somewhere might be leaking in air or fuel blocked.
1. ensure fuel feed from tank to Primary filter is ok.
2. all hoses and connections (elbows at Primary filter, Banjo connector at Sec.Filter), bleeder nuts, filter locking rings/nuts are not leaking.
3. use manual pump at AC Pump (1st low pressure pump) to prime fuel thru' Primary filter and bleed off at Sec.Filter.
If your engine had start normal before this problem arises, chances are its due to starvation caused by air leaking in from somewhere along the fuel supply. This lesson cost me $1200 and I'm sharing it with you. Good luck!