I know I have an IWE issue. They keep trying to engage while driving in two wheel drive. It use to be very rarely. However, it is happening a lot more now. Not sure if it is because it is cold. I have replaced the check valve and solenoid twice since November. I'm losing pressure while driving. It will bottom out and then shoot back up. It's only happening when accelerating. I have hooked a hand vacuum to the hubs and drove around. They hold pressure with no issues. I hooked up the vacuum to before the solenoid and it seemed to hold then as well. However, I cannot remember if I actually drove a while with it on. I will need to double check that option when there is no ice on the road. What I feel like is happening is a voltage issue. However, It's hard to check that, especially while driving. Not sure If can just drive for a little and then check it home while revving the engine? Not sure where or what else to check. Anybody got any tips or tricks?

 

I just had the same thing.....I didnt know this forum existed...i could have saved myself 900$ Dealer did a diagnostic (169$) to tell me what i already told them, then charged me 860$ to replace the solenoid and a check valve. Never going back to a dealer ever again.....

 

OP, it's sounding like a bad check valve to me. I'd try a YG360 valve, and make sure there is no debris in your vacuum line between the check valve and solenoid, that could keep the check valve from closing completely.
Do you have 4A?

 

I do not have 4A. I’ve replaced the check valve twice from Napa. It actually comes with a new line from the valve to the solenoid. I had to replace it a second time from breaking the valve trying to get the line off the solenoid.

https://www.napaonline.com/en/p/NOE92603901?ref=MA==

 

That looks like an OEM, the new valves look just like that.
Where did you hook up your gauge when noticing the "vacuum" fluctuating?

 

exit side of the solenoid

 

If the check valve was operating correctly, upon acceleration, vacuum should have been maintained at that spot. The blue connection is on the line coming from the engine, correct?

 

correct. I need to drive it one more time to double check. But we had ice last night and I’m waiting for it to thaw some more. The part is brand new though. Hose and all

 

Some guys have been known to get a brand new valve that was bad. If the grinding is really bad, I suggest you disconnect the power at the solenoid. This will have your IWEs engaged full time, and prevent the grinding. No, you won't be in 4X4 unless you turn the switch.
Another user, found dirt in the line between the solenoid and check valve, likely that not happening in your case, but is a consideration.
If you want, go to the parts store and buy that YG360, I've never heard of one of those bad.

 

You don't say what engine you have, the 3.5 ecoboost does not make good vacuum, it never makes pressure never should there be pressure in the IWE system only inches of vacuum. So the line to the engine should pull a max of around 20 inches of vacuum at idle, the harder you accellerate the less vaccum there is. The check valve blocks the return of vacuum to the engine from the vacuum resevoir durring accelleration. The output of the resevoir should stay close to 20 when engine is running at any accelleration level because the check valve blocks the return of vacuum if the vacuum drops significantly on the output of the resevoir or the IWE solonoid then you have a leak in a vacuum line or a leaking diaphram in one or more IWE. Vacuum at the IWE disengages them from the hub. So a leak or loss of vacuum causes the hubs to lock into the drive axels. 4WD still works because your transfer case does that, you hubs are just locked. So if you pull the line off the solonoid and cap them the hubs will be locked to the shafts and 4wd will work fine until weather is nicer for you to troubleshoot. Unless you have gone so long without repairing that you ground all the teeth off the IWE and the splines off the hubs, then you get to replace all those things. People put too much grease on the IWEs and cold weather thickens the grease and they bind and grind away. The line going to the IWE is a dual one, one has vacuum one is vented to atmosphere if the vent line is plugged with frozen water the IWE can not move as they should.