From what i understand, the engine will start and stay running when starting fluid is used, wright? But will not start on it own, wright?
Seems like you have changed everything on the system except the IPR (injection pressure regulator) which will cause no start or hard starting.It is located on the high pressure pump screwed on the side. Need to change out.
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Do you have a check engine light that comes on?
Have you had a computer diagnosis done on the engine?If yes, what are the codes?