I have myself a nice 2003 F-150 Supercrew FX4 with the 5.4, auto, and that wonderful SOTF 4WD system. I love the truck, but I have a question about the operation of the 4WD system. I was trying to leave the oparking lot at work today and it was fairly slick with packed down snow from the day before. I parked the truck in the morning with it in 2WD. When i tried to leave, i had backed out onto a slight decline and couldnt get the truck moving in 2WD, just got some fancy rooster tails of snow. I tried goingt o 4WD HI, got nowhere, rooster tails. I tried going to 4WD LO, same thing. I can hear the front end "locking in" and I know the T-case motor is engaging. So here's my question :

Does the shift-on-the-fly system having to be moving forward in order for it to engage the front drivetrain and move the front wheels in 4WD? Should i be getting 4WD operation right at the point when I engage it with the dash switch? I had a 99 Ranger Off-Road with the same type system before my 150 and never noticed anything like this when I needed 4WD. It seems that even when I switch to 4WD HI while driving in the slippery stuff that it takes 50-100 ft or so until I feel the front tires start to "bite". I know the system is engaging but it just doesnt seemt o be engaging quickly enough or as quick as I think it should.

Let me know what you guys think. I've had the truck in for service once since I bought it about 3 months ago for the transfer case motor not working at all. Ford replaced the motor under warranty but I didnt really use the system regularly until a week or so ago when we started getting tons of snow.....

 

These trucks lock the front diff in by engine vacuum. Because of this, it does take a small amout of time. If it is not engaging and the 4x4 light is coming on, I would look for a vacuum leak in the diffs vacuum lines.