I can explain how to test components , sensors etc, The 2 ECU do talk to each other, but the system is very much mechanical....if lead free petrol is left in system over many years of being off road, then the Fuel metering unit suffers bad as does the 4 injectors, the old petrol turns a Purple/Red gunge, and the Fuel tanks rust on the inside sending fine debre which does make its way through the filter, That's with a good fuel pump and a working 5th injector working, and 4 good sparks on cylinders, these car will start right up...but once petrol used up 3/4 seconds engine stops....that's when you know the injection system from metering unit not working...as said gunge up...I don't know hear history of car ?......normal working is 5th injector starts engine instantly...the pressure actuator would have received a signal from the Black ECU to increase the pressure in the system [ much like the old school "choke" ] so engine runs fine...the idle has been stepped up via the "Fast idle valve"...as the engine warms up the pressure actuator and the fast idle valve return to preset condition...via the "Bi-metal principle" so then perfect idle 850/900 and lower pressure to 4 injectors, the Thermo timer is also "Bi-metal principle"..ie shuts down completely the 5th injector, so warm / hot starts don't need it, of course if it ever came in would flood the hot engine, ive all readings on any sensor....feel myself be good to hear engine run..as said...petrol in the manifold..4 sparks..must fire...the Black ECU has no bearing on the separate wired Pump/relay or 5th injector / Thermo timer..there are some fuses in system..circuit 50 is not. Peter