Hi everyone, this is actually my first post on here but much needed by me. To start off her are the details-
truck-98 ford f150 extcab 4.6
4x4 type-ESOF(switch on dash)
problem-4x4 does not engage.

ok, so what happens is that there is no response of me turning the **** to 4hi or 4lo. there is no relay clicking and there is no 4x4 light that comes on. I have replaced the 3 relays under the passenger top dash panel next to the firewall which i was told could be the problem with no success and i know the 4x4 lights work as they come on at start up. Also i have had it on a scanner and it verifys the switch works going to 4hi and 4lo but it did have i believe a p1820 code which was for the 4x4 relay/module??and that is why i replaced those relays today, pulled the negative, reset the ecu, and now the code is gone but still no 4x4.....so this is where i am at now and i am leaning toward the gem module which i was hoping was not the culprit but want to get opinions from everyone and any for sure testing procedures to do as i am open to anything but dont want to be throwing money at a part that i dont need. PLEASE HELP thank you in advance

 

how are the fluids in the transfer case? its like a built in safety in a lot of vehicles i had an old dodge and any time the fluids where low it wouldn't engage in to 4x4... i don't know if fords are the same way but its worth a shot, good luck

 

i believe i have read about vacuum lines being a culprit for 4x4 problems. I don't really know much about it on here but im sure somebody does.

 

Right!

Yea, they become frail/dry out and break between the battery box and firewall. The Pink & Blue 1/8 lines, that run from solenoids (2wd/4wd) at the firewall to the actuator on the front axle.

Keep in mind, if your lines look good, then chances are, your actuator is hanging. You need a cheap Vacuum tool you can get from just about any 3rd party parts supply to preform this. WD40 the actuator rod on the axle. Disconnect the blue line at the actuator/ connect Vac tool/ supply vac (about 12 hgs), watch pin or rod for movement/reconnect Blue, disconnect Pink/ do the same.

Once the pin or rod moves, it's in working order, just lube it up a bit.

With the vac tool, you can also test the lines. Nothing special has to be done to preform. Leave the key off. However, you really need to remove the battery to check the supply lines thoroughly.

If you happen to get mixed up with what line goes where at the actuator, DO NOT follow Fords diagram from Service/Workshop manual. They have it back wards. It's best to mark these lines down on paper for yourself. This may only be with certain years.

Good Luck.

BTW- Problems elsewhere within the system could exist. These are two common ones.

 

jbrew- i have indeed read that the vaccuum lines can be a problem but was thinking it was more a power/input issue for the truck to think to go into 4wd because nothing at all happens when i turn the 4wd switch(no 4x4 light, no relay clicks, just dead silence). now i dont know if it needs the source of vacuum to do that but i would think that would happen after the truck at least trys to go into 4wd using its good ol brainbox. I just want to here somethin other than crickets chirping when i turn that 4wd switch lol

 

Ok, not trying to make you sound dumb.. But have you checked and made sure the switch is plugged in?

 

lol yes its plugged in and it is recognized by the snapon scanner that i have hooked up to it

 

have you checked the fuses. there's 1 under dash and one under the hood!!!