If you have drawn your objects using vertical polygons then the explode will produce 4 3d lines for every polygon (1 at the bottom of each polygon, one at the top, and one for each of the vertical sides). The
3dline convert macro will leave any vertical 3d lines unchanged, so you will need to erase them manually (hopefully not that difficult using an entity type mask). You will also probably want to delete one of the 2D lines (either top or bottom), most easily done using the 3D erase command in an elevation view