How to MegaSquirt Your Mazda FC RX-7

The mods for using MS2 and MS3 on an RX-7 are more complex than many installs, but the Zeal Engineering Daughterboard simplifies the process. We’ve tested this extensively on RX-7 test cars, making the setup far easier.

Another option is the MS3 with MS3X, which includes rotary support out of the box. In fact, the first production car to run an MS3 was an RX-7.

Applications

  • Mazda RX-7 FC (second generation)

  • First-generation RX-7s converted to FC ignition

  • FD RX-7s (basic setup only – sequential twin turbo control not supported yet)

We recommend:

  • MS2 V3.0 or V3.57 with MS2/Extra firmware 2.1.0+

  • MS3 with MS3X for full rotary support

ECU Modifications – MS2

Zeal Daughterboard Assembly

  1. Install resistors in marked positions.

  2. Install diodes D2–D5 (banded side towards the lower end).

  3. Install capacitors C2, C3, C4, C6, and C7.

  4. Install U1 and U2.

  5. Add Q1–Q4 transistors with orientation matching silkscreen.

  6. Install Q5.

  7. Install C1 and C5 (note polarity).

  8. Add ground jumper near U2.

  9. Wire VR+ and VR– connections correctly.

This completes the daughterboard, which mounts in the case lid.

Using MS-II V3.0 ECU

  • Omit stepper IAC jumpers (step 22).

  • Jumper TachSelect → VRIN and TSEL → VROUT.

  • Add three ignition outputs with 5V pullups:

    • Spark A: 1K resistor from 5V (R24) → D14, jumper D14 → IGN

    • Spark B: 1K resistor from 5V (R28) → D16, jumper D16 → IAC2B

    • Spark C: 1K resistor from 5V (R25) → D15, jumper D15 → IAC2A

  • Omit R19, Q4, Q20, R39, D8 (handled by daughterboard).

Daughterboard → Mainboard Connections

  • 12V → S12

  • 5V → S5

  • GND → Proto GND & SG

  • VR2+ → IAC1A

  • VR2– → IAC1B

  • VR2 Out → JS10

  • IDLIN → R19

  • IDLOUT → D8

  • IN1/OUT1 optional for 1st gen RX-7 FC ignition swaps

Using MS-II V3.57 ECU

  • Set JP1 = 1–2, J1 = 3–4.

  • Remove jumper JS10 → Q16 if installed.

  • Use built-in LED pullups for ignition outputs:

    • PAD1 → PAD16

    • PAD3 → PAD14

    • PAD2 → PAD12

Daughterboard → Mainboard Connections

  • 12V → S12

  • 5V → S5

  • GND → Proto GND & SG

  • VR2+ → PAD15

  • VR2– → PAD13

  • VR2 Out → JS10

  • IN1 → JS11

  • OUT1 → PAD11

ECU Modifications – MS3

Using MS3 V3.0 or V3.57 with MS3X

  • Jumper TachSelect → VRIN and TSEL → VROUT (V3.0).

  • On V3.57, set JP1 = 1–2, J1 = 3–4.

  • Disable JP7 pull-up on MS3X (not needed).

  • For PWM idle on V3.0, install TIP120 mod kit (MK-PWMIAC).

External Ignition Wiring

Stock Wiring → MS Connections

Function Stock Wire MS2 V3.0 MS2 V3.57 MS3/MS3X
NE+ (crank) Red Pin 24 DB37 Pin 24 Main board pin 24
NE– White GND GND GND
G+ (cam) Green Pin 25 DB15 Pin 3 MS3X Pin 32
G– W/B stripe Pin 27 DB15 Pin 4 Main board GND
Leading IGT Red Pin 36 DB15 Pin 10 MS3X Pin 14
Trailing IGT Red Pin 31 DB15 Pin 11 MS3X Pin 33
Trailing Select White Pin 29 DB15 Pin 12 MS3X Pin 15
Tach Signal Black Tach out Tach out Tach out


Settings and Configuration

Ignition Settings

  • Spark mode: Toothed Wheel

  • Trigger angle: 0°

  • Input capture: Rising Edge

  • Spark output: Low (Normal) for MS2, High/Inverted for MS3X

  • Number of coils: Wasted Spark

  • Dwell: 3.0 ms

  • Rotary mode: Enabled

  • Output mode: FC mode

Idle Air Control

  • Uses PWM motor.

  • V3.57: direct control.

  • V3.0: use daughterboard or MK-PWMIAC kit.

Other ECU Functions

  • Fuel Pump: Pin 37 → fuel pump relay

  • A/C: Wire request signal → relay (MS3X can natively control A/C)

  • Boost Control: Boost mod kit or MS3X output

  • Oil Metering Pump: Recommend premix fuel (S5 electronic pumps not supported)

  • Auto Transmission: S4 = standalone, S5 = requires parallel install

What to Order

MS2 Build: