Fuel pressure spring

There is two valves in the pri filter base, one under the return line that goes straight up that takes a 1" wrench. That's the regulator that maintains the presure. The one you want to replace is the check valve that holds that presure after you shut the engine off. It is located right behind the return line on the side of the filter base. It also takes a 1" wrench. If he only replaced the one valve that's most likely his problem.