Before replacing the fuel rail, however, you should verify that the fuel pressure regulator is actually the problem. Low fuel pressure can have several causes. Symptoms like hard starting, poor performance, or stalling could indicate a problem, but could also be caused by other issues such as a clogged fuel filter, bad fuel pump, or faulty mass airflow sensor.
To diagnose: You'll need a fuel pressure gauge to measure the pressure. A qualified mechanic can do this easily, or you can rent or borrow a gauge and consult a repair manual for your specific vehicle to find the testing procedure and correct specifications for fuel pressure.
In short: Don't just assume it's the regulator. Diagnose the problem properly before buying and replacing parts.
