Megasquirt 3 Quick Start Guide

Before You Begin

Before powering up your Megasquirt 3 ECU, make sure you have:

• A Megasquirt 3 or MS3-Pro ECU board
• A USB cable (for MS3-Pro) or a serial cable (for MS3 DIY)
• TunerStudio MS Lite or TunerStudio MS installed on your computer
• A 12V power supply or battery
• A wideband O2 sensor and controller (recommended)

Step 1: Wiring Basics

The minimum wiring to power up and communicate with the ECU:

| Pin | Function | Wire Color (typical) | |-----|----------|---------------------| | B+ | 12V Switched Power | Red | | GND | Ground | Black | | USB/Serial | Communication | — |

Important: Always connect the ground wire first, then the 12V power. Never hot-swap connections while the ECU is powered.

Step 2: Install TunerStudio

1. Download TunerStudio MS from tunerstudio.com
2. Install and open it
3. Create a new project and select your MS3 firmware version
4. Connect to the ECU via USB or serial port
5. If connection is successful, you'll see real-time data on the dashboard

Step 3: Basic Configuration

In TunerStudio, configure these essential settings first:

Engine Constants

• Number of cylinders — match your engine
• Injector size — in cc/min (check your injector specs)
• Engine type — even fire or odd fire

Fuel Settings

• Required fuel — TunerStudio calculates this based on engine displacement and injector size
• Control algorithm — Speed Density is recommended for most setups

Ignition Settings

• Spark mode — select based on your ignition type (wasted spark, COP, distributor)
• Trigger wheel — configure to match your crank and cam sensors

Step 4: First Start

1. Prime the fuel system — cycle the key a few times to build fuel pressure
2. Check for errors — look at the TunerStudio error indicators
3. Crank the engine — it may take a few attempts with the initial fuel map
4. Let it idle — adjust the idle target RPM and idle valve settings
5. Monitor AFR — your wideband should show roughly 14.7:1 at idle

Next Steps

Once the engine is running:

• Configure your wideband O2 sensor for EGO correction
• Set up acceleration enrichment for smooth throttle response
• Configure coolant-based warmup enrichment
• Begin VE table tuning on a dyno or with road tuning

Reference Documentation

The official MS3 documentation is available at msextra.com:

• Setting Up Manual (PDF)
• Hardware Guides for specific board versions
• TunerStudio Reference Manual