Originally Posted by johnday

Yes, whenever the engine is off, the system will vent off vacuum at the solenoid, locking in the IWE. By turning the key like you were, likely did as you thought, depleted the vacuum reservoir.

With the GENII 3.5, Ford went to a different vacuum setup, no pump, it appears to be a venturi tube setup, called "ActiVac". I haven't been able to find a lot of info on it. I could be 100% wrong here, so don't quote me as fact. I "think", vacuum is supplied as normal from the intake, when you go into a boost condition, I "think" manifold pressure/flow, is routed thru a venturi, [ejector/eductor whatever you want to call it], and provides vacuum.
Anyone reading that, if you know more, please post.

No one take as gospel what I just described!!!!!!!!

Originally Posted by Wicked ace

Not a bad description at all.It is a modified jet pump that causes a low pressure area causing a pressure drop across a venturi. But I think it is a supplemental system controlled by the ECM as a pressurized engine isn't good at creating vacuum.

Originally Posted by johnday

IIRC, the TCCM is mounted in the cab down below the glovebox. No reason for anyone to be doing anything in that area when doing your level.
If you have a DVOM, you could check the connector on the top of the solenoid. It has a switched ground, so, with truck running in 2WD, you should have power between both connectors. Have someone switch to 4A/4H or 4L, doesn't matter which and you should loose power. "If", you do loose power, your TCCM is giving a signal to open the vent and close off vacuum. "If", you do have power in 2WD, I'd probably replace the solenoid with an OEM part, not expensive, but use OEM, there's been a number of guys replacing with Dorman brand, and still have problem.

Originally Posted by Bassman150

I seem to have a similar problem. When in 2wd I have no vacuum. I changed out the solenoid with a new one, same problem. Test voltage and get 4.5v across the solenoid with truck off, no change with truck engine on, still 4.5v. I believe it should drop to 0v to close the circuit. correct?
When I bypass the solenoid by connecting vacuum supply with the vacuum feed to hub (connect to hoses together), magic and all good, nice free wheeling with both front tires. However, now no 4x4 ability because of vacuum engaged. Just trying figure out if it is a second bad solenoid or TCCM issue? Thoughts?

Originally Posted by blue2010xlt

Have you checked or replaced the check valve?

Originally Posted by johnday

I'll check mine in the morning, but having power with the key off doesn't sound right.
Are you checking with using the connector, power to ground, or from the connector to an external ground somewhere?

Originally Posted by johnday

I'll check mine in the morning, but having power with the key off doesn't sound right.
Are you checking with using the connector, power to ground, or from the connector to an external ground somewhere?

Originally Posted by Bassman150

I'm checking between the two points right on the connector. There is a 4.5 volt potential different the two points.... I though I would see a drop in voltage. That said, it is an open circuit as I have the solenoid removed during the measurement. Maybe introduced my own problem.

Originally Posted by johnday

OK, just checked mine. With key off, I showed, 4.5 volts, power to ground through the connector. With engine running, 14.5 volts. Switched to 4H, 4.5 volts.