First time posting here, been lurking for a while but this is my first time having a problem on the truck. Looking for some veteran advice before I go blindly replacing parts on the truck and spending unnecessary money.

Truck is a '14 FX4, 51k miles.

I did a leveling kit last year on it around 45k miles, and went with bigger wheels and tires at the time. Shortly afterward, I noticed a weird occasional rattling/grinding that went away after it did it a few times. Gas mileage started to go down...I expected some drop with the bigger tires, but this seemed more dramatic. I do get some road noise, but wasn't sure if it was indicative of a problem or if it was just common tire noise from the bigger tires.

I've been reading a lot of IWE posts which lead me to start down that path, but nothing that had clear cut answers that I could find. I did a quick test this morning and found the following:

(with the truck running)
Driver side 2wd: Tire spins freely, axle doesn't move.
Driver side 4wd: Tire and axle are locked together and don't move.
Passenger side 2wd: Tire and axle spin together.
Passenger side 4wd: Tire and axle are locked together and don't move.

From what I understand, there are 3 main components to this system...the IWE's themselves, the vacuum lines, and the solenoid/actuator on the firewall.

The fact that the driver side seems to functioning fine leads me to believe that the solenoid/actuator is working as it should. I don't notice any noticeable visual issues with the passenger side vacuum line, although I only traced it just past the top of the shock tower. I did order a vacuum pump test kit on Amazon that should be here tomorrow. Does anyone know how much vacuum it should be pulling in idle at the IWE connection?

Am I safe in assuming that if I have good vacuum at the IWE connector, it's the IWE that is the problem? If I'm replacing the IWE, should I go ahead and replace the hub too while I'm in there (since it has 51k on it at this point)?

Any other seasoned recommendations? Thanks in advance for any help!

 

If you have good vacuum at the IWE then it means that you have a leaky IWE unit and its stuck in the lock position.

Both IWE engage when vacuum is removed and disengage when vacuum is applied.

I wouldn't change the hub/bearing if the locking gears and/or bearing is still tight since changing the hub unit is relatively easy and not time consuming.

Cheers!

 

There is also a check valve between the solenoid and the IWEs themselves. It is known to work intermittently and replacing it has resolved a lot of people's IWE issues.

Also, you could have a plugged line going to the passenger side preventing vacuum from disengaging that side.

However, it could be the IWE as well like you say.

Just some other things to check.

 

Did you install it yourself? The grinding is the IWE not lined up, and if the grinding is bad enough, it won’t repair itself. When I did mine, it got replaced incorrectly and would only correct itself when put into 4. So I would check if they are aligned, they didn’t have to replace my hub, but all the work done equaled over 700.

 

I went through this with the exact same symptoms. It did turn out to be the IWE actuator. If you have a vacuum pump handy you can apply and remove vacuum right at the actuator connector to verify it. You'll put it on the larger of the two connectors. The smaller one is just a vent. I have heard of guys being able to test them by just putting a vacuum hose on the fitting and sucking on it with their mouths, but I don't suck that much. When vacuum is applied however, the wheel should spin freely without the drive axle turning.

The local Ford dealer quoted me 166.00 for a new one (part only) so I went with the Dorman version on Amazon which was less than half that. (Dorman 600-105 4WD Locking Hub Actuator). Dorman offers a great warranty and they were virtually indistinguishable from the Ford originals. At that price I went ahead and did both sides. They have been working great.



Replacement is not that difficult and should take 30min or so. FordTechMakuloco does some great videos on both diagnosing and replacing them. In my case, the solenoid is actually on the driver side by the brake booster.

 

Thanks for the information everyone! My vacuum test kit just got here (thankful for Amazon 1 day shipping), so when the rain stops, I'm going to go do some testing. Will report back what I find!

 

Ok, so here's what I've got...

Driver side (working, tested at the IWE connection):
2wd: 26" vacuum
4wd: 0" vacuum

This is what I expected to find.

Passenger side (not working, tested at the IWE connection):
2wd: 26" vacuum
4wd: 0" vacuum

So it seems all of the lines and check valves are in good shape and the actuator is working. Looks like I'll be ordering an IWE this week.

Wanted to post these numbers in case anyone stumbles across this in the future.