Mk2 cupra ecu problem

[Mozzy]

Hi , I've been repairing a friends mk2 cupra after it had some fire damage which killed the old ECU and some of the loom, I got an auto electrician to come and repair the loom, and then tested the car with an ecu with matching part numbers, the car then started but immediately cut out because of the immobiliser kicking in, I then sent the ecu's to an ecu specialist who copied the immobiliser codes to the new one, now when I connect the replacement ecu, it no longer displays "safe" on the dash and can here the fuel pump, but it's now not firing at all and if you leave ignition on, after about 15 seconds the cooling fan kicks in, and my diagnostic equipment is showing " ecu no communication" anyone have any idea what's going on.... I know the loom is good, and the ecu came from a running car