basics when u turn on the ign switch kill switch on u always have a check engine light on. that just tells u the light circuit is working. if u start it up and the light is still on that means u have a code.
you r making things to hard for yourself
first for now forget about the codes and the readers.
u need to go back to the basics.
in post #32 u said u had 6 volts at the fuel pump relay if this is correct and if u have 12+ at the fuses then u have a connection problem. fuel pump is not going to work on 6 volts.
the ecu is not your problem. if u r not getting 12 volts to the ecu then it is not going to work.
u need to have the volt meter on the bat neg and the fuses when u turn ign on if 12 v then check at fuel pump relay then engine management relay.
when u figure out what is happening to the voltage then u will have your problem solved.