Link taken from -

http://www.hondacivicforum.co.uk/viewtopic.php?f=49&t=15389&p=117919&hilit=how+to:+change+immobiliser#p117919

Hello

This is a "how to" for OBD2a engines

Right so you have done and engine swap and you go to start the car and... oh no the immobilisers cut in!!!!

So your options..

-get a OBD1 ECU chip it
-go to honda and get them to pair your ecu and keys

OR

SWAP THE IMMOBILISER CHIPS!!!!

You need:
- Your origional OBD2a ECU
- ECU that runs your new OBD2a engine
- Solder Iron
- Philips Screw Driver
- Tools to take off ECU (10mm spanner)

Take the 2 immoblisers away from the car, get some clean to work on them.

Remove both the front and back plates from the ECU's, should be 4 screws on each side

Now you should have 2 ECU's that look like this:





right, now comes the hard part

You need to carefully take hold of this chip whilst soldering the pins. Pull gently on the chip to ease it away from the board. I soldered it from the top but ive heard its better to do it from underneath.

PATIENCE!!! Dont rip it out you will pull the pins off the chip. If this happens dont worry just solder them back on.



Remember which is the chip that is pair to your keys, that will need to be re soldered into the new ECU.

Hold the chip over where it needs to be soldered and melt the solder whilst pushing the chip gently back in. Once its in DO NOT WIGGLE IT!!!

Now simply place the covers back on the front and back

Refit new ECU.

Now your car should start.

Ive done this twice now and both times it has worked.

I cant garentee it will work.

Tony (TonyCoupe97) from Honda Civic Forum.