while changing out my fuel injector o-rings i notice i have some oil in my intake manifold. i recently changed out the separator so i'm wondering what would cause this. it seems as simple as pressure in the crankcase but i'm not sure why

 

There is only a few places for oil to get into the intake manifold, The separator(as you pointed out), the tube from the other valve cover, or sucking oil from the lifter valley(lower intake manifold gasket).

 

hey now thats something i had not considered. it's in the upper manifold would that happen if it was getting in through the valley?

 

probably not, would have to be coming from one of the two crankcase ventilation tubes, there is a low vacuum tube on the drivers side that is usually before the throttle plate and the high vacuum side after the throttle plate. those would be the only place for oil to get into the upper plenum of the intake. As far as I can tell. Here is diagram

 

it appears to be getting in on the high vacuum oil separator side based on the fact it's not oily on the TB side. i wonder if a better oil separator could be had. i lose about 1 qt every 1500 miles.

 

You might think about pulling your valve cover and making sure the oil return passages are free from gunk buildup. Sometime too much oil is in the valve area because it cannot return to oil pan fast enough. You can use clothes hanger wire to open up the passages. Just a thought.