Is there a way to check the vacuum on the 4wd system? I replaced the iwe solenoid but it is still not engaging. Lights are working now on the dash. Want to check the vacuum before replacing the motor on the transfer case. '06 with the 5.4L. Thanks

 

I would check out this video. Very informative on 4WD testing.
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Remember that the IWE system uses vacuum to disengage the hubs. No vacuum = 4x4 and hubs engaged. Vacuum = 2wd

Jack both front wheels off the ground. With the engine off both front hubs and cv shafts should engage. If one does not then that side has:
a) a bad IWE actuator
b) stripped splines on the outboard part of the axle shaft where it engages with the IWE
c) the 13 mm nut on the axle is loose, the axle has 'walked in' so that its splines do not engage with the IWE

To check for 2wd operation get a handheld vacuum pump with a gauge. Pop the vacuum line off of each IWE actuator. Vacuum test the IWE/hub side. With vacuum the IWE should disengage the hub from the shaft. If it does then spin the hub and make sure vacuum does not leak down. Prove both sides good. Then check for vacuum when in 2wd via the vacuum harness.

Happy hunting

 

Thanks guys. This helped a lot. My passenger side actuator is bad.