Posting a success story here. I basically built my own MSII from scratch using this forum, pretty much solely, for information. Yesterday, I fired it up and drove it, on the stock sensors.

This post is not to describe my build, but to thank all the forum members that have posted valuable information (Brain, Jason, Joe, etc.). I learned a huge amount and am really enjoying the project. People more often post problems rather than successes.

What worked well:
The Jason CAM/Crank input circuit is awesome.
The Joe spark output mod is also awesome.
Surplus Russian 6-pole triple throw switch allows me to have two "brains" in the car.

What didn't work so well:
Building my own patch cable (ended up buying one that is 10x better than what I could make on the bench).
Serial-USB problems wasted a lot of my time with troubleshooting until I found a cable that worked consistently.

What I would recommend:
This probably goes without saying but do not attempt building a kit from scratch and wire it into your car, unless you can: 1) read a schematic and make intelligent decisions, 2) solder well, and 3) have diagnostic tools like an oscilloscope, multimeter, etc.


Next step is to work with tuning and get it running like stock before moving on to additional hardware mods. Like I said at the beginning, it is currently running on the OEM sensor inputs (which I didn't realize was controversial, or at least contentious). It actually ran pretty well, and I went through all the gears after fiddling around for about an hour. For the future, I want to run vacuum hose to get a MAP signal, and also add a WB.

Anyway, thanks Megasquirt forum!

 

welcome to 2008!

 

What would you build in 2013?

 

I'd like to hear more about how you dropped this 6P3T into your project.

 

As brain would say... Ms3x or bust

 

Thanks for asking. Here are a couple of pics. The person I bought it from claimed it was a surplus switch from a MIG jet. I don't know, but it certainly is sturdy - it has an action like a rifle bolt. It is all metal and ceramic, and, as you can see from the pics, it is pretty large. I put it in an enclosure and tucked it behind the hood release.

The way I have it working is to switch all the injector and spark outputs to the engine simultaneously from one ECU to another. It is a three position, six pole switch. Each pole is used for one of the injector or spark wires. The two injector banks have two wires each, and each coil has one wire, coming from the engine. So, you need six poles. The way I wired it, the first position is the Mazda ECU, the second is null (no output), and the third is the Megasquirt. The ECUs share all other sensor inputs. I don't have a ****, because I was afraid of kicking it and switching while driving.

It has been very useful. For example you can take the back off and tie in an oscilloscope to the contacts to compare the performance of the MS to the factory ECU while the engine is running. Also, if the MS floods the engine for example, I just switch over to the factory ECU to clear the flood.

I imagine for the track, a similar setup could be used to have a back up ECU, or switch between ECUs running different code.