Injectors will not fire MK1b

[plank-08]

Hi everyone please help. I have a E reg MK1 MR2 and unfortunately it has had a electrical fire and burnt most of engine bay wiring. I have installed a new loom from another MR2 but am having issues. The car will start and fire up for approx 2 seconds and then cut out. I believe that the cold start injector is giving an initial squirt of fuel and the that is what makes car run. I am getting good spark and also fuel in the rail. I have proven that I have 12 v on the injectors right back to my ECU with ignition on. From what I have read the ECU is meant to pulse the earth connection to the injectors to dose the fuel. I have an oscilloscope and I have looked for pulses from ECU and have none. If I physically pulse the earth onto the injectors myself I can make the car run. I have replaced the ECU and still have same issue. Does anyone know what may be causing the issue? I assume the ECU requires an input from the RPM sensor in the distributor to work. I have also put oscilloscope on the connection from RPM sensor and can see a waveform reaching the ECU. Does anyone exactly what signal is meant to be produced? I have also run through the ECU diagnostic check and system says no faults?

Any appreciated,

Thanks

James