On Demand 4WD

Greeeeeeeaaaaaaaatt.

the first real snowfall we get, and my 4wd won't work...

the other day I replaced the ball joints in the rt knuckle, and the hub on the left side...

maybe it's something to do with that?

Well, kinda... all I know for sure at this point is that the vacuum solenoid for the hubs isn't passing vacuum down to the knuckles (like it would matter, I changed over to Warn lockouts when I got the truck)...

so I start reading the diagnostic tree... good Gawd... Ford wants me to test the GEM module with a NGS tester... whatever happened to "...measure voltage at pin A; if more than 10v go to step 25, if less then 10v, go to step 49..."

a couple calls to local dealerships revealed that neither of them stock the servo motor, nor the dash switch (my first two non-diagnostic guesses), which I've found over the years is a pretty good indication that particular part has very low failure rates...

it did begin to work for a short time (untill my dumbass flipped the switch back to 2wd mode), and when it did, the heater lost vacuum and defaulted to defrost only (my clue about the vacuum solenoid)..

I'm up for tips if anyone else has had 4WD problems and fixed them; other than that, I'll keep you posted...

JLDickmon said:

... I changed over to Warn lockouts when I got the truck...

...it did begin to work for a short time (untill my dumbass flipped the switch back to 2wd mode), and when it did, the heater lost vacuum and defaulted to defrost only ....

Click to expand...

If you removed the SOTF front factory lockouts with Warns, why not unplug the vacume line that goes to the solenoid? You don't need the vacume anymore if you have Warn manual hubs. Unplug the supply line from the vacume reservoir and plug the port with a vacume plug. At least that will take care of the air coming out of the defrosters only problem.

I did that myself when I put manual lockouts on, haven't had a problem since. FWIW, I have pics of the SOTF to manual lockout conversion including removing & plugging the vacume port at the reservoir in my webshots, link is below.

Tail_Gunner said:

If you removed the SOTF front factory lockouts with Warns, why not unplug the vacume line that goes to the solenoid? You don't need the vacume anymore if you have Warn manual hubs. Unplug the supply line from the vacume reservoir and plug the port with a vacume plug. At least that will take care of the air coming out of the defrosters only problem.

I did that myself when I put manual lockouts on, haven't had a problem since. FWIW, I have pics of the SOTF to manual lockout conversion including removing & plugging the vacume port at the reservoir in my webshots, link is below.

Click to expand...

well basically, with the solenoid currently stuck in "block" position, that's what I've got.

why didn't I remove and plug the line earlier? that would require a little thing called "effort"

anyway... I can't understand what the vacuum solenoid has to do with the GEM module, unless it's position is an input...

OK... here's what happened today...

kid borrowed my truck to go get hay... she said the 4WD was kicking in and out, and when it did, the heater would switch to defrost..

when she got back with it, I whipped it in the shop and decided to power the red wire from the POV solenoid to the GEM... well, of course it didn't work.

AAAAAAAAnnnnddddd.... when I went to back the truck out of the shop, it was hung in reverse and a drive gear compliments of the PCM... soooo..

I had a spare GEM and swapped it in... no difference...

called Ford, got a range switch (park-neutral switch, neutral safety switch, whatever you want to call it)...

HEY.. now I can drive home...

4WD still don't work, but minor details..

IT"S FIXED

swapped the other GEM back in...

here's the biggest PITA...

I need to update my MODIS so it does GEM codes & data.... I got shown up by a Mac Determinator...