According to Norman Deno in Seed Germination Theory and Practice (2nd Edition), the seeds of passion fruit (Passiflora edulis) germinate best if they are provided a moist, warm (70ºF, 21ºC) period for three months, followed by a cold, moist (40ºF, 4ºC) period for three months, followed finally by a moist, warm (70ºF, 21ºC) period (81% germination in the fifth week following the last temperature change).
In his First Supplement to Seed Germination Theory and Practice, Deno added the following information:
P. edulis had been found to germinate in a 70-40-70 pattern (2nd Ed.). Thelma Norman of Mena, Arizona, now reports some interesting results. Commercial seeds of P. edulis, P. antiquiensis, P. malformis, P. mollissima, and P. vitafolia were inadvertently exposed to temperatures of 125ºF for several days shortly after sowing. All germinated in 6-10 days. Presumably the chemical system blocking germination can be destroyed not only by 70-40 treatments, but also by high temperatures in the 125ºF region. P. cinnabarina and P. coccinea failed to germinate in the above treatment.
I, personally, suspect that, for passion fruit and some other fussy germinators, fresh seed may germinate more easily.