MS V3 PWM does not let you run low impedance injectors!!!!
 

It's taken me about two months, but I've finally figured out my spark troubles. I noticed that the problems were a lot worse when I turned on acceleration enrichment, (bigger duty cycle, more interference). I have been running DSM injectors without resistors using the PWM in megatune. this worked great in fuel only, but it causes lots of noise when spark is hooked up. I put my old stockers back in and PROBLEM SOLVED. I'll be wiring my stock eclipse resistor pack in presently so I can finally run some boost through this engine.

Thanks to kingofl337 for doing a beautiful job on redoing my board mods for me and trying it out on his car, which runs high impedance RX7 injectors.

Victory!

You should ohm out the DSM injectors to make sure one of them isn't shorted.
If one of them is when the MS fires it it could cause the system to reset causing
a missed spark event / injection.

They're all good. 3ohms each.

It will be interesting to see how they run when you put the resistors in line.

So far so good... the car's final challenge is going to be its durability. Wastegate rod end is on its way.

I'm excited... I think I might actually be able to put my glove box back in and stuff that rat's nest of wires under the carpet. I can have a passenger seat again!

Wow, I almost forgot how much fun this car is. And at 0psi!

This really shouldn't have been a problem-- have you discussed it with Lance on the MSEFI.COM forums? If there is such a problem I'd love to get it addressed and make it 'go away' for good... I know alot of people use low impedance injectors without a problems though so it makes me wonder if it's something unique to the Miata, or to your setup, or ???

No, I started a few threads over there asking about it and even asked specifically if it could be the injectors, but I only got a couple replies. natesully tipped me off in a pm over on miata.net. He is also running DSM injectors in his miata, and he is running resistors.

The problem was huge tach spikes/drops.

The problem may have also been grounding issues low imp injector draw alot more current then the OEMs. The factory +12 or the way the megasquirt was grounded could have been the issue.

Sorry to drag an old thread up for the dead, but in my travels accumulating info for my install, I came across this problem (bugger as I was hoping to run low impedance 550s), but also came across this (FAQ 17). Now in my currently quite ignorant state I was wondering if noisy +12V and sensor signals causing MAP spikes could also potentially create noise on the CAS inputs and Al's tach spikes?

Obviously if this is the first thing you checked feel free to call me an idiot.

As a related aside, does anyone know if running resistors inline with P&H injectors increases the injector opening times to similar to that of a saturated injector, therefore negating the advantage of the P&H?