Do you have to drop the gas tank on a 1986 Cadillac Coupe Deville replace fuel pump?

No, you generally do not have to drop the gas tank on a 1986 Cadillac Coupe DeVille to replace the fuel pump. Access is typically from inside the trunk. There's a cover or access panel that allows you to reach the fuel pump assembly without removing the tank. However, some extra work might be involved in disconnecting fuel lines, electrical connectors, and possibly removing the fuel pump sending unit.