Was the 1991 cargo van made with a Vortec engine?
Did the 91 cargo van come with a Vortec engine? on 1991 Chevrolet Astro
This site can help you answer that question and more about your Astro Van: http://www.goodwrench.com/Downloads/index.jsp
look at the engine digit in your VIN number. (off hand cannot remember if it is the 8th digit or the 10th, one will be the engine code, the other the year.) if you have a "W" code, you have the Vortec. The other code for that year (non-Vortec) in a 4.3L IIRC is a "Z"