I had owned a 1991 F150 4x4 for many years and it was a great truck. I recently traded it for a 2001 F250 SD 4x4 Crew Cab w/PSD because I had always wanted one. As I am now discovering, they are a whole different "animal". I love the 01 SD but I have been very dissappointed in the 4x4 performance in snow. But I'm not sure if it's the truck or if I'm being stupid! (no owners manual came with the truck)... So here's my question:
The truck has factory "manual" hubs (lock/auto) that work fine. When I bought it (in Sept, warm weather) the in-cab selector switch seemed to work fine to change to 4x4 high & Low Range.
Now in December (10-20 degrees) with our first big snow & ice, the truck does not seem to want to go into 4x4 using the in-cab switch! (hubs set to auto). The light comes on on the dash, but the front wheels don't pull. If I get out and turn the hubs to "Lock", the front wheels will pull just fine.

I know the transmission has to be in Neutral to shift to Low Range, but what about 4x4 high? Is there a problem with the vacuum system in cold weather? .... My old F150 had a manual shifter inside and you could FEEL the "CLUNK" when 4x4 was engaged. This newer SuperDuty is too smooth and "cushy", I can't "feel" what's happening under there! - Perhaps I just need to learn this newer truck, but if any of you guys can help me, I would be greatful!

 

Most likely its a vacuum problem. I would check first for cracked or broken lines. Also when you turn the key to the on position to let the glow plugs run you should be able to hear the pump run. If you can't then it might be bad. Basically just start tracking lines and the pump.

 

I had that happen on my 01 PSD dually. It fixed itself when it warmed up. I had a 91 like yours...I still wish we had the floor shifter instead of all this electronic crap as when you need it its not there!

 

I too feel your disgust with the ESOF system. Tomorrow I will be installing Warn hubs on my front axle. These are a direct bolt on replacement for the stock lock outs. But they are the traditional mechanically actuated lock/free hubs I like. The stock hubs use vacuum to engage them, so if there is a vacuum leak you will not get any front drive in the auto position. I am having unlocking problems with my hubs, that is why I am replacing them. There are many possible places for a vacuum leak to happen besides just vacuum lines. The hub seals, unit wheel bearing seals, axle housing vacuum fitting, etc. Fortunately the vacuum only works the hubs and heater controls. So with the Warn hubs I just plug the lines going to the front axle. I have also found out our ESOF t-case can not be converted to a manual shift t-case. You must swap out the entire t-case, and do the appropriate floor cutting for the shifter. That is the direction I am going in because I hate this crappy ESOF.