Brian,
Been a while since I layed hands on a Cedric. Working from memory so forgive me any errors.
ECU was either behind dash on floor centre (tunnel area or behind the NS kick panel (footwell area). Self diagnosis conducted by turning a screw (on ECU) all the way (CW/ACW can't remember) to the end which kicked in the flash code reader and gave a serious of flash codes.
If one LED is shown then a long flash = 10 and quick blinks = units. 5 long and 5 short flashes therefore = 55 and was the no fault found code. Cannot recall all the others. Please try ther Nissan dealer again for a manual as I was sure these were available all be the cost is around £50.
These types of faults are never easier on older cars as older mechanics with history of these vehicles are rare. Plus cars with donor parts (for elimination) don't regularly visit the workshop.
One thing I would sugest eliminating - the Air flow meter. Simply unplug it and then start the engine as this will allow the vehicle to run from pre-programed data (fail safe mode, allthough it will not rev above 2500 RPM I think).
Apart from that the fuel pressure regulator may be jaming the flow of fuel if the diaphragm is rupturted.
That's all I can add
Tony