I'm in a right pickle with this now.

There is a strong spark.
There is plenty of fuel coming in
The distributor and map sensor has been replaced (and the ECU tests good too)
The injectors are all getting power
The main relay is clicking 3 times


All I've been able to discover is that cylinder 3 has low compression but surely this wouldn't prevent it starting?

The engine initially just died during normal driving.

I take it I'm lost then?

Im about 1 week from getting a replacement engine but don't want to resort to that.

See if reading sections A and B helps:

https://www.askmehelpdesk.com/cars-trucks/faq-how-troubleshoot-repair-maintain-honda-civics-46563.html

Low compression cylinder should be at least 80% of the others. My bet is you need to replace the head gasket:

https://www.askmehelpdesk.com/cars-trucks/faq-how-troubleshoot-repair-maintain-honda-civics-46563-2.html#post232786