Well, the entire internet seems to be full of people with my same issue, but haven't had much luck getting solid answers.

Van runs fine. Never stalls. Occasionally after being parked, it'll crank but won't start. Power is being cut to the fuel pump. It doesn't prime when the key is turned on. Sometimes you can wait 30 minutes and it's fine, other times it won't start for days.

- Fuel pump was replaced. When it won't start, jumping 12v directly to the pump still activates it.
- a "Newrockies Pro Module" which is a Passlock/Security bypass was installed, so it's not a security/key/immobilizer issue.
- I have a new Fuel System Control Module (FSCM) on the way.
- Replaced all relays and fuses.

Wondering what else I should check.

It sounds like the Crankshaft Position Sensor and Oil Pressure Sensor can cause a power cutoff to the fuel pump?

Just hoping someone has some ideas!

 

Update: New Fuel System Control Module/FSCM installed (Dorman 601-022 which claims no dealer programming needed) and no change. Cranks, won't start.

 

Further update:

- If I wire 12v directly to the appropriate terminals on the fuel pump from a spare battery, it runs.

- Checking the fuel pump connector across the pink (ground) and larger gray wire (12v), there is 12v coming in from the FSCM, but when connected to the fuel pump, it doesn't activate it.

There are two additional wires on the fuel pump connector, a purple wire and gray/white wire, both smaller than the pink and gray wires.

Does anyone know what those wires are for?

 

wiring diagrams: http://www.revbase.com/BBBMotor/Wd

 

Thanks for the reply! The link doesn't seem to be working for me, are you sure it's correct?

 

It's correct. Seems to be down right now. Try this one:
https://www.gmupfitter.com/pages/body-builder-manuals