So the starter engages twice and then won't engage again with the replacement ECU/SKREEM and key?

And with the original parts in the car you get no starter engagement at all?

THat's not making logical sense. But since you dont know for sure the history of the car OR replacement parts, I'd start with a voltmeter and the service manual wiring diagrams and see what you have and don't have (voltage wise) on the outputs of the RCM as well as ECU outputs to the RCM and pulse modules. The fuel pump enable comes from the ECU but you won't get that unless the RCM first provides "Engine control relay" output to the ECU. On one hand, it sounds like the RCM is bad, but it cant be since you can make the ECU light up and engage the starter with the replacement SKREEM and ECU.

If you are not experienced with electrical troubleshooting, you will be soon. GO SLOW at this and take your time. Keep notes of what you find with the replacement modules in the car versus the original parts.

Of course, the EASY way out would be to mail the SKREEM, ECU and ignition cylinder to the guys at The MSS and let them make a new compatible key (and even do the SKREEM mod). This business of buying donor car SKREEM/ECU/KEY can work, but it can also be a nightmare if the parts you buy are not actually working. And how do you KNOW they work?

If it was my project, I would have just yanked the original SKREEM, ECU and Ignition switch and sent them to the MSS. We all know that they would send back working parts the first time.