Grinding / scratching front end noise during acceleration which can be not IWE

[ftp19601960]

I experience some grinding / uneven scratching noise seemingly coming from some front/middle point on my '17 4WD XLT during acceleration. Initially I thought about one IWE (it's a 'mono' sound). The mode switch 2H/4A changes nothing. I believe 4A shall cut off vacuum completely out of IWEs and those must be engaged all the time. And it comes from the middle not from any side. Can it be PTU itself?

 

[99WhiteC5Coupe]

I experience some grinding / uneven scratching noise seemingly coming from some front/middle point on my '17 4WD XLT during acceleration. Initially I thought about one IWE (it's a 'mono' sound). The mode switch 2H/4A changes nothing. I believe 4A shall cut off vacuum completely out of IWEs and those must be engaged all the time. And it comes from the middle not from any side. Can it be PTU itself?

The IWE vacuum check valve and/or the IWE vacuum solenoid may be defective or leaking (or their connections).

If so, the vacuum to the front IWE hubs may not be consistent, causing the noise.

Some time ago, Ford issued a TSB instructing dealers to replace the IWE vacuum check valve (and not to test it) - if the grinding noise was heard. It is very easy to replace.

When accelerating, the engine vacuum can drop - causing intermittent IWE engagement.

 

[ftp19601960]

That's why I always stay in 4A (instead of using permanent caps as latest TSB suggests). 4A is supposed to cut off vacuum and keep IWEs engaged all the time. The grinding remains though.

 

[ediddily]

Mine had a minor leak somewhere which went away with high rpms. Your IWE can also develop leaks. Or perhaps, its time to rebuild the front differential.
And for clarification:
2wd=hubs unlocked through constant vacuum
4wd=hubs locked without vacuum
4auto=hubs unlocked until TCS detects front wheels spinning out of sync and releases vacuum as needed to lock hubs and unlock when corrected.
I only know this from trying to pass a car on a icy 2 lane mountain road in 4auto. I accelerated hard to pass and the rear end slipped out freaking me out then I hear a loud CLUNCK as I was still steering to correct and the front end grabbed and corrected.
Its a horrible design, but the front drive train is always turning, even in 2wd, if you dont believe me, put the car on jacks and idle in 2wd, you will see and raise your eyebrow like Dwain Johnson.