Enlarged neg DEV?

I am trying to make some enlarged negatives using some FUJI med film I got for free, its a single emulsion blue base. I have tried it in a pinhole camera and it seems to work ok but when trying to enlarge a 4x5 neg the positive comes out very muddy and neg even worse? Could it be my developer? I am using D-23 3:1. Could I be just overexposing the hell out it?

I think you need to try some other developer. When I did enlarged negatives on Efke OP-12 I seem to remember (about ten years ago now) I did the first positive in Ilford Multigrade (print developer).