'87 5KTQ ECU-related problem again :-(

[MHLIGGINS@aol.com]

    I think last night’s “success” was a coincidence. The car decided to quit 
again today. And this time it seems more permanent. 
    Last night it would occasionally show the 2312 (temp sensor) error code. 
But when it was being the most stubborn it was showing 2.1 bar when I turned 
on the ignition and the fuel pump would start up immediately after turning on 
the switch. That's what it's doing today. I really think I've got a short 
circuit somewhere, or a ground fault of some sort.
    I tried removing/replacing the harness on the ECU like I did this 
morning. No go. I changed ECUs. No go. I changed the fuel pump relay. No go. 
Removed and replaced the ECU to manifold ground wire. No go.
    Does anyone know what could possibly short out that would cause the fuel 
pump to run and the ECU to think the turbo is in an overboost situation? FWIW 
I have a vacuum/boost dial indicator on the car now and it reads fine, so 
between that and the fact that both ECUs do the same thing I'm assuming that 
the pressure sensor is not the core problem.

    As always, thanks.
    --ml