1. What is the compression? You will chase your tail if you do not do something as simple as this.
2. Do I have a fuel or electrical problem?
3. For spark, I will remove said spark plug wire(s), install a good known plug that will jump a gap, ground that plug to the engine, hit the starter, note if I have spark? I have now eliminated spark and compression.
4. My fuel is next. I only have 3 variables, so it is one or the other, not both or all 3 in a way of process of elimination.
With fuel injection, there are sensors needing 0 to 5 volts. If 12 volts drop too low, say down to the low 11 volts, without that charging system kicking in to boost the volts back up, it will be difficult for the sensors to give their designated output signal in the 10ths of volts. Lets say a sensor needs 4.30 volts to send a signal the computer recognizes. If the main volts [12v] are low, it will be hard for the computer to send a spark in other words.