How to MegaSquirt Your Mitsubishi 4G37

Overview

This guide covers the 1990–1994 Mitsubishi 4G37 1.8L SOHC (Eclipse/Talon/Laser base models). The stock distributor uses an optical trigger with an outer ring of four equal slots (CKP) and a single inner slot (TDC/CMP). For distributor ignition you only need the four‑slot outer ring. AMP EFI / DIYAutoTune MegaSquirt ECUs provide full standalone control of fuel and ignition on this platform.

Applications & Level of Control

  • Engine: Mitsubishi 4G37 1.8 SOHC (’90–’94 DSM base models).
  • Control: Full standalone EMS — fuel & ignition.

Optional: Distributorless (advanced)

You can convert to wasted‑spark by swapping to a 4G63 coil pack and using the 4G63 ignition mods. In that case specify 4 trigger‑wheel teeth (instead of 2) and enable dual distributor output for wasted spark.

ECU Options

  • MegaSquirt‑II (V3.0 or V3.57)
    • Stepper IAC capable
    • Uses BIP373 for direct coil control

MS2 (PCB V3.0 / V3.57) — Required Mods

  • Build for Hall/Optical input (default on our MS230‑C units).
  • 12 V pull‑up on ignition input:
    • V3.0: 1 kΩ from S12 → TachSelect.
    • V3.57: 1 kΩ from S12 → JP1 pin 3 (underside, heat‑shrinked).
  • Enable the IGBT high‑current coil driver:
    • Remove any JS10→IGN (V3.0) or JS10→Q16 center (V3.57) jumper.
    • Jumper IGBTIN→JS10, and IGBTOUT→IGN (V3.0).
    • If Q16 is empty, fit a BIP373 with mica insulator.

That’s it — MS2 is ready to directly drive the coil and manage ignition.

Wiring

  • Coil (no built‑in module): negative terminal → DB37 pin 36; positive terminal → switched 12 V (same source as OE ECU).
  • Distributor CKP (outer ring) → DB37 pin 24.

Wire Colors (typical 4G37 distributor)

Wire color Purpose
Black / White 12 V power
Black Ground
Brown / Yellow CKP signal (to MS pin 24)
Blue TDC/CMP (not used for distributor ignition)

Idle Air Control

4G37s use a DC servo idle motor; aftermarket ECUs do not control these. If you want ECU idle control, retrofit a PWM valve or a stepper valve (MS2 only) and wire accordingly.

Other Systems

  • Fuel pump: MS pin 37 → fuel‑pump relay (replaces OE ECU control).
  • A/C: Can be run with a simple relay (A/C request → compressor relay). Not factory‑tested here.
  • Fans, cruise, and most transmissions on these cars operate independently of the ECU.

TunerStudio Setup — MS2

  • Ignition Input Capture: Falling Edge
  • Coil Charging Scheme: Standard Coil Charging
  • Cranking Trigger: Calculated
  • MS2/Extra Ignition Type: Basic Trigger
  • With BIP373: Spark Output = Going High (Inverted)

Suggested Parts (DIYAutoTune / AMP EFI)

Legal/Emissions: For off‑road/closed‑course use where required. Verify local compliance and any warranty impacts before modifying engine controls.