I keep having issues saving 100% black using illustrator or all my line work. When I re-open the files the colour defaults back to a dark grey. My files are CMYK not RGB. I can't figure out a solution.

I am creating my artwork in illustrator, my line work both stroke and fill need to be 100% black so I ensure that my CMYK is 100% K, I then save my file.  When I re-open the file in illustrator the CMYK defaults to a dark grey every time.  

My output has to be 100% Black.

What is going on and how do I fix this. 

Someone please help.