In the attached image, what is the circled part? It is located on the fuel line between the fuel pressure regular (mounted on the firewall) and the passenger side fuel rail. I've checked online part stores, and nothing fuel or emissions related looks like this. I've consulted my dad with his repair manual, and he can't find any reference to it at all.

Thanks for the help.

 

I can't tell for sure from a distance, but it might be a vacuum fuel pressure regulator. The reason to reference engine vacuum is so that there is a constant pressure difference across the fuel injector, to make the fuel metering more consistent over a range of operating conditions.