[Richard L]

I believe the way the fuel injection system works is not normal. Most system have a constant +12V on one side of the injector and switch the other side of the injector to ground.

By studying the frawing you sent, it appeared this system switches both. This is possibility the reason for the WI system have issue to read what is going on.

Please keep me updated. By the sound of it, you swap engine as simple as changing spark plugs!