Been away with work for a while so just got back to the Guzzi , i bench tested the injection relay and found it to be faulty so replaced with another new one and all ok with the voltage now, the relay was a brand new Bosch but not the first time i’ve fitted an electrical component out the box and it didn’t work. But the bike still won’t start.
Going back to my original question from this post “ Is there a way to test the injectors or ECU signal? “ When the ignition is turned on there is 12V on the injection relay circuit for a second, the fuel pump turns on for a second then stops because its voltage feed is dropped to 3.5V by the ECU. So to test the voltage for the injectors there is 3.5V at the plug with ignition on and 12V intermittently when cranking.
I took the injectors out and connected a 12V battery with a push button to test. Pushed the button for a second , nothing , pushed for two seconds, nothing , pushed for three seconds the solenoid clicks , again for three seconds it clicks then two seconds it clicks then one second it clicks then immediately , so on/off a few times and works fine. I filled the injector body with fuel put 3bar air pressure on it pushed the button and got a nice perfect spray pattern , did it a couple more times then repeated the same process with the other injector. Fitted the injectors , a couple of crank overs to prime then it fired up and went onto a nice steady idle, so works great now.
So the fault was the injector solenoids had been sat for too long and they just needed a bit more than a quick flash of 12V to kick them of their seats again.