Hard to start any time of the day for 1994 Nissan Quest XE.

I was told the fuel pump is electric, so after inserting the ignition key I have to wait for awhile before starting and it crank but don't start then I have to pump the gas 4 or 5 times then sometime it will start. When It starts everything is running fine very smooth like brand new. Spark plug, spark plug wire are less than a year old, rotor are only few months old. One fuel injector was change due to malfunction, add fuel injector cleaner every full tank (it start easy when tank is full) and it fuel is less than half tank, the problem of hard starting begins. Did researched and it points to the fuel pressure regulator, fuel pump but not sure which one is to change. Otherwise the van is running like a champ. Please help me identify why it is hard to start.