David remarked of higher solder joint failure rates for hot components.
The injector drivers run relatively hot.
Could we assume the injector drivers are not getting enough current to open
the injector solenoids due to faulty solder joints limiting current flow?
Noid light only shows the signal, not the strength, as Mark pointed out.

I would be very interested to see if reflowing the solder on those
transistors would solve the problem.
If so, don't bother with a spare ECU, just carry a butane powered soldering
iron:)