Ok i just bought a 1987 6.9.t ruck ran great for a month o r so it will now loose its primeand you have to prime the filter or it will not crank what can this be

 

Are you leaking fuel anywhere?

Check the schreader valve on the filter itself. Also, check for leaks around the water seperator if seperate.

Is it wet or is their fuel otherwise obviously leaking from near any of the injectors or the return lines?