XR25 cable or complete machine, or known good ECU, to diagnose engine problem

Hi, I have running issues on my long term project and need to diagnose if it is ECU or sensor related. Does anyone have a compatible XR25 cable to run on the PC based XR25 program that I can purchase? Or a known working ECU?
The issue is the car starts poorly eventually then runs for a few seconds on all four cylinders then cuts out again. Any throttle kills it. Immobilser is bypassed.
It has had an engine rebuild, the cam timing is spot on using correct marks, most of the engine sensors are new, the loom has been inspected, the fuel pump and pressure is to spec, all cylinders are sparking. New plugs, cap, rotor leads etc.. Picoscope test shows poor spark though so I suspect internal ECU fault but I would like to rule out any dodgy sensor readings using XR25 first. I suspect water has got into the ECU but it looks dry now. Are there any Renix ECU experts out there?
Any suggestions welcomed.
Thanks
Kent