Long time lurker(don't post much), but i've been stumped by this issue that occured once I swapped in my rebuilt motor. I can outline all of the checks that i've performed, and what i'm thinking is the issue. I have a physical copy of the electrical diagrams, but mellens.net appears to be down at the moment. Stock ECU right now.

I rebuilt the motor with forged rods(cxracing), new bearings(mahle), new piston rings(mahle-clevite), a "new" '95 Head due to a headgasket failure(fear of it being warped) I removed the cas when removing the motor in fear of breaking the connector (needs to be retimed).

- I have spark, when key is in the on position an arc is formed from the spark plug wire. Spraying carb cleaner the engine will fire, good news! ( only checked Cylinders 1&4 for spark).

+ Car cranks over fine.

- Messed with main relay, i had the fuel pump priming after messing with the harness after cranking so i believe it is fine? I was unable to locate the relay for Fuel pump under the dash.

- Checked continuitey on the 15A engine fuse, under the dash. Checked 30A Fuel Injetion fuse in engine bay.

- Fuel pump has been verified to be working by jumping GND to FP in the diagnostics box.

- Ground to intake manifold near throttle body is connected, ground from engine/trans to body (near brake booster) is connected, Injector harness ground is connected. ( I plan on taking them all off cleaning each one.

- Current error codes I was able to pull (error code 4 CAS) & (26 carbon canister removed). I understand the the ecu uses the cas to sequence the injectors, if i am way out of timing it should still run, but run like crap?

- Possible that the fuel lines got reversed, but i put a ziptie to designate the feed and return lines to not mix them up.

Jiggling the main relay/ inserting it in a weird way will cause the fuel system to prime, but also triggers the cooling fans to turn on? (short is system?). Additionally, plugging/unplugging in the coil packs will also cause this to occure. Heck moving the harness ever so slightly can cause the fans to turn on. I went as far as disconnecting both temperature sensors on the back of the head and this issue still persisted. I removed the harness removed all wrap and then checked continuity to the designated pins, and nothing out of the ordinary. Even went as far as to see if any unwanted connections are made in the injector harness and was not able to find anything (checked contintuety between the two harnesses). I have the '95 injector harness i might just try to see if it works. Outside what i have checked what other possibilities are there?

I've been using this as a resource for the no-start. The intake and exhaust cams are timed correctly relative to the crank.

https://forum.miata.net/vb/showthread.php?t=279746

 

Fix: Main Relay (BAD) - Jumped currently ordered a new relay.
Fix: Cas was bad. I determined this by removing the CAS, then rotating the blade and listening to the injecters to tick, as well as the fuel pump to prime. Stuck in an old crusty CAS and viola fired right up.

Potential fix: Injector/coilpack harness was replaced, injector clips were not broken lol.