Is the car 5spd? Could be as simple as the computer doesnt think you have the clutch pushed in when your starting it. That would explain why once it starts it runs fine.
^ If it was a neutral safety switch (or clutch pedal switch), The engine would not crank.
^ If I’m not mistaken, SR’s only have a Cam Angle Sensor. The newer Nissans have 1 crank and 1 or 2 cam sensors depending on the number of cylinders though 
This could be true, the advice given was not SR specific…just a general no-start diagnostic lol. I’d get more specific if I had the vehicle and service literature in front of me
Update
- Checked fuel pressure just after fuel filter and got ~40psi at idle, and ~40psi when priming.
- Swapped another ecu in
- Have spark (checked when not starting)
Leaning towards CAS now. Fml.