STIR water and coffee crystals in medium saucepan until dissolved. Add evaporated milk; heat over medium heat to 175°F. Whisk egg yolks and sugar in medium bowl until well blended. Gradually whisk about one-third hot milk mixture into egg mixture. Return egg mixture to saucepan. Cook and stir over low heat until mixture reaches 160°F. Remove from heat. Whisk in 1/3 cup fudge topping and vanilla until blended.
FILL a large bowl about halfway full with ice cubes and very cold water. Set a 2-quart bowl inside the large bowl. Pour ice cream mixture into the 2-quart bowl. Stir until very cold, about 5 to 10 minutes.
FREEZE in ice cream maker according to manufacturer's instructions. Working quickly, spread ice cream mixture into crumb crust. Sprinkle evenly with pecans. Cover and freeze until firm, about 3 hours. Place remaining 1/3 cup fudge topping in heavy-duty resealable bag. Cut small corner from bottom of bag and drizzle topping over pie. Garnish with whipped topping.