How to MegaSquirt Your Chrysler Hemi Engine

Overview

This guide covers Chrysler/Mopar Gen III Hemi engines used in Dodge Ram/Durango, 300C, Magnum, and Challenger. We focus on fuel and ignition control with MegaSquirt, using factory crank/cam sensors and coils. Drive‑by‑wire (DBW), MDS (cylinder deactivation), and networked body functions remain outside the scope.

Applications

  • Chrysler/Mopar Gen III Hemi: 5.7L, 6.1L, 6.4L (2002+) in trucks and passenger cars (Ram, Durango, 300C, Magnum, Challenger)
  • Level of control: Fuel + ignition (sequential supported with MS3). If retaining factory dash/BCM on a stock Hemi vehicle, keep the OEM ECU in parallel for DBW and body functions while MegaSquirt handles fuel/spark.

Recommended ECU and why

  • Use MS3 + MS3X for native support of Chrysler Hemi crank/cam sensors, sequential fuel/spark, and full I/O
  • Stock Hemi coils do not include built‑in igniters; plan on external igniters (QuadSpark) or an equivalent module

ECU modifications (MS3 mainboard V3.0 or V3.57 with MS3X)

  • Trigger from VR Input:
    • V3.0: jumper TachSelect → VRIN, TSEL → VROUT
    • V3.57: JP1 = 1–2, J1 = 3–4
  • Crank sensor pull‑up (choose one):
    • Internal: V3.57 add 1 kΩ at R57; V3.0 add 1 kΩ from 5 V (proto area) to TachSelect–VRIN jumper
    • External: 1 kΩ between mainboard harness pins 24 and 26
  • Cam sensor pull‑up: enable MS3X JP7
  • Initial trim‑pot baselines:
    • R56 (main hysteresis) and R32 (MS3X hysteresis): fully counter‑clockwise
    • R52 (main threshold): after fully CCW, set ~1 turn CW on V3.57, ~3 turns CW on V3.0
    • R11 (MS3X zero crossing): ~1 turn CW from fully CCW
      That’s it.

Ignition output (QuadSpark recommended)

Use two QuadSpark modules to drive factory coils. Coil mapping (both COP and wasted‑COP use the same output order; set mode accordingly):

  • Spark A → Cyl 1
  • Spark B → Cyl 8
  • Spark C → Cyl 4
  • Spark D → Cyl 3
  • Spark E → Cyl 6
  • Spark F → Cyl 5
  • Spark G → Cyl 7
  • Spark H → Cyl 2

Other vehicle systems (parallel install notes)

  • For OEM dash/BCM/DBW on factory Hemi cars, keep the stock ECU in parallel; MegaSquirt takes over fuel/spark
  • For classic swaps, MegaSquirt can run the fuel‑pump relay and provide a tach output to most aftermarket tachs (use a tach adapter if a stock tach won’t accept the ECU signal)
  • DBW workaround for swaps: a cable‑operated throttle body simplifies integration

TunerStudio settings — non‑VVT Gen III Hemi (MS3/MS3X)

  • Spark mode: 36‑2+2
  • Use cam signal: Yes
  • Cam input: MS3X Cam In
  • Ignition Input Capture: Rising Edge
  • Spark Output: Going High / Inverted (QuadSpark, Bosch 211, etc.). Critical to get polarity correct to avoid module/coil damage
  • Number of coils: Coil‑on‑plug (or Wasted COP if using paired coils)
  • Spark A output pin: MS3X Spark
  • Dwell: start at 2.0 ms; back off until a barely detectable lean‑cruise misfire, then add ~0.2 ms
  • Trigger angle is fixed by this mode—verify with a timing light.

TunerStudio settings — VVT Gen III Hemi (MS3/MS3X)

  • Spark mode: Toothed Wheel
  • Cam input: MS3X Cam In
  • Ignition Input Capture: Rising Edge
  • Trigger wheel arrangement: Dual wheel with missing teeth
  • Trigger wheel teeth: 60
  • Missing teeth: 2
  • Tooth #1 Angle: 693
  • Main wheel speed: Crank wheel
  • Second trigger active on: Falling Edge
  • VVT Settings: set Cam Decoder = “Hemi VVT”
  • Spark Output: Going High / Inverted (QuadSpark and similar)
  • Number of coils: Coil‑on‑plug (or Wasted COP if applicable)
  • Spark A output pin: MS3X Spark
  • Dwell: start at 2.0 ms; fine‑tune as above

Alternative ignition modules

Most external igniters compatible with Hemi coils expect Going High / Inverted (QuadSpark, Bosch 211, AEM DIM, many others). Some CDI systems may require Going Low / Normal—follow the module vendor guidance. M&W Pro‑18 users: wire directly to MS and use falling‑edge ignition mode.

Timing strategy note for Hemi chambers

Modern Gen III Hemi heads burn fast. Typical wide‑open throttle timing requirements are modest; many combos are happy at ~18–20° on pump gas (22° can be excessive). Do NOT start tuning with legacy big‑chamber tables—reduce advance before first fire and verify with a timing light.

Suggested parts (Mopar Hemi + MegaSquirt)

ECU options

Ignition and I/O