fuel surging.

Hi everyone. still having problem with my td5 gs ,its had new pump filter and 3 injectors and it still appears to have a intermittent missfire.took it to a different engineer who put a pressure gauge in line and said the fuel is surging. does anyone out there know how to fix this, its not always present engineer comes says it ok the a few days later it starts playing up again.Cannot see any fuel leaks etc.