UPDATE:
Well, I pulled the ECU, and sure enough, it has the capacitor leakage problem. The electrolyte from the 47uF cap has done significant damage to the traces and through holes, and it just so happens that the injector driver transistors are right in the same area, with two of them having corrosion at their leads. I'll be working on the board and ordering new caps this week, and I'm keeping my fingers crossed that that's the problem and that the PCB isn't too badly damaged. Thanks again guys for the tip that led me in that direction. Also, thanks for the ECU pinout, Rick. It may still come in handy.

-Allan

p.s.- I'll post some pics of the damage later.