I've been having this issue for over a year now. While in 4A or 4H, I get a grinding noise while accelerating. most noticeable between 10 to 30 mph. I took it to the dealer, and they replaced the hubs/actuators on both sides. The noise was still present after their first attempt, they "reinstalled" them and the noise went away. I challenged them as to why those parts failed and if they diagnosed the root cause, they assured me everything is working as it should.

I rarely use 4wd, yesterday I turned it on and the noise returned.

From what I read about the IWE system, most people have an issue with it keeping vacuum, and hear noises while in 2wd. I have the opposite issue.

Could this be vacuum related? Is it possible while in 4wd, there is still vacuum in the system causing the hub/actuators not to properly engage? Is that a solenoid or a check valve issue?

What other causes could there be?

2013 f150 Lariat 4x4

 

I have a 2018 now but my previous truck was a 2013...and yes it could be a checkvalve issue as it sounds like your actuators aren't getting the full vacuum.
Normally tho you are right as generally the grinding sound goes away when in 4wd
Also, check the vacuum lines that go down to the IWEs inside the wheel well.

Ford attaches them to the spindle and eveytime you turn your steering they get pulled in either direction.
After a while the lines will crack near to where they are attached and lose vacuum...this was what happened to my truck.

 

Don't I want them to get no vacuum? I dont have any issues in 2WD when there is suppose to be vacuum

 

Yes thats correct, no vacuum means 4wd...but there shouldn't be noise when in 4wd.
The only other thing I can think of is the IWE is not engaging...something is preventing it from engaging be it the hub or the IWE itself.

 

Could also be the front diff and/or transfer case. Doubt it is the actual IWE now unless the dealer screwed up the install.

One way to find out since it doesn’t happen in 2WD is to get a vacuum pump. Apply vacuum (7#) to the IWEs. Plug the source vacuum line so as to not get dirt in the system, put the truck in 4WD and see if the noise is still there. Be sure to strap you vacuum down so it stays put while you drive it around. If the noise is still there, it isn’t the IWEs but, something else like I suggested above. If it isn’t then the IWEs aren’t fully engaging.

 

To add if it turns out to be the IWEs again, about a year or so ago it was reported that the new IWEs were coming with to much grease in them. This could hinder or slow the engagement. Some grease had to be removed to get them to work properly.

 

Thanks. That would be an interesting test - but do I need a vacuum pump? I thought I want no vacuum for 4wd. Could I just unplug it at the solenoid (pluggin the source) and see how that goes in 4WD? The vacuum shouldnt be doing anything in 4wd correct?

 

By applying vacuum you are disengaging the IWEs so that only the other parts of the 4wd are in operation. You technically won’t be in 4WD since you are applying vacuum via a different source. Thus the need for a vacuum pump. This will take the IWEs out of the equation when in 4WD. It will either rule them in or out as the cause of the noise.

 

I get it now. If the noise is still there I know its not the IWE's.

Is there a pump that you would recommend? I dont want to break anything else!

 

People here have used the one at Harbor Freight. Just don’t put more than 7# as that is all that is needed to fully disengage the IWEs. I’m sure there is a little leeway on the amount of pressure but, don’t go much past 7.