my freinds 89 buick century station wagon and my uncles early 90s olds cutlass both have this problem....

one day they just ka-put, stopped running. we checked it out and it turns over, its gettin gas, but no spark. went and bought new spark plug wires, and spark plugs and its still not gettin ne spark. tested all the connections and wires and they showed up ok.... anyone kno what the problem is???
help is greatly apriciated. thanks