Hello all, hate to beat a dead drum but I'm desperate, hunting season is around the corner here in Florida and I need my 4x4. I have a 2000 4x4 5.4L, I have tried everything that I know of. I've watched all the youtube videos and followed them to the T. I've replaced the actuator, both 2wd and 4wd solenoids, complete vacuum harness from solenoids to actuator, check reservoir for leaks, still not engaging. The actuator seems to move a little but not enough. I have all 4x4 lights, clicking, transfer case engages but nothing. Could this be something vacuum somewhere else? Defrost blows along with dash vents. I'm at a loss here fellas. Maybe bad parts? I've replaced both solenoids twice but from Autozone or O'Riellys. Actuator, I bought online.

 

If I understand you correctly, Vacuum is missing to operate the Actuator.
Measure the vacuum at the Actuator with the motor running.
If it's low or missing, the Actuator will not engage the front Axle.
There is a check valve and a Vacuum Can in the passenger side front fender well.
Trace it out and inspect the Can and lines.
You can also check the Actuator for operation with a hand vacuum pump.
If there is a problem with the A/C, Heat, then it's still a Vacuum issue and may be affecting the Actuator operation.
Good luck.

 

I hope this helps. On my 05 f150 fx4, the loss of vacuum is what engages the front hubs. Properly working solenoid and check valves retain the highest obtainable vacuum and disengage the front hubs to operate in 2wd. These trucks have a history of the solenoid absorbing or collecting water due to its location on the top of firewall passenger side. Your next step should be to verify that all vacuum lines are clear and free of obstruction and will allow air to pass. The next step is to investigate your actuators for water contamination.
The long and short of it is this, No vacuum and hubs will engage, as long as they were not tampered with or are damaged.

 

Just be a where, the 04 and later 4x4 does not work the same as 97 to 03 4x4 system.
The 04 and later has vacuum operated Hubs the early trucks do on use.
Single front Actuator locks up one side making the axle solid acting but for wheel traction loses...remember this is the key difference.
.
An extra to this is on vehicles that are designed to all wheel drive using external control must have a separate hub control and modulation system.
A standard 4wd would not be done full time due to steering control difficulties. Like backing into a parking spot.

 

Gene, thanks for trying to help here, but as Bluegrass says, the 4wd system on your truck is completely different than the one on 97-03. Yours uses vacuum hubs, 97-03 uses a diff lock and solid hubs. Watch this video: