Hi guys! I recently bought a 1997 f150 4x4 with shift on the fly. I bought the truck from an old man who parked it outside his house. I love the truck, but the 4x4 has been finiky.

I have done a ton of research and i have done a bunch of testing. The vacuum system is working correctly. I have tested the solenoids and the front axle actuator is working properly.

There is some kind of electrical issue. It might be the GEM (i really hope not), but it might be the shift on fly switch itself.

The 4x4 will engage, but when i turn the switch to 2h nothing seems to happen. Driving in reverse doesnt help. But sometimes it switch from 4h to 2h, just by turning the truck off and restarting it. If restarting doesnt work, then i have to pull the 5 fuse, let it sit, then put it back in. I read that this resets the GEM. (Number 5 fuse, middle row, 5th from the top).

Reseting the GEM usually does it, but not all the time. Sometimes it will still be in 4x4 again after reseting the gem. And then what is really weird, after driving it in 2h (after the gem reset) then turned it off and restarting it, it will go back into 4x4. All this happens with the switch set to 2h. So i have been having to reset the GEM, each time i restart it. (This was going on for a day or so.)

What do you guys think? Any easy testing i can do? Do you think it could be the switch on the dash, or more likely to be the gem? Im poor and i hope it isnt the gem.

Any experts? Any help would be greatly appreciated!! I dont want to have to pull a fuse each time to drive my truck.

Sorry for the

 

The Gem is on the back side of the dash fuse panel.
Check for a windshield leak that has dropped water onto the Gem and corroded the circuit board.
This causes conductive paths and uncontrolled operation.
The Gem is not resettable by any simple method. It has no temporary memory to clear.
Good luck.

 

In addition to checking for windshield leaks (semi-common on these trucks), pull the driver's side kick panel and examine the grounds. If you see ANY corrosion, clean the sheetmetal so it shines, replace the ring terminals and put in a NEW bolt, preferably stainless steel. My kick panel grounds were in poor to abysmal condition due to the lower ones being level with the carpet (trapped moisture makes rust). Don't be afraid to attack the sheetmetal with a Dremel & sanding drum. I gave each one a nice gob of dielectric grease after rehabbing to make sure they won't ever corrode and turn intermittant ever again