Build Guide for Megasquirt from Kit
 

If you've spent more than 5 seconds on this forum you should know about trubokitty.com by Braineack which shows in excellent detail the process of building the MS3X from the diyautotune kit. I recently went through the whole process and filmed it to provide a video companion to the written instructions. All the credit is to Braineack obviously but I figured if you were new to a soldering build of this size like I was, actually seeing it may be helpful. I have a new channel on YouTube which is 90% Miata related. I'm not selling anything, just trying to give something back to the community. Whenever I work on the car, I try to whip out the camera and narrate a bit.

The first three parts are out now (an intro, the main MS3X build, and the PNP harness build). Upcoming videos will show the install, initial setup, and some tuning.

I tried to keep the length down but still show a lot of detail. Let me know how I did balancing that. :)

Here you go, please enjoy.

Intro:
Main Build:
Plug and Play Harness:

Parts 4 and 5 are up: Edit - Part 6 also!




Edit: Now with Part 7


Hey, check out the new thread for my second series on Tuning with Tuner Studio:

https://www.miataturbo.net/megasquir...g-guide-98277/

Where is your WB sensor screwed in?

​​​​​​
Mine is in the stock location mostly. I have an after market header so it's just a bit lower than oem. My wb controller has a narrow band simulator which is what I connected to the stock wiring. I ran it that way for a couple of months with no problem. The wb signal goes straight to the ms3x harness.

I have a video on that install also. :)

Where's that video?

How did you connect the NB signal to the MS—tap into the wire at pin 2N on the OEM connector? Why not just run the wire to the signal wire on the OEM connector by the CAS?

very neat videos

I set it up so the stock ECU would work without messing with wiring. My NB02 output goes into the OEM connector by the CAS as you say. The WB output goes into the cabin and into my MS wiring harness. The MS harness connects between the stock ECU connector and the DB37 connectors on the MS. But the OEM side I leave the 2N pin blank (ignored) because that's the NB signal which the MS doesn't want. The wire in the MS harness that normally goes to that in I left free and connected it instead to the WB wiring coming into the cabin from the controller. This signal also goes to the gauge in my center console. There are two grounds on this controller (Spartan 2 from 14point7). Sensor ground is the same as sensor ground on the MS. Heater ground is the chassis ground. The MS reported value and the gauge match exactly this way.

Is there any reason you couldn't just swap the WB signal wire in for the NB signal wire (at the connector by the CAS) when you plugged in your MS?

Not really, that's fine and probably most do it that way. I set it up with two paths so there's less to change if I needed to go back. Like to pass smog checks or something.

I just posted Part 6 (up above on post 2) which covers the firmware load, tuner studio general set up, initial timing, and first start.

I think this is the last one for the build guide but I do have some stuff recorded for idle tuning. I'm going to get that organized a little better and post that, probably under a new series.

Thanks for the comments and cats! It does motivate me a lot.:bigtu:

I also noticed that you hooked up the WB power and ground to the OEM power and ground locations at the sensor harness, whereas many folks and WB makers say to connect to the power and ground at the ECU.

It ends up being the same thing. Oem (harness) sensor ground is the same as ms sensor ground and same for heater ground (chassis ground). I checked with an ohmmeter. At least on my 94. The key is if the MS afr in tuner studio matches your gauge, you're all set.

Even though the grounds may be connected, the connections between them are not zero ohms of resistance but some small finite value. Therefore, when any current flows across the connections, it creates voltage offsets. This is the reasoning for using different ground paths for heater and sensor circuits.

Sure. Always check with an ohmmeter. Also that's one reason I got the wideband I did rather than innovate... Because innovate went to a single ground which seems lame.

I finally got series 2 out -- I posted a few vids for basic tuning in Tuner Studio, starting with covering Idle. New thread:

https://www.miataturbo.net/megasquir...g-guide-98277/

Cool videos. Also, I like your idea on how you wired in your wbo2 signal. I want to set up my 97 so I can just swap the ecu,injectors, wire open wg, and install the MAF to pass smog. Leaving the stock NBo2 and WBo2 in the downpipe and not having to mess with wiring or removing the sensors.

These videos are great. What I'm still confused about having watched these and read through the trubokitty site more times than i can count is, whats the deal with the wires that were hooked up to the stock ECU that aren't used in the megasquirt. I'm specifically talking about the 99-00, however every year group has wires not used for the megasquirt. Are they just not needed, or are people leaving the stock ecu in to handle body control?

They are mostly ignored in the megasquirt. I say mostly because some people may use a wire here or there for something else but no one is using the oem ECU for other control. I'm not sure about the NB but in the NA the ignored wires are for egr, the evap solenoid, narrowband o2 sensor, etc.

You'll be ok if you follow the trubokitty wiring map.

Thanks for that. It mainly seemed like there were various 12v inputs and auxiliary outputs for things ive never head of, like PSP switch.

That one is like power steering related, right? Like you can use it to idle up when the power steering is fully engaged or something. Not sure if that's right, but if so you could actually put that in if you wanted. But I don't think it would be a big deal, definitely not required.