Hello fellow Ford enthusiasts. I'm a frequent visitor making a first time post to see if anyone can help me identify this line that I found disconnected between the engine and the firewall. (Images attached, circled in red.) It seems to diverge from a second line that I couldn't quite follow all the way back.

This is a '94 Ranger, 4.0L V6. On another note, does anyone know A) what the outlets are that are circled in yellow and B) what the OEM part number is for a proper plug replacement?

 

Welcome to the forum

That is the Vacuum Manifold, not all the ports are used and usually have Caps on them.

You have an automatic transmission?
If so that open line runs to the Vacuum modulator on the A4LD automatic trans
If modulator was leaking then previous owner may have removed vacuum hose to prevent ATF(auto trans fluid) from being sucked up and into the engine, makes engine run like crap.

That modulator hose just connects to a vacuum manifold port.
Put a hose on the end and suck on it, if you can suck then stop, or you will get a mouth full of ATF

There is an access panel under the carpet in the cab to get at the vacuum modulator, if exhaust system is in the way.
Or you can just leave it as is, vacuum modulator is the "kick down" when you want to accelerate, cruising along vacuum is high, when you push down hard on the gas pedal vacuum drops to 0 and vacuum modulator would cause down shift if needed

Picture here of where modulator is located: http://www.therangerstation.com/tech...ld_labeled.JPG
Passenger side toward the back

 

RonD, just wanted to say thank you for pointing me in the right direction, and yep, auto transmission. I suspect you're right about the previous owner intentionally disconnecting it - though I haven't performed the test you described, the port on the vacuum manifold looks like it was sealed with a piece of tube.

I may need to replace the rear crankshaft seal in the near future, would that be a good time to replace the vacuum modulator as well, with the transmission dropped? And would the increase in performance be noticable, for example in passing other vehicles or briskly accelerating from a stop?