immobilised injector pulse problem

Probably long wires etc effecting the injector waveshape. Better to interrupt the injector +12V using an inverting relay if necessary.

^^this ^^^ If the relay contacts are even slightly resistive, it will affect the pulse duration and firing characteristics. Best to interrupt the voltage supply, not the controlled side of the injector. Even a 4 cyl engine will run on 2 cyls. And a 6 will definitely run on 4. You need to disable all of them. I'm not familiar with Honda EFI, but most contemporary port injected engines are sequential fire, ie the PCM controls each injector individually. BUT the other side of the injector is almost always +12V. Check wire colors at the injectors. If you find each injector has one wire of a color common to all the others, that's the +12V side. Go far enough up the harness towards the PCM, and you should be able to find the splice where they all come together. Make your interrupt there.