How to MegaSquirt Your Chrysler, Dodge, or Mitsubishi 3.0 SOHC

Overview

This guide covers the 1988–1995 Chrysler/Dodge/Mitsubishi 3.0 SOHC V6 (K‑car derivatives like Daytona, LeBaron, Shadow, Sundance, minivans; Mitsubishi Diamante and trucks). We focus on running the stock distributor and sensors with MegaSquirt.

Applications & Level of Control

  • Engine: Chrysler / Dodge / Mitsubishi 3.0 SOHC V6 (1988–1995).

Distributor Signal Notes (Optical)

The OE optical distributor has two rings. The low data rate ring provides six equally spaced slots (one per cylinder). The high data rate ring is usually 360 slots with 10 consecutive slots missing (360‑10); some variants use four unequal slots. MegaSquirt only needs the six low‑rate slots.

Recommended ECU

  • MegaSquirt‑II (V3.0 or V3.57): native stepper‑IAC control for the stock idle valve. Requires a BIP373 ignition driver to fire the coil (OE module is inside the stock ECU).
  • MS1/Extra: budget option; no stepper‑IAC control from the ECU.
  • MS3: uses the same hardware mods as MS2 for this application.

ECU Modifications — MS‑II PCB V3.0 / V3.57

  • Step 22: install all stepper IAC jumpers (our MS230‑C / MS2357‑C ship this way).
  • Input circuit: build for Hall/Optical input (default on our assembled units).
  • 12 V pull‑up on ignition input:
    • V3.0: solder 1 kΩ between S12 and TachSelect.
    • V3.57: solder 1 kΩ from S12 to JP1 pin 3 (heat‑shrink; underside of board).
  • Enable high‑current coil driver (BIP373 at Q16):
    • Remove any jumper from JS10→IGN (V3.0) or JS10→Q16 center (V3.57).
    • Jumper IGBTIN→JS10 and IGBTOUT→IGN (V3.0). If Q16 not fitted, install a BIP373 with mica insulator.

That’s it—MS2 is ready to drive the coil and the stepper IAC.

ECU Modifications — MS‑I PCB V3.0 / V3.57 (MS1/Extra)

V3.0 highlights:

  • Flash MS1/Extra 029v+; install Hall/Optical input (steps 50A & 52).
  • 1 kΩ pull‑up from S12 to TachSelect.
  • IGBTOUT→IGN to send coil‑driver signal to DB37 pin 36.
  • Remove C12/C30; remove or jumper D1; remove R57 if fitted.
  • Make a 330 Ω + wire pigtail; connect from the top of R26 to IGBTIN; heat‑shrink the assembly.

V3.57 highlights:

  • 1 kΩ pull‑up from S12 to JP1 pin 3 (underside).
  • 330 Ω + wire from the right side of R26 (or U1 pin 7) to IGBTIN.
  • Install BIP373 at Q16 with mica insulator.

Wiring (Distributor & Coil)

  • Coil: negative terminal → DB37 pin 36 (BIP373 output). Positive terminal → switched 12 V as stock.
  • Tach input: optical distributor low‑rate signal → DB37 pin 24.

Optical Pickup Pinout

Pin Purpose
1 Low data rate signal (to MS pin 24)
2 High data rate signal (not used)
3 12V Power
4 Ground

Idle Air Control (Stepper)

  • Chrysler versions use a 4‑pin unipolar stepper; Mitsubishi versions use a 6‑pin bipolar stepper (remove the 12 V feed when wiring the bipolar motor).
  • With MS2, drive the IAC from mainboard pins 25, 27, 29, 31.
  • Pinouts vary across years; early Chrysler usually matches the top diagram, later units the middle diagram. Mitsubishi 6‑wire polarity varies—contact support and we’ll confirm on your vehicle.

Other Functions Typically Handled by the ECU

  • Fuel pump: MS pin 37 → fuel‑pump relay input (formerly from OE ECU).
  • Cooling fan: MS2 can use the on/off IAC output to drive the fan relay. MS1 typically needs an MK‑RelayCtrl.
  • Alternator: OE regulator is ECU‑integrated; retrofit a mid‑’70s Chrysler external regulator, or use MS3’s alternator control.
  • A/C: Can be relay‑controlled without the OE ECU; MS2/Extra and MS3 support compressor control and idle‑up.
  • Tachometer: Often OE‑ECU‑driven—another reason to retain a parallel install. MS1/Extra and MS2/Extra circuits are available if you want to drive it from MegaSquirt.
  • Automatic transmission (41TE): Has its own controller but often talks to the OE ECU—parallel installs are recommended.
  • If sharing sensors with the OE ECU, use caution; giving MegaSquirt its own CLT and IAT sensors is simplest.

TunerStudio — MS‑II

  • Ignition Input Capture: Falling Edge
  • Coil Charging Scheme: Standard Coil Charging
  • Cranking Trigger: Calculated
  • If using MS2/Extra, Ignition Type: Basic Trigger
  • Critical with BIP373: Spark Output = Going High (Inverted)
  • Dwell: depends on coil; start at 2.5–3.0 ms then fine‑tune (reduce to the edge of lean‑cruise misfire, add ~0.2 ms)

If importing a borrowed .msq, match the firmware version or manually copy settings—files are not always cross‑compatible between firmware versions.

Suggested Parts

MegaSquirt‑II V3.0 kit

MegaSquirt‑II V3.57 assembled unit

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