IWE Vacuum will not cut off in 4WD mode

[Brian Dallas]

Hello all. Simple question I am sure but I am having an odd IWE issue. Here is some of what I have experienced.

1. When going into 4WD H or L I am getting an intermittent bang under load. Almost sounds like the IWE is partially engaging.
2. There is an intact vacuum set up as the hubs are free spinning when the truck is in 2WD. Turn the truck off and the axels are engaged.
3. Turn on 4WD H when the truck is running with the wheels jacked up, axels spin freely forward and back.

I am thinking the the solenoid is not releasing vacuum pressure when the truck is on, but it when it is powered off since their is no vacuum to be had from the engine.

Could this just be a bad solenoid or check value?

Any help would be appreciated.

 

[TomDirt]

Do you have access to a mityvac to test vacuum on the system? That's a quick & easy way to start checking out the vacuum lines, the IWE themselves, & the check valve. The vacuum reservoir should hold vacuum for awhile after shutting off the motor too. There's lots of youtube videos to walk you through testing it all. The solenoid probably won't be loud enough to check with the motor running, though.

 

[fordfreek]

Could be a bad solenoid I guess. The solenoid is energized to send vacuum to the iwe's, so either it's mechanically not venting when it should, or it's not being turned off electrically when selecting 4wd. Check valve just keeps the vacuum from being bled off under no/low vacuum times. I wouldn't suspect that as the cause. Check valve failure usually lets the vacuum off when it shouldn't, causing unwanted iwe engagement in 2wd.

 

[TomDirt]

Whatever you do, get it figured out before you have to replace both IWE's. At that point, either you:

 A, spend a hundred bucks and commit to a greasy, time-consuming repair yourself,
 B, hand over $400 to an independent shop who might or might not do it right, or
 C, hand over $800 to the stealership.

 

[rschap1]

It usually takes me a little bit of investigating (most often posting a few questions here too) before I actually get to the real issue.
None of my IWE troubles made much sense when I first start looking.