94 Caravan - fuel pump won't run

The van has been sitting for a while, but started fine 2 weeks ago. A
few days ago it cranked fine, but the fuel pump didn't do the normal
2-second pressure up when the key was first turned on.

I can get the fuel pump to run if I jumper the fuel pump relay, so the
wiring to the pump and the pump itself seem to be OK. I tried swapping
the ASD relay with others (they all have the same PN, and all show the
same resistance between the coil terminals), but nothing. I tried
jumpering from B+ to the coil +, still nothing.

What else can I try? Is there a fuel pressure sensor that thinks the
pressure is up, so doesn't tell the pump to run? I don't think it's
the Hall effect, since it doesn't come into play until it starts
cranking.

Thanks
KC