SR20 Fresh Rebuild Won't Start

[LuckyX2]

So I just rebuilt the bottom end with new bearings, rods and pistons (they're 10.5:1 if that makes a difference) and now I can't get it to start. I didn't have time to stick around with it in PA since I had to get back to work in NY but my dad is currently working on it back home. So sorry if I'm short on info; I'm not in direct contact with the car.

Some info:
-Has a Haltech Platinum 1000 (useful for diagnostics)
-Upgraded to ID1000 injectors during the rebuild and changed the appropriate parameters in the ECU (Dead times, 1015cc, fuel pressure went from 4 to 3 bar)
-Has LS2 truck coils set to 5ms of dwell time and 12v source is wired directly to the alternator power to eliminate any issues powering the coils while we're trying to get it working (they weren't getting a full 12v before). It will go back to a switched source later.
-Cleaned BKR7E plugs (could probably use new ones but the old engine started fine with them)
-Cam timing/CAS has been double/triple checked and CAS was set at same position as before as marked with a sharpie.
-Everything was working before the rebuild! The engine took a few cranks to start and would backfire sometimes but it always managed to start.


The issue:
Won't start (as you already know). My dad seems to think that the spark is intermittent, firing sometimes and not other times as determined with a timing light. Also he claims that when the battery is fresh and cranking the engine quickly, he hears nothing close to the engine trying to start but when the battery dies down and cranking it slowly he can at least hear the engine pop/backfire and just generally make some kind of attempt at starting.

I found that last part particularly strange. Ideas?
Thanks

[ForeignMuscle]

Have you checked for power through the ignitor? I swapped my engine to a different chassis and somehow the ignitor went bad while out of the car. Meter your injectors as well to assure you have fuel. You can pull a spark plug out and set it on the engine plugged in the coil, unplug that injector and turn the engine over to check for spark. Very little spark from the plugs will crank the engine or make it very obvious that it is trying. I doubt it is spark, honestly. Tell us what you find after another trial.

[LuckyX2]

It doesn't have the ignitor anymore due to the LS2 coil conversion, it's just the signal wires going directly to the coils.

I think my dad is going to get new plugs today. I'll ask him to pull the plugs and check spark quality before and after. I believe he's already confirmed that the injectors are firing. If they weren't though, it wouldn't be backfiring occasionally like it does.