primastar non start?

hi iv a 53 nissan primiastar runs fine when stated. the glow plug circuit is working ok. iv replaced cam and crank shaft sensor and appear to have fuel pressure and will start by bump start not jump start. iv also replaced starter motor and battery and gear box earth but to no avail.the fault acures hot or cold seems to want to start from cold but does not without the aid of easy start but when hot is showing no sign of life. ive tested the fuel injectors which pulse . As ive said it runs fine but just does not want to start. any ideas ?