Hello dear Mazda enthusiast.

Me and my buddy is working on swapping a 2.0L(LF) engine for a 2.3L(L3) engine, we've swapped all electrical components that make sense to swap (Engine wiring, ECU, BCM, immobilizer / key recognizer, light unit and speedometer) everything seems right and almost everything is working, however when we try to start the engine the immobilizer lamp continues to blink, the starter relay doesn't click and the starter doesn't turn, neither does the fuel pump start. We had a tester (delphi) on it and it was unable to communicate with the ECU, furthermore when we entered modules such as ABS or BCM they both reported a error between Canbus and the ECU (U0100, U1900) we've tried several things and checked the wiring to make sure there wasn't any loose connections but without luck.

Car: Mazda 6.
Year: 2005.
Type: Stationcar.
Engine: 2.0 L Gas.
Engine code: LF
Transmission: Manual.

Donor car: Mazda 6.
Year: 2006
Type: Sedan
Engine: 2.3 L Gas
Engine code: L3
Transmission: Manual


TLDR:

• Attempts to swap a 2.0 L engine to a 2.3 L.
• All Electrical components swapped
• Light, power window, central lock is working just fine.
• When turning the key nothing happens.
• Delphi tester unable to communicate with ECU
• ERROR codes:

- U0100 - Error between Canbus and ECU
- U1900
- Wires are checked


Note:
Before starting the engine swap both cars have been confirmed running.
The 2.3 L engine has been disassembled and got its crankshaft replaced.

Any ideas would be welcome and appreciated since nothing makes sense to us anymore.
Thanks in advance.