So I have a 2007 Tahoe with about 174k miles on it. Driving home and suddenly got a violent dead misfire. Only code is P0306 along with service stabilitrak message and flashing CEL.

I went through general diagnosis of new plug, wire, swapped coil, tested injector. Plugged in the SnapOn Solus and all sensors are within spec.

Next step I pulled the valve cover and all rocker arms were tight with no play so I started the engine and #6 fuel valve was not moving. Being cheap i found a "youtube fix" and removed plenum and VLOM and tapped on the lifter through the vlom port. Had someone crank the engine and the lifter was moving fully. Put everything back together thinking I got lucky but to my surprise still have the same issue.

This is where it got weird. Pulled the valve cover again and had someone start it. Upon crank the #6 valve moves like it's supposed to but within 5 seconds of engine being on it stops moving. I replaced the VLOM thinking it was the solenoid and even did ckp relearn and cleared codes. Even left battery terminals off overnight and still having the same exact results.

I have confirmed that the lifter is not collapsed because it moves on crank.

I also found when I removed the plenum that all the intake ports were wet with fuel except for #6 which indicates that not only is the valve not moving but the injector is also not activating confirming that the cylinder is not being commanded ON by the AFM system.
My next guess would be ECU or wiring but I'm at a loss here. Any other suggestions where to go next?

 

Are you guys using Vista, per chance? I was able to activate it on my Windows 7 laptop, but on my Windows Vista desktop, even after a re-install and restart, it was not activating.