How do you tell engine size on 1992 ford ranger?

Look at the engines listed at

www.therangerstation.com

or

8 spark plug wires means 4cyl (two plugs per cyl)

else it is a v-6, in this case look at the intake/throttle body. if it sticks straight up and comes straight forward then it is a 4.0

if the throttle body is kinda swooped toward the drivers side and then comes forward it is a 3.0