HELP!!! 2004 GMC Yukon Xl Denali 6.0 intake noise

iamdub

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Great theory! However, The cats and 02 sensors have less than 5000 miles on them, and the psst psst psst is coming from the top center of the intake manifold as opposed to the lower side where the exhaust manifold is.

I read on one thread where someone had broken the caps as shown in the picture here, but it doesn't appear to be leaning around any of these caps.

Oh well! It was fun picturing all of that. :D
 
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kaysha241

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Back to the drawing board then. Did you spray that carb cleaner near the throttle body? Can you post a video of the noise?
I have a video, but haven't figured out how to post it yet!

i did spray carb cleaner around it but no noticeable change.
 

iamdub

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So, if the intake manifold gasket blows out, can it create a vacuum leak under the intake manifold? An unmetered air leak?

An unmetered air leak is exactly what it would be. Grab some new gaskets and pop off the manifold. It's about a 3-hour job, taking your time, cleaning up under the manifold, etc. With the manifold outta the way, it'd be a prime opportunity to replace the knock sensors, knock sensor harness and oil pressure sensor if they're original. If you decide to replace the knock sensors, replace the valley cover gasket before you install the new sensors. Smear a coat of RTV under the hole covers, near the outer edges, to seal them to the valley cover.
 
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kaysha241

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An unmetered air leak is exactly what it would be. Grab some new gaskets and pop off the manifold. It's about a 3-hour job, taking your time, cleaning up under the manifold, etc. With the manifold outta the way, it'd be a prime opportunity to replace the knock sensors, knock sensor harness and oil pressure sensor if they're original. If you decide to replace the knock sensors, replace the valley cover gasket before you install the new sensors. Smear a coat of RTV under the hole covers, near the outer edges, to seal them to the valley cover.
@iamdub - Did you watch and listen to the video? In your opinion, is that what the sound is?
 

iamdub

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@iamdub - Did you watch and listen to the video? In your opinion, is that what the sound is?

I did watch it and listened through a 200W stereo :)

Honestly, with the sound and loudness, it sounds like a collapsed or turned lifter. But, there are too many factors such as your camera's mic, any noise cancellation software, etc. that can color what we hear on our end. Besides, if one cylinder had an ailing lifter, you'd likely get a misfire code for that cylinder, if anything. A random misfire code isn't very likely. An air leak can sound like a dozen other things depending on its size and location. Yours seemed awfully loud for the relatively minimal airflow going through the manifold at idle. But, if the leak is sized and located just right...

It seemed a little louder on the passenger side (although not as loud as the top center). Maybe start by popping off a valve cover and checking for slack in the rockers? If nothing jumps out, pop off the intake manifold. It'd be quite the rarity, but perhaps it cracked?
 
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kaysha241

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I did watch it and listened through a 200W stereo :)

Honestly, with the sound and loudness, it sounds like a collapsed or turned lifter. But, there are too many factors such as your camera's mic, any noise cancellation software, etc. that can color what we hear on our end. Besides, if one cylinder had an ailing lifter, you'd likely get a misfire code for that cylinder, if anything. A random misfire code isn't very likely. An air leak can sound like a dozen other things depending on its size and location. Yours seemed awfully loud for the relatively minimal airflow going through the manifold at idle. But, if the leak is sized and located just right...

It seemed a little louder on the passenger side (although not as loud as the top center). Maybe start by popping off a valve cover and checking for slack in the rockers? If nothing jumps out, pop off the intake manifold. It'd be quite the rarity, but perhaps it cracked?
Thank you for your input!
Actually, I took out the intake, replaced the valley gasket, put in the new knock sensors, new harness, and sealed it up this afternoon. You said it should take 3 hours, but that is as far as I got in the 3 hours. lol
I was having a hell of a time with the throttle body coolant lines and I ended up just leaving them attached and removed it from the intake)
I will clean up the intake and get it back on this weekend and see how it runs then.

Thanks again!
 

MO VietVet

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During disassembly did you see anything that would have caused the problem you are experiencing?
 

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