[fredjacksonsan]

It may have locking hubs in front, start there. Then check to see if there is a vacuum hose setup to the front axle; if so, make sure the hoses are in good shape. You said it won't go into 4lo; will it go into 4hi? If it goes to hi but not lo, you could have a transfer case problem. If you're considering buying it, why not take it to a reputable mechanic; they may be able to diagnose the problem and give you an estimate - a good tool for negotiating the price of the vehicle.