How do you change the plugs in a 1991 Chevy Astro van?

First you need to determine the size of your engine. If it is a 4.3L V-6 you need to open the hood AND remove the inside engine cover (or "doghouse") as it is referred to as. This will allow you to access all of the spark plugs through one or the other openings. All plugs with the exception of the two rearmost plugs on the drivers side of the engine can easily be accessed this way. The two rear plugs on the drivers side must be accessed from under the vehicle (unless you're a contortionist)! It would also be a great help to have someone inside the vehicle for these two plugs to help to guide your plug wrench onto those plugs as well as to guide your plugwrench to them when re-installing them.I have seen more than a few astro 4.3L V-6 engines where these two plugs were purposely overlooked due to the difficulty in reaching them. Total time; open hood-1 minute,removing "doghouse"-10-15 minutes,removing plugs AND replacing them-25 minutes,re-installing "doghouse"-10 minutes,closing hood-1 minute, washing up and having a much-needed beer-1-2 hours. These are approximate times for a novice. For a total beginner at least double these times! Good Luck!