* The owner's manual: This is the most reliable source.
* The fuel filler door: The sticker on the fuel filler door sometimes lists the capacity.
* A Ford parts website: Inputting the VIN (Vehicle Identification Number) might provide the specifications.
Without knowing the specific trim level and engine of the 1996 Ford Econoline van, it's impossible to give a precise answer. However, common capacities for that era ranged from 17 to 30 gallons.