Looking at your no “engine start” condition logically you have two clues.  Your immobilizer will not turn off and your OBD port is not functioning.  You have convinced yourself that the problem is with the immobilizer so why can’t you communicate with your ecu through the OBD port.  Both of these functions are to do with communication.  It could be that your ecu is not ready to perform both of these functions.  As you have discovered the immobilizer function is very difficult to diagnose,  its designed to keep thieves from steeling your car.  However the OBD port should be operational when ever its called on for diagnosis even when the immobilizer is active.
 
I assume the scan tool you are using is of the correct type for this ecu  so why does it not communicate.  I would concentrate your efforts in this direction.
 
One very common error I have come across with conversions is the way the 12 Volt supply is introduced to the vehicle.  Not many realise that with modern cars of today use two 12 volt supplies.  One is a permanent 12 volt supply which is active the whole time to cater for security and homework the ecu is doing in the background.  This 12 volt permanent power is important for the ecu to carry out many obscure tasks.   The second 12 volt supply is when the ignition is turned on to start the car and of course power up many other things.
 
I have seen many conversion that don’t have the required permanent 12 volt supply and this is only added (12 volt relay) when the ignition is turned on.  The ecu has not had a chance to do its homework and get ready for an ignition start and sometimes strange things occur which may prevent security issues and normal engine start ups. 
 
I am not sure how you have wired up your V6 conversions but I hope the above helps you.

resistor didnt give any communication 
 

Not saying this is your issue but might be worth eliminating. Check that you have power to the required circuits while cranking (not just ignition on) as some circuits lose power on cranking.

Also, is the behaviour the same as n aurion re not immobilised. Ie does it crank and not fire or not crank at all? This might help you narrow it down.

Cheers

Eric
we worked through the night and figured out the immobiliser. we also found some faulty connectors and fixed those.

The question that needs to be asked is, If what you found wrong as mentioned above is likely to give the same result as you have currently have now, on an engine that you would assume to start and run normally?  If the answer is yes then you need to try another matched ecu.
I know this was done earlier but this was before you found these new faults/errors.
 
During my usual work I always carry a spare ecu with VATs disabled for times when I suspect a possible faulty ecu.
 
Having no Can tells me the ecu is not running.

So was the pedal controlling the throttle before you found the errors with the wiring?

Congrats👏


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Well done man! What was the issue?

Helps when you put petrol in the tank. Joking lol