I own an older New Holland L555. I have also had the same problem with mine. These are the priming procedures for my machine, that has worked every time.
Loosen fuel filter and pump hand primer till fuel spills out and no more air bubbles. Hand pump only pressurizes to the fuel filter, if I remember correctly the injector pump takes over from there.
Tighten fuel filter and make sure their are no leaks.
Break each injector line loose, one at a time, and crank engine till all air is removed and fuel streams out. Each line takes only 10-15 serconds. This is easier to do with two people and fresh batteries.
Tighten injector lines and machine should fire right up.
Their is no automatic air bleed system on many older new hollands.
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