The F/P to gnd short on the diagnostics connector, bypassed the circuit opening relay and grounds the coil for the fuel pump relay (giving the fuel pump power), but this will only happen with the ignition key in the 'on' position (reds). Sorry if i confused you Stefan.
I concur with maybe the fuel pump dying. Or blocked and cutting out.
I had a rodeo ute (Mr Q knows it) which the fuel pump cut out on me in my garage of all places.
I decided to drop the tank and pull the pump out so i could get another, it turned out that the pump had been replaced before, it was just connected with screw connectors
and one of these vibrated loose and come undone!
I soldered and heatshrinked the wiring back together and it ran sweetly for another 30000 Km's until i sold it last year.
I suggest maybe getting another fuel pump relay in case it is flaking out on you and not holding on. The reason i said that is beacuse you still had spark and I would have thought if the circuit opening relay malfunctioned it would disable the coils too.
If you need a hand replacing the fuel pump i can help, but i will be in Melbourne for the next 2 weeks.
Cheers
Nuno