1992 5.8L mystery start then dies
 

Just an appeal for your wisdom with a 1992 5.8L that starts then dies within about 5 seconds. Replaced (so far) the fuel pump (was 20psi, now 45psi), fuel filter, fuel pressure regulator. Replaced the Distributor, Cap, Rotor, Wires and Plugs. The IAC valve, MAP and ICM sensors. The TPS sensor throws codes when WOT so it works and so, too, the ECM (probably). The only codes at KOEO are 55 (no or low volts (less than 7.5 volts) Key Power to ECM pin 5) and 56 (Vane Air Flow (VAF) or Mass Air Flow (MAF) sensor high - VAF MAF) although I have a MAP, not MAF, sensor in this year engine. The key ignition is broken so no key is needed to turn the ignition; but it has been like this for 6 months so it's an unlikely suspect. Spraying Starting Fluid into the throttle has no effect. I have a strong spark on all plugs. I can hear the new fuel pump engage when Acc is turned on.
I'm completely mystified and have no solutions.
Can you help?

It sounds like you have a lost or poor ground in the system. If you start with every ground connection you can find, make sure it is clean. Check the grounds for the engine components and the ECM.

If you haven't found the problem before I can return I will try to locate all the possible grounds for you to check, but it won't be until late this afternoon.

Did you check the mag pickup in the dist?