Alright ladies and gents, i need some help here. I am having a 4wd issue. Here are the symptoms and what i have checked.

The truck is a '98 f150 lariat, 5.4L (has the 4wd **** switch)

It will not engage. I will select 4H, the light in the cluster will not come on (i tried doing this in P, R, N, D, 2, & 1, nothing) then I will go to Neutral and select 4L, nothing happens, no light.

I got under the truck, had someone select 4H as i watched the vacuum motor on the front diff, does not move. I then took off the blue vacuum line, no vacuum. i then had them put it back in 2wd. Took off the other line on the motor, good vacuum there. Had them select 4H again with that same line off, vacuum still is there. same thing in 4L.

The vacuum should switch between the two lines when selecting between 2wd and 4wd, correct? Also, i hear a "clicking" noise behind the cluster when i turn the truck on (does about 3-4 clicks) and it did it again when we went back to 2wd (only does it once and will do it again when you shut off the truck then turn back on).

Where should i go from here? I am about to go check for some fuses to see if any are blown, which i am not familiar with fords at all. I was thinking that the 4wd solenoid was bad, but since i am getting constant vacuum in the one line (not the blue one which is the 4wd vacuum line) it is throwing me off.

Help me out guys and gals!

 

if your getting vacuum at solenoids under the hood but no vacuum down to the diff that would be the first step. with my other truck my 4wd never worked. the transfer case shift work waas seized so i had to fix that. after that i changed the diff fluid and sprayed some wd40 on the actuator shaft on the diff. it would pop in and out than it started to work strangely

 

Just went back out and checked vacuum at the solenoids. I am getting constant vacuum out of the bottom lines on each one, in both 2wd and 4wd. Checked any fuses that would have to do with it (fuse 23 in the inside fuse box) and it was good.

 

Cracked line down to diff possibly

 

I am about to go out and check the blue vacuum line for a break. I am sure the switch is working. When i go to 4L i can hear it switch to low-gearing in the tranny.

 

The lines going down to the diff are good. I am hearing the resistors click behind the dash when i move the selector switch around, but the lights do not come on.

 

The solenoids are good right? I have never had to deal with this issue.

 

Pull the inner fuse box and check for corrosion. Your symptoms are that of a bad GEM. The GEm controls the transfer case along with the solenoids under the hood.

 

Hey having a bad gem would entail more than 4wd not working... Unsure but it sounds like a fuse or a relay not engaging I would check all 4wd relays and solenoids if you have vacuum in 2wd and it's not engaging on the dash it sounds electrical to me I agree with checking for corrosion and all relays and fuses as for a bad gem there would have to be more issues like the theft light flashing or something other than the 4wd not engaging to sell me on that one but crazy was a ford tech for a grip so Unsure on that one

 

wait so you have electronic 4wd switch? if so verify that the motor on the tranny case is working.