Answer to: losing prime on a volvo d12I run a 2010 VNL780 D 13 and keep loosing prime anytime the engine was shut down, replaced fuel filter housing because the prime pump was shot. and that still did not solve the issue. Pulled the injectors and all of them only had the top O ring in place. I replaced the injector cups and installed new O rings top & bottom on the injectors. Now the engine starts in a couple cranks. Problem Solved. about 610 K miles on the truck.