That's pretty much what I understand as well. Of course the more vacuum, the merrier.

 

Manifold vacuum can easily stay well above that just cruising.

 

I just seen that the TSB only stated that the fix was for the AWD/Torque on demand trucks, not the Part Time 4WD trucks. Didn't know if Ford was doing something else for the part time 4WD systems.

 

What I understand, is the TOD system engages the TC before IWE lockin, to bring everything up to speed, it does it thru the TCCM. That's what I've been led to believe. On the ESOF, I don't know for sure if both things happen at the same time, or one after the other. I'm trying to find out, but haven't found that info yet.
After having said all that, I don't know why the difference for sure.

 

You may be absolutely correct on that which is why I thought earlier that the TSB eliminating the vacuum system for the actuators wouldn't affect gas milage if the transfer case TC wasn't already engaged but nobody answered that question for me. I don't know how the TC becomes shifted or if it's engaged permanently. I had only studied the function of the actuators. I don't have 4WD myself but I became interested in this problem.

I should have stared that the wheels alone become engaged for 4WD operation realizing what you just pointed. People had been asking if gas mileage would be affected by the TSB. I'm inclined to think not but yes if the TC was permanently engaged.

 

Here is what they did to mine today. Covered under power train warranty. Vacuum caps. Also washed for me. It’s a good day!

 

You're the first here I know of that had done, congrats, I think.
Did you notice any heaviness in the steering? Don't know if you pay much attention to mileage, but if you do, please let us know if it was affected.

 

I have only had it 3 weeks with a 36 gallon tank. I won’t have a good history to go off of. I didn’t notice any difference in the drive home.

 

Oh well, likely be some others that'll be done to. I asked about the steering because on my '17 with the 3.5 Eco, I could feel a slight difference when the IWEs pulled out after the warmup cycle. It felt a little lighter.

 

I bought a 50K mile 2017 Lariat ecoboost Screw in August. After getting the VCT repaired, we immediately left on a 6,000 mile cross country trip. I discovered that the tech forgot to plug in the IWE solenoid about 1/4 of the way through the trip. After plugging in the solenoid, I heard the IWEs grinding a few times in the mountains of North Carolina and again in town and on the freeway in Missouri.

I complained to the selling dealer when I got home. They said they couldn’t duplicate the problem. A few weeks later I was loading my motorcycle in the back and then tried to back up the little ledge I had dropped off to get back on my gravel driveway and 4 wheel drive was not functioning at all. I gave a video to the dealer service writer and they took the truck in for repairs. They replaced the IWEs and wheel bearings and the seals. I haven’t verified if they just disconnected the vacuum line or not.