NO Start issue after Engine swap, HELP!

[Qmulus]

You are on the right path with the wiring. Get the body harness to engine harness wiring correct, then get the OBD communication working. You will then need to get the DME matched to the immobilizer before you can even attempt to start the car. For this, you will either need to take it to a dealer, or find someone with a PST-2 or PIWIS II, etc., and get the programming codes from your car from the dealer. Then the DME and immobilizer can be properly matched. I would NOT recommend getting the immobilizer, DME and key from another car even though it would work, as this can/will lead to other problems down the road as your car would now be electronically whatever car you got the parts (by VIN) as far is Porsche is concerned. That means the programming codes, etc., for your car would no longer be valid. If you would need a key or DME programmed down the road, you would have to have the VIN from the car you got the DME and immobilizer from to get the programming codes to allow the process to work. If you don't have that, it can get complicated and expensive.

Sooo, what did you do about the fuel system? The '03 uses a single line, non-returning fuel system with the regulator on the pump, whereas the '02 uses a returning system with the regulator on the fuel rail. On the one car that I know that was converted from ME 7.2 to 7.8, the fuel system also had to be converted to get to operate properly. There may also be some communication issues with the ABS system and cluster as the ME 7.8 uses more CAN integration than the ME 7.2 cars did. That may not be evident until you get it running. I believe that the '03 also uses different oxygen sensors than the early cars. Did you also get these?