1999 Windstar ECM Fuse

My 1999 Windstar keeps blowing its ECM fuse and it does not appear to be related to any particular activity. It has even been checked in 3 different shops and we tried using a 20 amp fuse, but it didn't improve matters. We have checked the grounds, wires, etc. several times, but to no avail. It will run fine for a day or even a few weeks and then suddenly blow it again. Does anyone know of any service bulletins on this issue or what this might be?