I pulled the vacuum lines off of each of the IWE units at each wheel. Placed the transfer case in 4x4 and checked to see if the front shaft was turning. It was locked in, but the wheels each turned freely with NO vacuum going to either side. Is this a clear indication that both IWE's have failed and need to be replaced? If so, are they a dealer item only?
I also checked for vacuum at each wheel with the selector in 2x4 and found vacuum. When I went to 4x4 the vacuum stopped at each wheel, which should indicate that the solenoid is working.

 

Check out this thread. It has everything you need to know about diagnosing and replacing the IWE along with part numbers.

https://www.f150online.com/forums/ar...replacing.html

 

vacum keeps the front axle shafts disengaged. no vacum locks in the axles. its done this way so if you lose vacum you will still have 4x4. a good way to check the vacum system is raise the front wheels, start the truck switch in 2wd position. the spin each wheel by hand and the axles shouldnt move. switch to 4x4 and the axles should spin with the wheel. switch back to 2wd and check to see if axles disengaged from wheels. also if you have a hand vacum pump with a gauge, disconnect the vacum lines at the knuckle, vacum test the hub. it should hold vacum until you release it. check both wheels.

 

Hi All,

I just started having the same problem. The sound on mine was coming from the left front, and I had replaced the brakes a while back and thought I screwed something up. I didnt.

First of all one other responder stated that vacuum is required to keep the truck in 2wd He is right on with this. I put my truck on jackstands all around to analyize the problem, and in 2wd with truck running you can spin the front rotors. Kill the engine, vacuum bleeds off, and you cant turn the rotors. I am not sure if this is normal, but thats what happened to me. Vacuum on 2wd. Vacuum off, 4wd. Why ford did this I have no idea.

The IWE solenoid that is mounted on the firewall right behind the battery is located right where water running down the gutter from the windshield will cascade onto it. Way to go ford. There is a small two pronged plug that sticks into the front of the solenoid. Mine was badly corroded. I cleaned the blades in the male plug with a finger nail file, then sprayed both plugs with electronic cleaner. I also sprayed some cleaner into the air ports on the solenoid, and cleaned the rubber connectors. I re-installed the solinoid, and made up a cover out of some uncured rubber roof flashing to redirect water away from the solinoid. There is also a large four pronged plug mounted to the firewall which is also in harms way. I cleaned that up too. Not sure if that applies but what the heck, I was in there right?

This solved my problem. I ordered a replacement solenoid on line for around 16 bucks (The ford dealer I bought the truck from wanted $54 dollars plus tax. Three times as much for the same damn part)

What I did notice when I had the truck up on stands and I put it in 2 wd out of 4wd was a pretty loud clunk, like something had been hanging up for a long time that I never heard before, so I do not think that this truck was ever right from the day I bought it.

It seems to be fine now, but we shall see. Frankly, I dont know what was wrong with getting out and locking the hubs when you want dig and chew, but I guess this is what they call progress. Considering the fact that vacuum is needed to keep it in 2wd, we are going to see a lot of this type of problem as rubber vacuum lines age, and crack. This is really a stupid design to my way of thinking, but so was the spark plug thing.

 

If you used the link and read the great posts by TNF150, you've probably figured out by now that your IWE's are bad. The good news is that the replacement of them is pretty straight forward. I have access to a shop with a lift and pretty much any tools I need. Never having done the job before, but using TNF150's guide, two of us knocked off both IWE's in less than an hour. (And you do not have to pull the half shafts.) Have fun!

 

https://www.f150online.com/forums/ar...then-some.html

use the steps provided on the first page in the link i provided above to test the vacuum system.