when i make assets in Blender and import in UE4 after try to use the grass , AFTER USE AND build light my grass become black when i see for back side fix plase and help ///
I created a grass leaf texture (spared no effort, look at attachment) and recorded 2 videos to show how I would create grass foliage the “easy” way. Maybe you could explain how you created your grass and what settings you are using for your material. In the video of Unreal I use dynamic lighting.
Blender : blender_tut.mkv - Google Drive
Unreal : unreal_tut.mkv - Google Drive
Your problem could be caused by static lighting. If you want to use static lighting I would recommend using a stationary light source and setting your foliage Mobility to Movable (when in Foliage Mode) 
