Like everyone else already said, that is the fuel pressure solenoid. That piece is in between your intake manifold and your fuel pressure regulator.

Under normal operation, that solenoid is open, allowing vacuum and pressure from your intake manifold to lower and raise your fuel pressure. Most important is the raise in fuel pressure under boost. Otherwise you would run lean.

The solenoid closes under certain conditions, like start-up, so that the vacuum in the intake manifold doesn't decrease fuel pressure, so this gives you slightly more fuel pressure at idle, enableing you to run a little richer during a cold start.

You said that there is another nipple on the solenoid that you are now using. I think that may just be an always open source, meaing the solenoid is not switching that source. If that is the case, I would recommend to simply bypass the solenoid altogether, meaning take a hose and connect it straight from the intake manifold nipple to the nipple on the fuel pressure regulator. Or, just buy a new fuel pressure solenoid and be done with it, like you mentioned.

Here are a few diagrams from the SM to show you the routing.




Eric

 

Thank you for that diagram, that is exactly what I was searching for in the first place.. I'm on the hunt for a new solenoid now, as I'd prefer not to bypass it really.. Also, thanks for the great explanation and for helping me out..