As Marty said, if no air prior to the DP, you should first look at the pre-filter o-ring (check the bolt and washer/hold down and make certain its tight) and also the o-ring on the fuel line that enters the pre-filter. Both can be difficult to get sealed again. A dab of silicone grease can be helpful if they refuse to seal as can crimping the washer to create more downward pressure on the pre-filter.

All the lil white horseshoe clips on the ends of the fuel lines should be loose and floppy when properly installed. They are pushed closed (eg: make a ringer) for removal.

__________________
Terry Allison
N. Calif. & Boca Chica, Panama

09' E320 Bluetec 77k (USA)
09' Hyundai Santa Fe Diesel 48k (S.A.)