found this on a Jeep forum about the 4.0 with a guy posting about #2 and #4 not oiling on a new rebuilt engine....
"Engine has to be running for lifters to pump oil correctly....don't worry about it. Also it can take a minute or two (literally) for oil to get to rockers when engine has sat overnight and is first started. I have timed mine at a full 3 minutes on a cold day! Sounds strange but there is always enough residual oil on rockers to adequately lube them"
from another forum....4.0
"I was revving it a bit, and even at higher RPM's , still no flow. BUT !
We found out the problem(or what appeared to be the problem at least).
When i ordered the lifters from rock auto, they sent me 4 extra for some reason(same lifters, just 4 extra).
I took one of the extras out of the bag and tried to work the
plunger but it was froze up, stuck solid.
So i pulled the rocker arms off and tried to depress the plunger in the installed lifters, Zero movement.
I got an old push rod and gave the lifters a cpl whacks each with a deadblow and they freed right up.
Reinstalled & torqued rocker arms and viola! Oil flow through push rods is back, im happy as hell. "