Is the ECU correctly earthed, the return path for the earthing of all injectors and the Coils is the external earth connection that bolts to the ECU's heat sink

I know it's numpty but is it getting fuel when cranking? Are the plugs wet with fuel?

Yes the ecu is earthed, checked it is clean connection and continuity checked ecu body to earth ok. The injectors do operate, with throttle open whilst cranking you can see a squirt of fuel go in. They only operate once (or twice occasionally) like the ignition. Again pointing to CPS. However, 3 sensors tried, gap checked, phonic wheel looks good all teeth.

maybe a dodgy Sidestand switch or sidestand fuse in the fuse box ( yes on some models they run the earth for the sidestand interlock through the fuse box). Pretty sure the Neutral doesn't go to the ECU on that model

It's as if it's firing at the wrong time, like the timing gears are out of alignment. I suppose there is a remote chance the wood ruff key has failed. Doubt it but at the stage you are it maybe worth checking.

Hi, yes am going to re-visit the sidestand switch circuit. Not the switch itself as I know that is ok but the wiring to it, The switch and cct work ok to enable the start solenoid to operate but will check insulation resistance to earth as there may possibly be a fault causing the engine to cut off as this cct also goes to the ecu to kill the engine if sidestand put down when running.
I have contemplated the woodruff key ( had it happen on a car once) but thought I woulsd still get a spark whilst cranking, albeit at the wrong time. Stranger things have happened though so glad for your tips guys.

Checked all ecu power supplies at body 27, 17 and 4 pins, all good and comparable. Rechecked ecu earth at body 38 via sidestand switch, tried jury wiring it to be double sure. Checked eng earth, ecu earth again, battery earth, tried new fuses when reseating them, still the same.
Although I have measured resistance through the sensors from the ecu connectors I do not know the correct values but all seemed reasonable and as expected. Does anyone know if either the throttle position sensor, air temp sensor or water temp sensor would inhibit starting if faulty? You mentioned you had a problem with an air pressure sensor once dunlop o. Anyone know the sensors correct values?
Also will try pin pull-off check and then insulation check of the rest of the ecu wiring wire to wire and wire to ground.

pretty sure faulty water, air temp and air pressure sensors would just cause it to deliver the wrong mixture as these just adjust fuel trim values of the main map.
TPS and Crank sensor could possibly cause an issue as they determine where on the alpha-N map you are sitting, if TPS is faulty you could be sitting out side the map parameters, not sure what problem this would cause as there could be a default setting

Only ever had a faulty TPS once which was on the 620. Even so the bike would run just didn't rev very well.

You may have already checked this but are all the connectors in the ecu plugs correctly seated? None of them have got push back.

When the air pressure sensor failed the bike coughed and spluttered, misfired and then died. It would attempt to start but be an absolute pig until it back fired big style and set fire to the air filters.

I also am of the thinking that only TPS and timing (CPS) will inhibit starting as when TPS disconnected, no spark. When air temp/press or water temp disconnected, same as before, will not start but fires once or sometimes intermittantly whilst cranking.
Pin push back, pin pull-off check ok today.
Supply to sensors correct at 4.8 to 5V
Output from air press sensor 4.5V... don't know if that correct but seems reasonable.
TPS primary coil 520 ohms, output 60 ohms idle to 600 ohms full throttle with no dead spots.
Water temp sensor 5510 ohms
Air temp sensor 3280 ohms
All resistances measured from ecu. Volts measured at sensors.
Supplies to ecu ok.
All earths ok
Tried independant supply to coil sticks and injectors from pump/injector relay output to ecu body, same result
Tried jury wiring ecu body 38 earth lin (sidestand eng kill) same effect
Injectors resistance 14.8 ohms from ecu
Coil stick resistance 1.7 ohms from ecu
Tried starting with one stick and plug out and comination of plug/stick in one cylinder at a time, confirm same effect and fires both cylinders with any combo once or intermittantly.
Am starting to suspect ecu even though effect is same with both my "racing" ecu and the flashed one (to bypass imobilliser). My original ecu confirmed no ign switching at all.
Insulation checks not done yet, only done so far with multimeter not megger.