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.

Hey Kojab, 

Gouky gave me some pointers regarding the OBD plug, he said that CANL and CANH need to ahve 56-60 ohms resistance between them approximately. 

This could be why it isnt comminicating.

I have inspected power wires coming from the ecu and they all go to where they should in regards to 12v battery power and 12v ignition
 
I will add in a resistor and see if I can get communication

resistor didnt give any communication 
 

Hey Eric,

You said that everything you've checked seems OK but it still doesn't work, therefore you have either checked something incorrectly, or you haven't checked something that's really important.

I'm going to list all of the things that I would check if I was there, no matter how trivial they may seem:

- Make sure that the GND pin of the Transponder Key ECU has continuity to ground.

- Make sure that there is constant 12V on the +B pin of the Transponder Key ECU even with the ignition off.

- Make sure that the IG pin of the Transponder Key ECU gets 12V when the ignition is on.

- With the ignition on, put the negative probe of the multimeter on the AGND pin on the Transponder Key Amplifier and the positive probe on the VC5 pin on Transponder Key Amplifier, then make sure you see a voltage (I don't know what it should be, but I'm guessing either 3V, 5V or 12V).

- With the CTY pin (door courtesy switch) on the Transponder Key ECU, I don't know if the switch would normally be open or closed when the door is closed (in an actual Aurion), therefore I'm not sure whether you need to have that pin permanently connected to nothing or permanently connected to ground, but it may need to be correct for everything to work.

- On the Data Link Connector, I assume that the BAT pin should have constant 12V even with the ignition off, so I would check that.

- Check the CG and SG ground pins on the Data Link Connector.

Most of the other pins/wires are interconnected between the various ECUs and modules, so they should be OK if everything is plugged in.
 
You didn't post any wiring diagram pages for the engine ECU, but maybe you should post those too.

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

ok i flew Troy up (he built the loom)
we worked through the night and figured out the immobiliser. we also found some faulty connectors and fixed those.
 
the car turns over but no injectors, spark or power going to the throttle body or pedal. still no can
 
its like the ecu isnt getting a signal to say "hey you can turn on"
 
we checked power circuits and all seem ok. any ideas?

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.

Eric, your a trooper mate! I'd be looking for matches by now :@

Keep at it you've clearly got heaps of people and support behind you :-)

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

Its alive.