What's this hose?

Before I go getting all obsessy, or rather, compulsey & remove the plenum, what would this 3mm hose front & center circled in blue be for? Also, the foam covering, red arrow ? - is that all it is is a basic piece of foam tubing that if it so moved me, I could pick up at home depot or some such?

& I got'a say, taking pics like this is a great way, depending on how you look at it, to see stuff that needs attention.

 

I don't see a picture.....

 

Yup. Flaked it. It's there now.

 

The blue is a vacuum hose and the red is foam covering. Home Depot should have similar.
You will find vacuum hose at an auto parts store.

 

Just happen to have a series of pics done for another member with similar questions.

The foam stuff is just anti chafe, could be replaced with just about anything.

The little line is simply a vent. It carries no pressure or vacuum. The metal part below it is the fuel pressure regulator (FPR). The line's sole purpose in life is to direct fuel to the intake in the event the FPR suffers an internal failure (fuel leak). Somewhat better than letting the fuel drip on the hot engine/exhaust.
Earlier engines had the line going to a vacuum switched valve and used engine vacuum to modulate fuel pressure. Again, yours is just a vent.

Red arrow is the FPR, yellow is hose in question.



Looking from front to back under the intake.



Connection to the intake tube. The line should always be dry. Wetness would indicate a leaking FPR.

 

Thank you. I am changing out the hoses & didn't see the hose in the vacuum hose diagram. I removed the throttle body to get at the hoses that attach to it & then saw a few more & then the 3mm one. Good to know, however I may wait off on that one til I have something else in mind I could do whilst I have things pulled apart. Unless there' some hiding below, I will be stopping short of two. There's a three way at the back of the bay. I removed two, however I realized that if I removed the third, I'd have a heck of a time getting the new one on as is.

 

Thank you. I really appreciate the "how this works"!

 

& as light dawns on marble head, because of your through explanation & pics I see that what I thought was running under the lower plenum, hence why thought I'd have to remove it, is actually supposed to be hooked up with that there vent. It's probably been like that since I did the valve cover gaskets....

& what a flake cuz when took this pic I didn't realize this vent had been hoseless all this time. I guess I thought I had removed a hose from the other side earlier in the job? Yeah, yeah, that's it....

Also, that these should be replaced with fuel line, not silicone. & there are two hoses off the charcoal canister that I'm thinking should be fuel line....

It'd be really cool to have a full diagram or schematic of all the hoses & what they're for.