baskervi

This is for a 2003 F150 5.4L 7700-series 4WD truck.

I have a 4WD vacuum actuator (I'm was just about to purchase a Doorman 600300 actuator), but I thought I'd test the vacuum first. I have vacuum on one line with 4WD enabled. When I select 2WD, the actuator stays in the 4WD position. I pulled off the two vacuum lines, and there is vacuum in the 4WD position on one line, but nothing in either vacuum line in the 2WD position.

There is a coupler a ways up the line, and it appeared to be separating, so I plugged that in better, but still no vacuum on 2WD. I found two solenoids on the firewall, and both solenoids have full voltage whether in 2WD or 4WD, and the voltage doesn't change in polarity when I go from 2WD to 4WD. There is a vacuum on both lower vacuum lines to both solenoids at all times. It baffles me, but somehow at one of the solenoids in the 4WD position, there is a vacuum on both the bottom and top vacuum lines. I'm not sure how the vacuum is triggered on the 4WD solenoid, but that seems to work. The other one (presumably the 2WD solenoid) has vacuum on the lower vacuum line only and none on the top one.

Can anyone give me suggestions as to what I might try? Thank you.

baskervi

I was able to fix the problem. I replace the 4WD disengage solenoid on the firewall, and it now shifts into 2WD in the front end.