Hey guys,

First post here, I had been reading around trying to find out my issue but nobody seems to have the exact same problem as I do. I have 2005 FX4 with the 5.4.

So to start off with, my 4wd does not work properly whatsoever. Shift it into 4wh, hear a click but no dash light and no obvious front wheel power. Shift it to 4wL, light comes on, audible clicks are heard, the gear ratio changes, but once again no obvious front wheel power. What I mean is that turning sharply and giving throttle does not cause the classic 4wd "lurch" forward. But my (albeit minimal) diagnostics have me stumped.

First of all, the front driveshaft DOES lock and unlock. Put it in either 4wh or low and you cannot spin it by hand, back in 2wd and it free spins again. Also as stated you can hear the TCase click when engaged into either, and i believe I can also hear a click from the front in 4wL

So any thoughts onto both a.) why the 4wH light will not engage (turns on at startup and occasionally flashes when attempting to engage), and why in both the front wheels do not seem to have power? Any help would be appreciated. It does not seem to fit the bill for either a vacuum leak in the front or a failed TCase solenoid/motor in the rear so i am honestly lost. Haven't attempted to remove the vacuum from the front end yet, will do so when I'm home from school this weekend to see if it locks the wheels properly. I just have my doubts as it seems the front solenoid usually fails the other way i.e the wheels are stuck locked in.

 

Sounds like a IWE problem and possibly an old style IWE solenoid... need a vacuum pump to troubleshoot.

 

yeah I could believe that. From reading on here though it seems as when the solenoid fails it usually sticks closed? Also since it seems my issue is the wheels will NOT lock, would I need a pump? I was under the assumption removing vacuum will lock the wheels, not adding

 

You are correct that a lack of vacuum should cause the hubs to lock. The easy way to check this is jack the front off the ground and with the engine off the front axle shafts should spin with the wheels.
If you have 1 messed up hub you will get no drive from the front axle though, since it's an open diff the axle with the least resistance will just spin and if 1 hub isn't engaged that is the one that will just spin on the axle side...

 

haha well this must be a double problem. Just got a replacement solenoid (new part number) and 4 wheel high light now works again! But there still seems no difference in either 4wd. In low I can hear the high pitched hum that I’ve always associated with it, but the front end won’t “bind” on a dry pavement when turning. Occasionally at around 10 mph it will.

Does the FX4 have an open diff in the front end for the 05? I thought it was a LSD. This is the first time I’ve dove into drivetrain issues on a vehicle (besides the transmission I replaced on this same truck) so I’m pretty ignorant to a lot of this information, apologize in advance!