How to MegaSquirt your Mazda Miata

Updated 2/12/2008 --Updated with release info on 1996-1997 MSPNP

Also-- if you haven't already, please read the 'disclaimer' at the top of the parent page here.

This documentation is for using the MegaSquirt-N-Spark Extra firmware version 029v or later.

Email me if you find anything that needs to be updated.

Preface-- For the DIY'er, the article below will get you there. 

For those of you interested in a very polished Plug-N-Play solution check out our new MegaSquirtPNP for the 1990-1997 Miata.   www.megasquirtpnp.com is the informational site, and they are available here.

On to the DIY 'How to MegaSquirt your Mazda Miata' article....

Application: 1990-1997 Mazda Miata, or later models by swapping in the 90-97 CAS

Level of control:  Full Standalone EMS-- Fuel and Ignition Control

Tach Input Background:  Crank Angle Sensor (CAS) Wheel in the 90-97 Miata

There are two 'sets' or 'rings' of holes in the optical CAS.  The outer ring of holes is read by an optical sensor and then sent across a wire to the ECU and referred to as the CKP signal.  Likewise the inner ring with only one hole is also read by an optical sensor, sent across a wire to the ECU and is referred to as the CMP signal. 

Outer Ring    -     Crank Angle Sensor (RPM)  -  CKP

Inner Ring    -     Top Dead Center Sensor   -   CMP

Getting the Tach Input Signal:

Run MSnS-E and the "2nd Trigger" Wheel Decoder option (where the missing tooth on the wheel decoder comes from a second sensor, usually cam position).  The CAS has a CMP and CKP signal, so you take the outputs of each and run them into the MegaSquirt.  Take the CKP signal (4 holes in the Optical sensor wheel, the "outer" ring of the CAS), and run it to the primary tach input on the MS with a 12v pullup resistor - then you take the inner ring of the CAS (1 hole in the sensor wheel) and run it to the secondary tach input on MS (it's pin 11 on the MS-I cpu) with a 5v pullup resistor. 

If you follow my documentation for the mods below you'll externally wire the tach inputs like this:

The Primary tach input (CKP) (Reported to be White on Miatas) is connected to pin 24 on the MegaSquirt's DB37

The Secondary tach input (CMP) (Reported to be Yellow on Miatas) is connected to pin 25 on the MegaSquirt's DB37
 

If you're using a relay board:   Pin 24 goes through to position 15, Tach/Ignition for the CKP/Primary Tach Input.  Pin 25 goes through to position 7, S1 for the CMP/Secondary Tach Input.  You'll need to make sure your relay cable has this wire in place, if so then this will work fine.  All of my MS-II ready relay cables have this wire in place. (black loom covered cables are MS-II ready, old MS-I grey cables do not have this wire)

-How to mod a MegaSquirt-I PCB2.2 ECU-

Parts Needed for Input Mod:  (1) 1k 1/4w Resistor and (2) 470 ohm 1/4w Resistors   (Grab a mk-pullup with your order to get the resistors you need for next to nothing!)

"CMP Signal" -- Lay a 1k 1/4watt resistor across the bottom of the PCB with one end at pin 11 of the processor (U1) and the other end at the X11 hole.  Bend the resistor leads to raise the resistor just a bit off of the PCB and allow a lead on one end to drop through X11 and solder that end in place (while making sure the other end is in place near pin 11 still, and with the resistor still raised a bit off the board so the leads don't short against anything).  Then use needle-nose to hold the resistor lead to pin 11 and solder it to the pin.  Now to get the 5v pullup use a 470 ohm 1/4w resistor and solder one end of it to the first resistor at X11 (just tie them together) and the other leg of it to the small unlabeled hole just above and to the right of D9 (when looking at the PCB from the top that is). Do not connect to the leg of D9 itself - you will be using a small hole in between D9 and R13.  Once again raise this just enough off of the PCB to prevent it from shorting with any of the leads sticking out on the board. (Heatshrink tubing over the whole wire/resistor assembly works nicely)

The new "cap mod" turns this into a low pass filter that helps avoid misfires caused by a noisy CMP signal. Solder a length of wire to a 0.1 uF capacitor, and connect this capacitor-on-a-wire between pin 11 on the processor and a ground point. The second hole from the bottom on the JP1 header is a good ground point.

"CKP Signal" -- We just need a 12v pullup.  Install a 470ohm 1/4w resistor between the right side (non-band) end of D5 and the right hole (banded) end of D9.

-How to mod a MegaSquirt-I PCB3.0 ECU- 

First off when you build up the PCB3.0 board configure the tach circuit for Hall/Opto/Points (step 52). When you get to optional components that say to only install them if you are triggering from the negative side of the coil;  you aren't -  so don't.  Note that normally my pre-assembled MegaSquirt-I ECUs (MS130-C) are assembled and loaded with the standard B&G fuel only firmware, which means they are configured for a fuel only install to trigger from the negative side of the coil.  It's easy to reconfigure them, click here for how.

Parts Needed for Input Mod:  (1) 1k 1/4w Resistor and (2) 470 ohm 1/4w Resistors  (Grab a mk-pullup with your order to get the resistors you need for next to nothing!)

"CMP Signal" -- Lay a 1k 1/4watt resistor across the bottom of the PCB with one end at pin 11 of the processor (U1) and the other end at the IAC1A hole.  Bend the resistor leads to raise the resistor just a bit off of the PCB and allow a lead on one end to drop through IAC1A and solder that end in place (while making sure the other end is in place near pin 11 still, and with the resistor still raised a bit off the board so the leads don't short against anything).  Then use needle-nose pliers to hold the resistor lead to pin 11 and solder it to the pin.  Now to get the 5v pullup use a 470 ohm 1/4w resistor and solder one end of it to the leg of the first resistor to IAC1A and the other leg of it to the 5v+ hole just above the proto area.  (This is a long reach so you'll need to use a bit of wire to get across the board.)  Once again raise this just enough off of the PCB to prevent it from shorting with any of the leads sticking out on the board.  (Heatshrink tubing over the whole wire/resistor assembly works nicely)

The new "cap mod" turns this into a low pass filter that helps avoid misfires caused by a noisy CMP signal. Solder a length of wire to a 0.1 uF capacitor, and connect this capacitor-on-a-wire between JS8 and SG or a ground hole in the proto area.

"CKP Signal" -- We just need a 12v pullup.  Install a 470 ohm 1/4w resistor between the right side (non-band) end of D1 and the left leg (banded end) of D9.

Click for a larger view (does not show cap mod)

Taking Control of the Ignition --

Decision time-- use the stock ignitors or use dual BIP373 coil drivers.  I'm going to document both options for you here, but I'd recommend using the stock ignitors as it's simpler, and they will properly trigger your tachometer.

Only use one method or the other for spark output, don't try to combine the two!

Option 1: Spark Output to factory Miata ignitors:  (Recommended)

Option 2: Spark Output to MS-internal BIP373 Coil Drivers: 

Things to be careful of:

IF USING THE STOCK IGNITORS: 

When the MS is powered off, it's spark triggers are grounded.  So you MUST make sure the MS is powered on if the coilpacks/ignitors are also powered on!  During installation, it's common to have the MS attached to the ignitors, and have the ignition key "on," but not have the MS powered up yet.  So I make sure I do power and grounds first to the MS, and attach the spark outputs LAST before I am ready to start the car.
 
You'll know you're doing it right if the "power transistor"  (a.k.a. the ignitor) is not too hot to the touch.
 

IF USING THE BIP373 IGNITORS:  

In MegaTune's Ignition Settings, 'Spark Output Inverted' must be set to YES.  And you should enable Dwell Control.  Skipping either of these will cook your BIP373's, and possibly your coils.  (more info on MegaTune setup below).

What about everything else???

Most of my 'how to' articles focus on the ignition system control, that's because the rest of the sensors and injectors are pretty much the same for every car out there, with only minor differences that are well covered in the MegaManual.  The tricky part is taking control of the stock ignition system so that's what we focus on covering for you here.  For everything else you'll find the MegaManual at www.megasquirt.info will cover you very well.

MegaTune Configuration

You need to use a timing light to calibrate the MS's timing to the Miata's timing.  To do this, run "fixed angle" of 10-15 degrees and adjust the "trigger angle" until the timing light flashes while the motor is on the same 10-15 degree mark on the crankshaft, this needs to be spot-on.  This way, whatever timing Megasquirt is commanding is actually happening. 

Here are some example settings for an early 90's Miata that I got from 'Aussie Driver' on the www.miataturbo.net forums.  These should get you very close if not right on.....
 

NOTE:  The above 'Spark Settings' page has Spark Output Inverted set to NO.  Based on the 199-1995 cars when using the mods described on this page.  If you are using different ignition modifications that what is described on this page these settings may need to be different.  Proper dwell settings are very important as well.  Again, if you're using the ignition mods described in this page, the dwell settings below should work well for you. 

Dwell settings for 1.6 liter coils in the 1990-1993 cars:

Dwell Control:  Dwell Control
Cranking Dwell: 8 ms
Running Dwell: 5 ms

Dwell settings for 1.8 liter coils in the 1994-1997 cars:

These coils charge faster and need slightly less dwell than the 1.6 coils.

Dwell Control:  Dwell Control
Cranking Dwell: 7.5 ms
Running Dwell: 4.5 ms

Base Fuel and Spark maps

Here are 'Aussie Driver's fuel and ignition maps setup for an NA car.  These should only be used as base maps and tuning will be required for your car!  Do not just load these and go for a WOT run!

Miata Ignition Advance Map in .vex format

Miata Fuel Map in .vex format

PWM IAC Settings for use with the TIP120 (as comes in our little modkit here)

For 1990-93 cars, other years may be different and the wrong settings can damage your IAC valve

These settings were carefully selected on a vehicle using a scope, and daily driven for a couple of weeks.  They should work pretty well for you.  If you're using a different transistor the 'Idle Valve Frequency' remains the same as that's tied to your IAC valve's needs, the 'Cranking DC' and the two 'Idle duty at temp (dc)' settings will be different.  I'll tell you though, setting these with a scope is easy, setting them by guessing numbers can drive you crazy.  The good news is if you're using a TIP120 the settings below should just plug in and work perfectly for you.

Important note when performing firmware flashes/upgrades!

Be sure to disconnect your coils / ignitors before upgrading firmware. If you don't the MS will hold the lines high, and your coils or ignitors will blow up.  After flashing the firmware, configure all of the important ignition settings and then you can reconnect the coils / ignitors.

This is as simple as unplugging the ignitor(s), flashing the firmware, reloading your .msq file, and then (with the power off) plugging your ignitor(s) back in. 

______________________________________

Check out our 91 Miata Turbo project car at this link.

Click Here if you have questions or would like to contact us!