The engine P1787 Code describes about the car engine problem. Here, the problem of the car engine can be a poor fuel pressure regulator what need to change or replace for solving the car engine. If you do not know how to solve this problem, you must engage an automobile engineer to check the problem and fix the car engine issue. I hope the problem of the car engine will be fixed sooner and you do not need to work hard or you have to pay more money for solving the car engine. Once the car engine is fixed, you must drive for a test.