Jcamaraza

I have a 1996 Mack 688 with a 300Hp motor. Truck looses prime when turned off. Once started with ether runs like a dream with no issues. Had a mechanic come over and is leaning towards a fuel injection pump. However I’m no mechanic but if the fuel injection pump is working fine when the truck is running I’m thinking the problem should be somewhere before the pump. Any information from those who know better would be appreciated. Thank you!