My system holds pressure throughout the day, but loses pressure over night. I've changed the the regulator and the fuel pump but still loses pressure over night. (no codes) I prime the system and it starts. Where do I go from here?

 

By explaining what engine/Year

 

2001 Mazda Tribute 3.0 V6

 

I'd not worry about it unless there is a problem with actually starting the engine , but the most likely thing is one or more than one injector is weeping under pressure over a long time during the hot/cold cycle or the o'rings are weeping slightly on the rail , those injectors can be expensive hence if that is the only thing happening i'd let it slide until things got worse :-) (i'm poor) , but it might just be a o'ring which are cheap .
good luck

 

Pressure was cut off from the regulator to the injectors and let to sit over night. Pressure from the regulator to the pump went down. All points to the fuel pump so I changed to a new one. Still have a pressure leak with no codes.