Lifter Stuck?? But....

Ryan Bokros · December 28, 2016

Ok, so I know that there is and has been an ongoing issue with the AFM lifters sticking or collapsing entirely. I have a 2007 GMC Sierra 5.3 Flex Fuel 4X4 - 165k miles. Pretty regular maintenance, I am not OCD, but I try to do my best at around 3500 miles - full synthetic Mobil 1 oil, AC Delco Filter.

Here is my situation....

No ticking whatsoever (which I know is usually attributed to this), BUT terribly bad misfire on Cyl 4 (on the the AFM cylinders, I know) and throwing the typical 304 code with stabilitrak warning. Before pulling the valve covers, I checked EVERYTHING (well, except compression) - I checked plugs, coils, injectors, fuel and oil pressure, etc. That is what led me to go ahead and pull the valve covers to check for any slack in the rockers/valves (even though there is no noticeable tick. Initially pulling the covers, I was pleased with how clean everything was....and how tight everything was. No slack in the rockers whatsoever, from what I could tell the valve springs look good, etc!! Yay...but WTF is causing this?

Well, I fired up the truck and found that the intake valve in cyl 4 was not moving. BUT...when my wife got home, I had her turn the engine over for me so I could see it all without doing it myself. Here is what I am confused about - on start up, the valve moves...but only one time! It goes through the whole compression cycle then stops once the engine is running. If it was collapsed, it wouldn't push the valve on start up, would it? Could this be the VLOM and not the lifter? Thoughts?

Thanks from the new guy here!

Ryan Bokros · December 29, 2016

Surprised there isn't any response to this thread....

Another thought....would deactivating the AFM/DOD possibly cure this problem until I can get the top of the engine off to do the VLOM replacement? I realize that may be a temp fix, but this is my daily driver.

Thanks!

NSFW · January 6, 2017

I'm not familliar enough with the engine to lend any advice, not a fan of the engine you're having trouble with.

Do you have access to an online automotive troubleshooting service? Because I think a systematic run thru (with guidance) of any or all systems effected by might help to locate the issue. Sorry I couldn't provide you with any more help, I'm just not familliar with the engine.