EDIT: Just noticed your high mileage, which makes relay rack terminal resistance build-up even more likely, IMO.



Carl,

"I am thinking that there may be some sort of check valve in the fuel line to prevent the rail from depressurizing when the engine is turned off, the purpose of which would be to enable quick starts."

Yes, there is a check valve (replaceable) in the main pump outlet. It's purpose is to aid hot restarts by keeping pressure in the fuel rail (for a few minutes) to prevent vapor lock from hot engine "heat soak".

However, a good pump is said to bring up adequate pressure (on a cold start) within 1 or 2 engine revs. That makes your pump (or voltage to it) a suspect. You say the polarity is correct, but did you (can you?) actually measure the voltage at the correct terminal while the engine is being cranked?

Have you tried another FI relay or cleaned Fuse #1? These aren't known problems but I'm thinking of things that might reduce the voltage sent to the pump.

The relay rack socket for Fuel relay 86/2 is another suspect known to become resistive due to the load it carries, causing heat+resistance=more heat=more resistance...etc.

• I think that the 544 ECU is not known to cause this problem

• The ICU (a local abbreviation) is not integral to the FI ECU. I think your ICU is to the left of the driver's knee, with the ECU on the opposite side.

• I'd rather wait on the rich running symptoms for now.

--
Bruce Young, '93 940-NA (current), 240s (one V8), 140s, 122s, since '63.