Front 4wd seems to want to engage during early driving.

[Will Cunningham]

My 2016 Expedition 4wd seems to want to engage and 'growl' when first driving and turning. Sound mostly on the front drivers side, but have not had someone listen on the passenger side. I have replaced both IWEs and vacuum solenoid and hoses. Checked the vacuum on both IWEs per the Technical Service Bulletins and they check out with no vacuum loss over even a 3 minute test. 4wd engages and disengages properly, so think my switch is good. Tested the vacuum both in 4wd and out with proper results. I have not replaced the long hoses to the IWE since there did not seems to be any vacuum leak during testing on the hose or IWE.

Baffles me since it sounds a lot like the noises of 4wd engagement I heard prior to IWE replacements. The problem seems a lot less after I have driven for 5-10 minutes, but not always. If I drive straight ahead for several hundred feet before turning like at at traffic light before I turn, there is usually no problem. My guess is insufficient vacuum at times, but my test results do not indicate that. Suggestions appreciated and solutions would be great!!!

Thanks in advance!!!

 

[Trainmaster]

Sure it's not a wheel bearing? Sounds like you have the IWE system pretty well covered.

 

[Will Cunningham]

Wheel bearings are good. Noise is almost always when turning when I first start up. Only 93,000 miles on it and checked bearings when I replaced the IWEs on both sides.

 

[Trainmaster]

It sounds like you know how these things work. If the IWEs aren't releasing on start up, they're not getting sufficient vacuum or they are sticking. Lift the front end, remove the hoses and check the lock/unlock response qualities with a hand-held vacuum pump while spinning the wheel. Then check the vacuum source with a gauge. You have to narrow this down and that's the only way I can think of doing this.

My experience with IWEs is nothing but bad with aftermarket parts, for what it's worth. I never had a problem with Motorcraft parts though and these things are usually pretty robust.

 

[ExplorerTom]

I had a similar issue.

Jacked it up, removed the wheels, started it, shifted in/out of 4wd, used a vacuum pump/gauge……. Everything pointed to the system working fine. But still had the noise.

Installed the RCV lockouts- no more noise.

And oh by the way, I’ve recorded several 16+ mpg tanks since then. So if there’s an effect on mileage, it’s minimal.

But the front end components aren’t designed to spin 100% of the time….. the front diff is a Ford 8.8. Same axle (center section) as the rear axle they used in Explorers/Rangers. Now the data is still out on those since they only made a couple dozen of those, but I think it’ll be fine. And the front CV axles- FWD vehicles aren’t a new thing either. True, maybe the CVs will wear out faster.

 

[ediddily]

Since you replaced solenoid, main hose (main hose should include short hoses to hubs) and iwe's and bearings are fine, did you check or think about replacing the vacuum storage box?
My 07 XLT had a vacuum leak for the longest time. I eventually replaced everything and I mean everything: solenoid, upperhose contraption, lower hose, vacuumstorage box, and IWEs; now its been solid and reliable. If you opt for aftermarket no name brand IWEs like me, sometimes they don't last very long and others are great.
But noise sounds like mine did in a sense i.e. minor vacuum loss over time and IWEs slowly release at certain RPMs. Also a good idea to double check wheel bearings. Another thought is, like mine, time to rebuild front differential.
Recently we went camping towing our 6k lb trailer for 3hrs and only after everything is heated up after driving and we start to slow down and brakes applied we started hearing thumping and grinding up front. My suspicion is a differential bearing is on its way out and since changing the oil up there is difficult I never have after 150k under my ownership.
So my plan soon is to pull it out, have it rebuilt, and put a lunchbox locker in.

 

[twodollars]

8.8 center section has been around a long time, plenty robust if its spinning all the time. Will only transfer power with t case engaged, so actual load in 2wd would be minimal.

 

[ediddily]

In my experience power is distributed:
2wd= hubs unlocked via constant vacuum
4wd= hubs locked via spring engagement without vacuum
4auto= front hubs unlocked (2wd) unless TCS detects difference in spinning rate between front and rear wheels then releases vacuum to lock hubs then once corrected unlocks hubs again.

The front differential and shafts are always spinning.

 

[Will Cunningham]

UPDATE

All parts are Ford OEM.

Replaced vaccum lines from solenoid down to both wheels with Ford Part FL1Z-7A785-A 1x

Here are the tests I ran: Note that all tests started with 20 pounds of vacuum.
1. Passenger side IWE cycled fine( engaged and released with CV axle turning or disengaged using vacuum pump). 2 minutes test of vacuum using mini vac hand vacuum pump. Large hose bib dropped 1/2 pound in 2 minutes and small hose 1 1/2 pounds
Driver side IWE cycled fine with and without vacuum from mini vac hand vacuum pump .Big hose bib did not show any vacuum drop in 2 minutes and small had 1/2 pound drop in two minutes.
2. O pound vacuum drop at hose checked before the check valve in 2 minutes at solenoid
3. 0 vacuum drop from hose near check valve to vacuum tank in 2 1/2 minutes(Note- hose was disconnected from check valve.)
4. Large vacuum line disconnected from check valve near solenoid had 10 pound drop in vacuum during the first minute and dropped to zero at 2 1/2 minutes. I think this is the 'supply' side fro vacuum from the engine and the vacuum drop was expected. Correct me if this in not what I should see.

I checked vacuum hoses at the IWEs with the engine running. Results were 25-28 pounds at both IWEs.

Looks like all should check out, but still getting the intermittent sound that IWE is engaging (Drivers side) when turning and engine rpm is lower. Thinking about just unhooking the IWE hoses to see if the noise continues. My thought is the IWEs will be engaged, so should not make any sound. I know there will be some wheel slip when turning on the front tires.

Pretty baffling, so would love to hear solutions. Will post results after I check with the IWE disconnected or 4wd engaged.

 

[Will Cunningham]

Problem solved after I replaced both wheel hub assemblies. Still a little noise when turning, but think it is just tires scooting a little. Deep tread and new tires. Along the way, did find and repair several other defective parts. Figured the parts needing replaced were probably worn due to the hubs needing replaced.
The weird thing is that the hubs did not sound like most I have replaced over the years and did not have any play when testing with the wheel for movement.
Thanks again for all of the suggestions.