diagnosing it properly.

Id be inclined to tell you to bring it to another dealer for a 2nd opinion.
 

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So here's what it sounded like a few days later after running a few errands... almost nothing.

I haven't felt the engine miss at all, I think the CPU is just seeing something weird going on on #6 and pulling up that error.

Also forgot to mention that the dealership changed out my knock sensors too...
https://chevrolet.7zap.com/pt/colorado/53123-2017/0-0-1894387657/0-1901565325-0-0/

Check out parts 14, 15, and 16. Rockers and adjusters. I would bet a box of donuts it's one or more of those on cyl #6

Makes me curious what the oil pressure is like too.
 

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Sounds like a bad valve lifter (adjuster) maybe loosing oil and collapses. . . thus making excessive noise. It would likely cause a "misfire" since the affected valve would not be opening properly. But, who knows what with the AFM cylinder deactivation which closes and locks valves shut when in the V4 mode. Maybe something is awry there. ::chevy::

EDIT: -
Here is a video of a collapsed valve lifter and what it sounds like on a GM V8. Not the same engine but gives an idea of what it sounds like. . . Very similar. Also, a video that describes how and why of AFM. Perhaps not what is wrong with your engine, but some insights of the wizardry and additional parts that can go wrong in these modern day marvels.
At least, an idea of where they maybe should be looking for at the dealer :


 

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Discussion Starter #12
So they had a specialist come in. He took one look at it and said it was a valve roller spring issue and something else. Instead of diagnosing all the small parts of the engine, they decided to put a new one in.
 

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New engine?
 

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Awesome. Its fustrating but a lot better than having them opening up yours, replacing some parts and hoping its fixed.
 

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I know this is an old thread and stumbled across it looking for something else. That noise sounds like a piston clearance problem, something GM has had issue with in the not too distant past. If the misfire code keeps popping up on the same cylinder, there's a very good chance that's what it was. The intensity has a tendency to change with engine temp also.
 
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