LimitedSlip11

So I have a 2008 Avalanche 5.3 w/ AFM. 76k miles. It recently developed the chirping/knocking noise that has been associated with the AFM lifters. Almost sounds like a belt squeak but it is too rythmic. I have listened with a stethoscope and can be sure its not a belt or accessory pulley or anything. I have done a lot of searching on this but have yet to find answers to a couple of questions I still have.

The noise will go away in V4 mode when I let off the gas on the highway or coming to a stop. Dead silent. As soon as I hit the gas or the engine returns to idle, its back. Why would the noise stop as the lifters are still moving?

Second, it does not make the noise at cold startup and it will start 10 seconds or so later. Seems to get louder the warmer the engine is. Could this be due to oil thinning out a little as the engine warms up?

Its not throwing any codes and oil pressure is good.

Sounds like this.....

Thanks for any input.

sledge.impy

I googled up lifter noise.


Have you been good on your oil changes? From this video here, I saw another video where the guy put in transmission fluid and out came a ton of sludge oil crap from his motor.

I would've liked to see this guy pull his intake off and inspect the lifters/camshaft lobes:



Anyways - I'm not sure about where you water pump is located on vortec, but pull off your serpentine belt to eliminate anything else besides the motor from being the problem.

Not hearing anything that sounds exactly like yours.

LimitedSlip11

I have been very good on oil changes. Every 3k miles. Full synthetic. I did buy it used though with around 50k miles. I have found a few videos with this particular noise like the one I included in the original post. All I can find is people commenting saying its the lifters but again I am not sure why the noise would stop in V4 mode.

After looking into AFM a little more, it looks like the lifters still get lifted by the cam in V4 mode but the pushrod and rocker arms do not. So possibly something else is causing the squeak/chirp?

sledge.impy

I found this.

http://www.justanswer.com/chevy/2adv...work-5-3l.html