I have the EFOF I decided to check it out and when I turn my switch to 4X4 my transfer case engages and my light comes on. I had my heater on and was on high and then it went to defrost and stayed that way for about 30 seconds and then went back to heater. I put the truck in neutral set the parking brake and got under my truck and tried to spin the front drive shaft and could not so I know my hubs are locking in. I even was under the truck and had someone to shift my 4X4 on and the drive shaft locked up as soon as the switch was turned so I know it is working. My heater would stay blowing on high after it came back from defrost so I don't think I have a vacuum leak but I just wonder if I have a weak pump? I have tried shifting my 4X4 several time and it always dose the same thing, after about 30 seconds it would default to defrost then 30 seconds back to heater.

 

Ford put some very cheezy vacuum hoses on these trucks.Check the hoses from the vac pump to the hubs.I bet you have a vac leak.Could be the solonoid as well.I had to change mine on my 02....God luck to ya

 

Like Barry said, you have a leak, somewhere. Probably at one of your hubs. It's not going to be obvious with what you have described, but it is there.

 

When you put the switch in 4x4 it sends power to the motor on the transfer case to shift. It also sends a signal to the solenoid to start vacuum to lock the hubs. Just because you can't turn the front drive shaft by hand, don't mean the hubs are locked. It means the transfer case is engaged. Sounds like the guys have you on the right path with there being a leak somewhere.

 

How hard is it to change the hoses to the front hubs. I really don't think I have a vacuum leak but I will take a look at them.

 

You could always jack the front wheels off the ground, engage your ESOF and see if you can turn the wheels. At least you will know if your hubs are engaging. The defrost thing still makes me think you got a small leak somewhere.

 

Easier than filling up your fuel tank.

 

I am confussed, if I have a vacumm leak wouldn't my defroster stay on?

 

i have the same exact thing. i noticed that when i lock my hubs in and put the 4x4 on it works fine and the ac wont blow off different ways. try that. i am going to redo the vacuum lines this weekend.

 

Nope. IIRC it doesn't maintain vacuum to the hubs, it just sends a command for xx seconds to activate the hubs. If your HVAC is defaulting to defrost, you've got a leak. Remember, you have a vacuum accumulator too, that has a big reservoir. That big oval thing behind the passenger side battery is a tank filled with vacuum (is that possible), so that means when you shift to 4x4 your emptying that entire accumulator. I'd say a pretty BIG leak.

 

Hmmmmmmmmmmmmm After the defroster comes on for about 30 seconds it will go back to heater and stay at heater, I left it in 4X4 4 about an hour and the heater stayed on. When you shift to 4X4 vacuum locks the hubs, what keeps the hubs locked in and what unlocks the hubs when you go back to 2X4? Trying to understand how this thing works.

 

Well I was going to get the verbiage from the manual, but can't find it right off. The magic is done by the Pulse vacuum hublock (PVH) solenoid though. It's a solid state device that activates and deactivates the hubs.

 

I understand what activates the hubs but inside the hub when the vacuum dose it's magic, in other words how do the hubs work when I turn the switch. If vacuum is applied to the hubs to engage them then there would be vacuum to the hubs untill I put it back into 2 wheel drive, am I correct?

 

It's been so long since I had to work on mine, before I stick my foot in it, I'll scour through the manual and find it. Here's what I remember, basically there are two different mechanisms on the hubs for activation. Manual, turns the **** on the outside, this engages, or disengages. The other mechanism is the back side of the hub. It has a plunger assembly that when cycled, will ratchet the hub "on", when cycled again will ratchet the hub "off". But I'll find it unless someone else chimes in.

 

Well I have discovered that my hubs are not locking in as yesterday we were having a pretty good amount of snow and the roads were covered. So I manualy locked in my hubs and turned the switch to 4X4 and the light came on and I heard the transfer case engage. Pulled out the drive and got stuck, friend said front wheels were not spinning sooooooooooooooooo now I was going to replace my hubs with Warn #11690 but Warn says they will not fit dual wheel application, I wonder why they won't.