Only starts with a scanner plugged in

What is your question?

I have a 2003 g35 sedan. Swapped the engine and now it cranks but doesnt start. Plugged in a scanner and knock sensor bank 1 came up. Changed the knock sensor still no start. But once i plugg in scanner it starts right up no problems and detects no codes but as soon as i unplug it it turns off and wont start without the scanner plugged in.