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Knocking / Rattle when entering and exiting V4 mode

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2007.5 nbs SiveradoI LTZ 6.0L


I've been reading the forums up-and-down and can't find anybody with similar problems. kinda.


My truck starts no problem, it idles nice and smooth. With no noises. And when running in V8 mode I hear no noise 1st 2nd and 3rd. Power is normal.


The knocking / rattle happens when I let off the gas and the truck enters V4 for mode. I can hear a click when it does this. Then when under very slight acceleration while still in V4 Mode I start hearing a very loud knocking / rattle under the glovebox area. If I keep the truck in this position and staying in V4 Mode the noise will continue forever until I give it a little more gas and it switches to V8 mode. There is no vibration at all, and no codes are thrown.


The sound seems to be rotational and related to speed and or RPM and it gets louder the closer I get to switching to V8 mode.


I have checked the flex plate, it is fine


Any help at all would be greatly appreciated







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My truck is a 2007.5 new body style 6.0 Vortex Max L76 Holden with L92 Heads.

I believe the problem started after my most recent oil change.
I do have a tuner from Black bear. When I disable AFM the truck runs totally normal in V8 mode. No noise no lifter noise nothing period
I'm thinking the oil passages to the lifters for the AFM might be clogged.
Any ideas? Should I do a major engine flush
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GM said it needs a new Engine. Bad phasor and 1 or more failing lifters. Cheaper to put a new engine in than change lifters and phasor, camshaft position Actuator P/N 12585994. AFM is toast.

Has anyone had GM help them out with $$$ towards this problem?
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GM said it needs a new Engine. Bad phasor and 1 or more failing lifters. Cheaper to put a new engine in than change lifters and phasor, camshaft position Actuator P/N 12585994. AFM is toast.

Has anyone had GM help them out with $$$ towards this problem?


Your truck is 10 years old. Warranty has been gone at least 5 years. GM owes you nothing. You did not buy a truck with a lifetime warranty. Man up and pay for it yourself like everyone else.

Edited by O_J_Simpson
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Just out of curiosity how many miles are on this thing? Regardless it's kind of a catch 22, if the chassis and rest of the drive train were perfect I might toss a new engine in it. But a 10 year old truck will have the usual PIA electrical issues so a better idea might be to trade it off.

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