I recently visited a Ford dealer to get some info of what could be wrong with my 4x4 system. I have a 1999 Ford Ranger with a 3.0 V-6. When i engage the auto 4x4; the transfer case enagaes, front axle spins and both front axles spin while on a lift. All i can think of is the vacuum pump or a broken or clogged vacuum line. I checked the hose going to the hubs and there was nothing. If anyone knows where the main vacuum source is please let me know. It's time to go wheelin'.