Hey so I finally have some time to fix some things on my truck (97 f150 XLT extcab, 4.6l 4x4 168,000miles), one being the 4WD. After days of reading and messing around under and in the truck I believe I have narrowed it down too 2 things. 1 the 4x4 dash selector switch, and 2 the electric transfercase motor.
Now I did some tests on the switch with my meter to see if I could get 3.9k, 1.1k, and 360 ohms. On the 2 center contacts I get 0 ohms when in 2hi, 1.1k ohms in 4hi, 360 ohms in 4lo. Obviously 0 ohms is bad as per the diagram I looked up which states it should be 3.9k ohms.
This data also backs up why it won't go back to 2hi. When I shift from 2hi to 4hi I hear a relay click-click about 4 times (once per second) in the dash, then the 4x4 light comes on and if im driving I'll hear a slight thud from the front differential. However, to go back to 2hi I have to put the selector switch to 2hi and turn the truck off and back on. Would this evidence suggest the 2hi position on the switch is broke??
I will be under the truck again tomorrow to see if I can spin the front drive shaft when in 4x4 and possibly use my meter to diagnose the transfercase shift motor.
Also I have already confirmed the solenoids on the firewall and actuator are working. I get vacuum on 1 line or the other at the actuator depending on 4x4 switch position and the actuator shaft slides in and out both manually and with the hoses hooked up. So at this point it appears my truck will engage the front differential with the actuator and says its in 4wd, but it is getting no power from the transfercase cause the shift motor.
If you got this far I salute you, and thanks for any help!
I doubt it's the switch.
The switch tells the GEM module you requests an action to 4x4h.
It in turn runs the transfer case motor to the first position engaging the front drive.
After the motor runs to the first position and the actuator operates, the signal back to the GEM module tells the GEM to turn on the dash lamp.
So the operstion is somewhat involved.
You need to first see if the case motor runs both ways.
If yes and there is no front drive to the differencial and the actuator works, then the trans may have an internal issue or the actuator splined sleeve for locking up the front axle may have an issue.
If the trans is stuck in 4x4, take the case motor down and manuelly rotate the shaft back to 2wd and motor coupling and replace the motor back on until a decision is made to repair.