if you are trying to just remove the sap and don't care about the finish then try some harsh abrasive soap.If you are interested in saving the finish, hot water will remove most of it. Sap when hard is like sugar, hot water will melt it. Lay a towel on say the roof saturate the towel with hot water leave it there till it softens the sap, reapply the hot water if needed. I've cleaned some of the worst sap messes up this way. Elbow grease is the best answer and the best way to learn a lesson about car care.