That's an a/c line, not vacuum.
A leak in the 4x4 system would only operate the pump if 4wd is selected. Since the solenoid keeps it segregated (unless the solenoid is faulty).

With the key on, disconnect the vac line heading to the firewall. It's seen in the first pic, clipped to the cowl bracket. It looks like it's been messed with as those connections aren't factory.
Disconnect it as close to the reservoir as it goes by itself. Then plug the reservoir end with your finger. Wait a minute. Does the pump stop?

 

Thanks for replying Kaya.
That's what I thought on the a/c line, but wasn't sure if there might be a vacuum line present in there somewhere.
I disconnected the line running through the firewall close to the reservoir; plugging the reservoir side the pump does not stop even after a few minutes. Would that mean that the reservoir itself has a leak? I did use a vacuum hand pump directly to the reservoir yesterday and it did seem to hold vacuum pressure...

 

Huh that is odd.
Just for the heck of it, disconnect the line from the pump going to the reservoir. Block the port.
Does the pump stop?

 

Yes if I block the line from the pump it stops.

 

Any 4x4 solenoid other than Ford will leak internally, if you have a hand pump you can test this. Been down that path, bought a Ford to fix the problem.

Contact these fine people for the part:
https://parts.autonationfordwhitebearlake.com/
.

 

Pull the hose off the 4x4 solenoid, then pull the hose off the vacuum reservoir. Put the hose from the pump onto the solenoid port that runs to the reservoir(bypassing the reservoir) so that the pump is only running to the solenoid and no where else -- does the pump shut off?

 

Test first by isolating.
Disconnect the line heading to the solenoid. It should be coming from the firewall. Plug it.

Edit: beat me to it haha.
Albeit another method

 

Since you have a hand pump, isolation testing will soon show the problem -- loose connections, Doorman solenoid, Doorman solenoid

So far I have tested 7 Doorman solenoids, all failed -- the parts houses love when I bring my vacuum tester -- I cheaped out and went that path before I got an OEM part -- tested 2 Ford solenoids, both passed.

I think you may have had a problem elsewhere(hubs, lines) but the 4x4 solenoid is it now.
.

 

This video from Ron helped me out.


Sent from my iPhone using Tapatalk Pro

 

Thanks Hydro. You nailed it, it was the vacuum solenoid. I had previously purchased 2 of them thinking there were issues and they were both leaking, I never thought to hook the hand pump up directly to the solenoid to see if it would hold vacuum. I went to my local dealership and bought the oem solenoid and problem solved!
I do have a strange issue that maybe you have a thought on though... After hooking everything up to the new solenoid the vacuum pump continued running for a few minutes to build pressure but only stopped initially after I squeezed the rubber boot on the reservoir feed line to make it stop. After I did that it stayed stopped, and just thinking it was coincidence I created a draw on the vacuum and got the pump running again to recreate and I had to squeeze the boot again. Thinking it might be the boot I used a tight fitting rubber hose from the pump to the reservoir with the same result. So I'm making headway but it won't be solving my original issue of the pump constantly running if I have to squeeze off the supply line to get it to deactivate the pump. Let me know your thoughts when you have a chance...
Thanks again for your help!

 

Thanks for your help as well Kaya, I have one more question that I replied to Hydro that I will paste below to you as well so feel free to jump in if you have ideas.

After hooking everything up to the new solenoid the vacuum pump continued running for a few minutes to build pressure but only stopped initially after I squeezed the rubber boot on the reservoir feed line to make it stop. After I did that it stayed stopped, and just thinking it was coincidence I created a draw on the vacuum and got the pump running again to recreate and I had to squeeze the boot again. Thinking it might be the boot I used a tight fitting rubber hose from the pump to the reservoir with the same result. So I'm making headway but it won't be solving my original issue of the pump constantly running if I have to squeeze off the supply line to get it to deactivate the pump.

 

" after I squeezed the rubber boot on the reservoir feed line to make it stop"

Squeezed, as in with pliers? = not good, that plastic hose is molded into the rubber connector, pliers could damage the line or line/connector seal.

I am thinking use the gauge on your vacuum tester to help find the leak. Hook the tester to the line running to the heater controls, then manipulate the connections to see if the pressure changes while the vacuum pump is running. Those rubber connectors get less able to seal with time, so may need to replace/hack in some new ones.
The pump will run with the key on, should turn off in about 30 seconds. Hooking the tester directly to the pump would allow you to see the range of the pressure switch, knowing this may help in determining if there is a leak.

After thought:
Those cute plastic lines with the molded rubber connectors make a "cleaner" under hood look, but could go old school and run individual rubber vacuum lines if needed.