I've tried about everything and I'm out of ideas. Loosing prime after replacing the filter head. Pulled the return off the cp3 and capped it off,pumped the primer bulb and the system held pressure. Even pulled a vacuum one the return side of things and it held. But when I prime it with fuel it looses pressure slowly overnight?. Replaced the driver side return line when the injectors were replaced, injectors were from merchant auto. I was thinking it could have been a fuel leak at the cp3s shaft seal. Any possible thoughts?