You may want to download any diagnostic codes in the ECM. The following link tells how to pull the computer codes off pre 1996 GM vehicles:
http://www.geocities.com/dann8785/se...nginesoon.html
How you tested and got weak spark may be normal.
Notes on Electron ignition systems: These systems have one coil that is wired to two opposing cylinders (one on upstroke fuel laden intake cycle, one on upstroke exhaust cycle). They send spark to both cylinders at the same time, but only the fuel laden one actually sparks - this being electricity's path of least resistant. By testing for spark thru the wires (no fuel environment), spark may be equally split over the two cylinders appearing weak.