Well I have a 2013 F150 FX4 and just got it back from the shop for 4wd issues. Bought my truck in January of 13 and have 10,000 miles on it. The problem occurred suddenly one morning when I left my house for work. I made it about 100 yards from my house when I heard a terrible grinding/clanking noise. Sounded like shaking metals ***** in a coffee can. At this point it had been about 4000 miles since I last used 4wd. Note: the sound would go away when put into 4wd. This quickly showed that the IWE was not holding a vacuum and was trying to engage 4wd when driving. Long story short the ford house had to replace both driver and passenger IWEs under warranty thankfully. Just aggravated since the truck is practically brand new. Has anyone else had these issues? I know this used to be a big issue on the earlier 2000 models.

 

also check solenoid up on the firewall, drivers side I believe (trace the vacuum lines, and check for holes as this is usually the problem of lost vacuum to leaks). There was a TSB were they had to install a shield to divert water/dirt that was getting in there and causing the solenoid to malfunction.

 

Have a copy of the TSB?