One problem related to crankcase (pcv) has been reported for the 1998 Ford E-150. The most recently reported issues are listed below.
A thermactor check valve failed, causing exhaust gases to burn a hole in a/c hose, allowing freon and refrigerant oil to spray onto the hot exhaust manifold, causing a fire. This happened to a24-passenger bus carrying 10 elderly wheel chair bound residents of a nursing home.