I am definitely NOT a Blender guru. A geek maybe, since it facinates me and I do keep trying, but I do not comprehend 3D. Probably because my depth perception is borked (tic). Who knows. It just does not stick in my grey matter. The pictures are now missing in this old post, but it is generally easy enough to understand:
Import/export 3D models to/from game using S3D from skwasjer, the S3D author
Not having re-read it, but from my memory (look-out! low-flying plane!!!), you might have to un-check the quotes on the texture file name... ?? you might want to export the uv file, or rebuild it when finished with your regular obj edits. You have to link to the texture once in Blender, which I am not remembering how right now, but it is at least a two step process... every time I go to use Blender though, I have to use YouTube and search for a video for what I am trying to do, and specifically for my version of Blender, which is v2.8, and it takes me days sometimes to accomplish anything, other than a mess... I speak Korean better than I speak Blender, and all my Korean is from Taekwondo...
Kima Sogi!!! (some say kimo jahsay) "OWWW!!!" Notice also, that I cannot write Korean... Anyway, I pestered kapuhy no end for my last edits, and most of my troubles were solved when he suggested getting rid of the "smoothing" in the import and export dialogs in Blender. It did take me a while to find them though...