First we have to establish whether your ECUs have any stock ROM chip. A ROM chip is an external memory whereby your ECU store both the program code and data. Some ECU use Microcontroller which has internal memory like Oki 83C154 in PM6,7 Honda ECU or Oki 66507 in a OBD-II P2T Honda ECU.  These MCU carry internal memory which are programmed into them using special programming devices.

Let us concentrate on those ECU that have stock ROM chips. First open up your ECU, look for a 28 pin chip that label 27128, 27256, 27512, 38128, 38256 etc. We will use Honda Civic 89-91 JDM EF9 B16A1 ECU PW0 for example. You look for the stock ROM on the lower left corner away from the connector plugs. It has marking printed on the chip : Oki 38256-15 and large number 71 which identified the stock chip program.

Now open back panel of your ECU and reveal the solder side of the ECU circuit. Desolder the stock ROM chip and solder on a 28 round pin IC socket. Now you can plug in your stock ROM chip or any racing EPROM chip that specific for this ECU.