MS3x Flyback diodes
 

I am currently putting together a wiring harness following Frank's guide for my 97. Only thing I am doing differently is a external wire harness.

I am confused by the step "Install a 1N4001 with the banded side to 12V and the other side to the idle output of the MS3X (pin 9)"
Is the 12V source another pin on my connector? I read a few threads of people asking similar questions but they didn't really make sense, I am not the brightest when it comes to this and was hoping someone could make it really clear for me.

My thought is that it goes the end of the wire is attached to pin 9 (for this one) and in the middle of the wire is the 1N4001 with the unbanded side facing pin 9 and the other side facing a pin on my tyco connector, which pin I am not sure.

Any help would be appreciated, thanks!

It is a tad confusing, especially since there are many different versions of 12v inside the case.

This instruction dates back to when the idle circuit was typically constructed on the main board of an MS1 using stone-age components. And, frankly, there are too damn many different sets of instructions out there...

Looking at the MS3X schematic, a part of me wants to say that the circuit is already adequately clamped internally.

But if you want to be cautious, the only clean way to install this flyback diode is to put it outside the case. In other words, splice it into the wiring harness itself, between the idle wire (blue / orange) and the 12v supply wire (white/red).

That said, I install no such diode when I do an MS3Pro install. And given that the MS3P design is basically just a cherry-picked amalgam of all the best schematic elements of the Microsquirt, the 3.57 and the MS3X, I suspect that its idle circuit is identical to that of the 3X, meaning that the 3X doesn't really need additional flyback protection on the PWM outputs.


TL;DR: Ignore this. Move on.

So all that effort trying to figure out what it could be for nothing?? :rofl:
I suppose on the bright side it will be a lot easier this way. Thanks for the reply !

The diode is for idle and boost control. Just install between 12v (one of the wires going to the idle/ebc that isn't going to the MS) and the other wire from MS. At least that is how I understood it. When I didn't have the diode installed my idle valve was going craycray.

Yeah, but which MS was this with?

You gotta consider the purpose of the diode vs. the underlying circuit topology.

With the stock ECU, no external diode was needed, because the stock ECU is well-designed (from a hardware standpoint) and was internally clamped on all PWM drivers.

The MS1/2, for all their achievements, always suffered from shitty hardware design. The core ECU was intended to drive an 80's vintage Chevy with a distributor and TBI, and everything beyond that was community-contributed hacks. They worked, but they tended to be half-assed. Like the wasted-spark ignition driver that caused key-on backfires and destroyed your coils if you forgot to unplug them before doing a firmware update, for which I had to design the JoeSpark mod to correct.

This flyback diode was a workaround for a sub-optimal IDL driver circuit in the community-made MS1/2 / r3.0 implementation. The newest hardware designs are finally starting to get, well... pretty damn good.


Give it a shot. If it totally fucks everything up, then I was wrong. But I think it'll work. The MS3X is actually one of the better-designed aftermarket ECUs out there, aside from the moronic, brain-dead, uncle-fucking, testicle-shitting rectal wart of a CMP (VR2) input circuit.

I'm using an MS3x. This is what I understood was the issue:
https://www.miataturbo.net/megasquir...le-duty-61914/

The MS3X/Pro idle circuit requires different software settings vs. the broke-ass old MS1/2 circuit.

This surprises you?

Either you are reading it wrong, or I am. Since I know next to nothing about electronics, and it's basically what you do, it's probably me.

I thought what that thread is saying, is that with the MS3x you need to add the flyback diode because if you don't the duty cycle is too high and makes the valve noisy. This is exactly what happened to mine.

That is correct. Add the diode to get the duty cycle in the correct (lineair) range of the valve.

Correct.
12V is the W/R wire in the Tyco connector.

the expander board for the MS3 has shit flyback and needs diodes added.

the ms3pro doesnt.


I use the same tune from my ms3x (with diodes) that I do on my ms3pro.

Fair enough.

Yet another reason why I wish B&G and DIY would publish the fucking schematics for their devices. So that we could answer questions like this definitively, rather just just saying "Durrrr, I dunno."

basically the expander uses a more complicated flyback system but it is unable to handle the massive juice that is the miata. Mine went totally koo koo when I added VVT. Once VVT would activate, all outputs on the expander would simply stop working. I discovered this because my tach was one of them and would drop to zero or swing around like a nutjob.

So, the consensus is: if it is an MS3/MSx use the diodes... That is my understanding.

The consensus is: if you're using nitrous 1, 2, ebc, idle, vvt off the expander, use a diode on those outputs.

The flyback diodes on the (3) 9022Gs go to ground instead of 12v; this doesn't work.