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2008 Silverado AFM issue

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New User

Sep 19, 2015, 9:12 AM

Post #1 of 6 (1976 views)
  post locked   2008 Silverado AFM issue  

I have a 2008 Silverado with a 5.3 and active fuel management. Had a collapsed lifter for the intake valve on #7. Changed the lifter but on start up it acts like it is being deactivated, won't open the valve. Unplugged the system at the back and acts the same. If I turn the motor over by hand it works, opens the valve. Can't quite get why only one valve is affected. Can't quite understand why either lifter is affected. Haven't seen this problem on any post or fourm.


kev2 profile image

Sep 19, 2015, 11:37 AM

Post #2 of 6 (1964 views)
  post locked   Re: 2008 Silverado AFM issue  

have you considered AFM elimination kit?
you did get the new series (modified) lifter?
when engine running the lifter is collapsing - the difference is oil pressure could be a leak at the oil solenoid...did you scan for codes p3447 p34xx ? ? could also be mechanically stuck open.

(This post was edited by kev2 on Sep 19, 2015, 11:53 AM)

New User

Sep 19, 2015, 6:19 PM

Post #3 of 6 (1952 views)
  post locked   Re: 2008 Silverado AFM issue  

Not my truck so haven't considered a elimination kit. More because I don't know that would fix the problem.
Got the lifter from a dealer. They didn't mention if it was one that would work.
I am not that clear on how the solenoid works. Took them off and examined the seals and couldn't see anything obvious.. No scan. Didn't run long enough. Saw there was a problem and shut it down. If it was mechanically stuck then it probably wouldn't work when turning it by hand? I also am unclear why there was a problem in the first place. I haven't seen anybody in a fourm that spoke about why there is a problem with these lifters.

Thanks for your input

kev2 profile image

Sep 20, 2015, 7:56 AM

Post #4 of 6 (1931 views)
  post locked   Re: 2008 Silverado AFM issue  

I think GM suggests all lifters be replaced if you open it up.
engine off -turning over manually you claim lifter opens valve... but when started lifter collapses, SOUNDS TO ME AS IF AFM IS active...
why no scan? the solenoids and VLOM? will report issues. and a scanner will allow control over solenoids to help diagnose ?


Aug 9, 2016, 7:43 PM

Post #5 of 6 (1698 views)
  post locked   Re: 2008 Silverado AFM issue  

you may wont to look at the cam as well when i lost a lifter it took out the lobe on the cam still moved the rocker arm but not enough to fully open the valve and on the same hole i was told it could have been a bad cam or the cam break in was not dun right, i thank it is more oil related

Tom Greenleaf
Ultimate Carjunky / Moderator
Tom Greenleaf profile image

Aug 9, 2016, 8:06 PM

Post #6 of 6 (1696 views)
  post locked   Re: 2008 Silverado AFM issue  

Thread is almost a year old now. Please don't respond to old threads. Closed now unless the OP (original poster) requests it to be reopened. Thank you,


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