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Discussion Starter · #1 ·
Have a 2018 3500 l5p GMC Denali while descending down a hill and exhaust brake comes on getting a high-pitched squeal that sounds like a metallic rattle been to the dealer say I have no problem with up pipes did smoke test from tailpipe also said could not duplicate the sound at a loss turbo seems to be good and tight don't see any buildup around exhaust almost sounds like the turbo veins are rattling and squealing any thoughts would be appreciated
 

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Welcome to DieselPlace

Checked for any codes?
 

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Discussion Starter · #3 ·
Does not throw any codes at all when truck is empty unloaded not towing hard to duplicate sound unless going down a Long Hill and it down shifts squealing will get louder when I have a trailer behind me my empty dump trailer weighing 5,000 lb it will do it all the time when the exhaust brake turns on and functions
 

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Does not throw any codes at all when truck is empty unloaded not towing hard to duplicate sound unless going down a Long Hill and it down shifts squealing will get louder when I have a trailer behind me my empty dump trailer weighing 5,000 lb it will do it all the time when the exhaust brake turns on and functions
It almost sounds like a clamp is a little loose allowing some pressure to blow past
 

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Discussion Starter · #5 ·
Would have thought something like that would have shown up when they did a 15 PSI smoke test in the tailpipe with no pressure drop at the dealership
 

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Would have thought something like that would have shown up when they did a 15 PSI smoke test in the tailpipe with no pressure drop at the dealership
It might take more than 15psi to get the condition to appear
 

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My PX-7 (ISB 6.7) in my Peterbilt developed the same thing. It was a bad exhaust port gasket. Tier 4 or not, there'll be soot at the leak point, whether it's a clamp or gasket. And it'll be between the cylinder head and the turbo, whether it's a manifold gasket or even an EGR gasket (remember, the EGR cooler is before the EGR valve).
 

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And, it never sounded like an exhaust leak. I could pull the same hill in blairsville @ 53mpg and not hear a thing, or see a power loss or see higher EGTs.
But, come down that hill, and the grade is just right that when the cruise is set @ 55mph, my truck will alternate brake and throttle, and the squeal is only when the VGT engine brake is active. BTW, my truck scales at 25,940 all day long.
 

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Discussion Starter · #9 ·
As far as finding soot around any place nothing around EGR, up pipes ,manifold. only place I find soot is around actuator shaft on turbo for the vanes
 

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Discussion Starter · #10 ·
As far as pressures developed when exhaust brake activate no idea how high that pressure is would somebody possibly be able to tell me
 

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