As in sleuthing if this was mine I might tap into the power leads to the pump and run them up into the cab so I could monitor the voltage to the pump. This is entry level electrical work so most technicians can do this. I take it you want to avoid just replacing the pump and hoping.
Another thing that I think is worth doing is replacing the fuel filter. I've lost count over the years where it just fixes odd problems like that. Here that's a few bucks and usually easy to change out. Why do I do this? An old mechanic saying "What's the cheapest thing it could possibly be?"
I have a 2000 ford escort 1.8i zetec...car runs well... once in a while, the fuel pump didn't kick in, but moments later it did... now it happens almost daily at random moment's... never stalls while driving but sometimes when im parked and go back to start it, fuel pump refuses to come on... safety system works fine, fuel pump relay kicks in, but cant get the pump to kick in all the time... help???