To give a little more background, I've used a JimStim on it's lowest setting (~45-50 rpm) to monitor the response of the MS-II - the MS-II sees crank pulse, cam pulse, 4 crank pulses, 2 cam, 4 more cranks, then another cam, and somewhere around there or the next crank pulse, it decides to fire.
This is totally illogical, especially on a bank fired motor. But even on a regular one, it's no big deal to run banked for a short time.
To steal some text from the MS-efi forums:
Playing the other side of the fence for a moment (I'll use the 99+ Miata as an example, I feel it's representative and I'm familiar with it) which works like so:
The crank has four teeth, two marks some distance before TDC, and two are just somewhere in between.
The cam had three teeth, a single at TDC cyl1 firing, and a doublet at TDC cyl 2 firing. Not exactly, but this is close enough.
To my simplistic view, two things will tell you where you are. Either
1) You see a signal on the cam sensor. You know you are near TDC on cyl 1 or 4
2) You see three pulses on the crank. You know you are a few degrees before TDC.
On a bank fired motor you can fire the ignition on coil pack A shortly after condition 2. You will have passed TDC, and even if you are a little retarded, the extra kick will get the motor going faster. For condition one, you likely can fire coil A by the same logic.
You could make the argument that you need to let that opportunity go by (though I don't think I would agree), but at most, two crank teeth later, you could fire the coil.
This should work for any bank fired motor. A missing tooth could be fired after only a few teeth to establish a time base and then a miss.
My only guess is that this is a noise rejection scheme, or to maintain compatibility for non-bank fire cars. Of course, nothing would keep you from firing pairs of coils until you achieve sync on a dedicated coil motor.
So, now that I've laid out the simple version, someone explain to me why it's a bad idea. The theory, while simplistic, seems workable to me.
....
Anyway, my real question is why not fire first, sync later? Is there a hole in my earlier logic? It would still be "cranking" and "unsynchronized", only it would fire the plugs.
I agree with this as written above - that you should define a state (which, for some engines you might not use!) where you know where TDC is, and/or you know what revolution you are on, and act appropriately. It'd be a "fast start" mode, where you don't need to be SURE you're firing at the right time, truely any spark after TDC can only help. So you bank fire the plugs and injectors as soon as you see the first pulse of any sort following a TDC pulse. If you wanted to push it you could do more guess work to figure other things out (more than half the crank pulses without a cam pulse means the second bank might be ready to fire), but all in all there's a lot of room for improvement.
And suggestions. Please do so!
