Start sequence + low voltage
 

Question semi-dragged over from my initial meet and greet thread but perhaps more appropriate for an MS3 tuner discussion. Without completely rehashing the saga that has been my low voltage start sequence, here is the question.

At what RPM does the engine have to be spinning at, for how long, in order to successfully fire?

So, I'm chasing some wiring demons around to determine the cause of my ~1.4v drop across my battery to the starter but my concern here is that the engine isn't catching and ignition events are not assisting with the start sequence to create a sustainable idle. If the engine did successfully have an ignition event, even with a low cranking voltage it could in theory assist the starter and reduce the torque required and amp draw. However, if battery voltage drops too low, then it seems obvious based on the dwell tables for ls2 coils that the MS3 is making potentially massive corrections to dwell (unless it sits at the static cranking dwell?) per the startup. Also, for skipped pulses, I'm assuming that since this reads nearly instantaneously to synchronize, it should not be delaying more than 0.5 to 1 sec before initiating fuel pulses so really engine speed could be as low as 100-200 rpm assuming enough compression existed for ignition then as those events continued in time to speed up and create a stable idle near ~700rpm even if the starter is nowhere close to that speed. I'm still running fixed advanced at 10* of timing until I can sort this out.

The rest of the story is that I'm still chasing down the wiring assuming that my consistent 115rpm with an NB starter is "too low" to get a full fuel/ignition sequence and for that to accelerate to idle. My concern is that even if I do find the problem, I'm not sure what a stable cranking RPM is for an '05 engine with no ignition events occurring and per above, if an ignition event DID occur, if I needed to hit that target in order to successfully get the engine to light.

Much respect,
-Marvin

Just looked at a log from one of the miata's I'm e-tuning: 138-290 for about 1.5 seconds