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MegaManual Index -- MegaSquirt Features -- The Development of MegaSquirt® EFI Controller
What you NEED to Install MegaSquirt -- Purchasing a MegaSquirt -- About this Manual

Introduction to the MegaSquirt® EFI Controller

The MegaSquirt® family of EFI controllers (including MS-I™, MS-II™, MicroSquirt®, and the MS-II Sequencer™) is a series of experimental Do-It-Yourself universal programmable electronic fuel injection controllers for spark ignition, liquid fuelled internal combustion engines. Experimental means that YOU will be responsible for sorting out some details of your fuel injection that are specific to your application and equipment. In order to assemble, test, and install and safely use MegaSquirt® EFI Controller, you must read, understand and follow this manual.

MegaSquirt® EFI controllers are not for sale or use on pollution controlled vehicles. Check the laws in your jurisdiction to determine if using a MegaSquirt® EFI controller is legal for your application.

In general, there is a lot of assistance available on the MegaSquirt® EFI controller Forums Web site, in this manual, and on the MegaSquirt® EFI controller FAQ, but ultimately YOU are responsible for the safe and reliable construction and operation of your electronic fuel injection system and its components, including the MegaSquirt® controller. Before doing anything else, be sure to read and understand all applicable safety precautions for your vehicle, tools, and equipment.

The MegaSquirt® family EFI controllers are designed by Bruce Bowling and Al Grippo. In order to assemble, test, and install and safely use MegaSquirt® EFI Controller, you must read, understand and follow this manual.

MegaSquirt® Features

The MegaSquirt-I™ EFI Controller uses an 8 MHz Motorola 68HC908 processor and a Motorola MPX4250AP MAP sensor to provide electronic fuel control. MegaSquirt-I™ is based on the Motorola MC68HC908GP32 Flash-based microcontroller operating at an internal bus speed of 8 MegaHertz (this is bus speed - remember that most microprocessors specify their parts at external crystal speed, which is then divided down by four to yield internal bus speed). MegaSquirt-II™ EFI controller upgrade uses a 24 MegaHertz HC9S12C32 processor.

Many OEM and popular aftermarket EFI systems use older processor technology (like the MC68HC11 or Z80) that operates at 1 or 2 MHz internal bus speed. The MegaSquirt® EFI Controller has a faster clock speed, coupled with direct assembly language programming, which give the MegaSquirt® EFI Controller its power.

MegaSquirt-II™ Controller:
MegaSquirt-I™ Controller:

All of the embedded microprocessor code executed by MegaSquirt-I has been hand-written directly in assembler, not compiled from a high-level language, such as C. Working directly in assembler produces the most efficient and fastest-executing code possible. The result is that the MegaSquirt® EFI Controller can provide real-time fuel calculations up to 16000 RPM! As well, the assembly code for the MegaSquirt® EFI Controller is available on the MegaSquirt® EFI Controller web site, for anyone who wishes to view or customize it. A freeware compiler is available at that site too, so there are no extras to buy.

MegaSquirt-II™ code is written in C, and the freeware GCC compiler is available for you to write your own code or modifications. MegaSquirt-II™ adds ignition capabilities (including missing tooth crank wheel support), as well as much higher fuel pulse width resolution, stepper motor IAC control, and a number of other features you can read about in this link.

Additionally, the on-chip Flash memory makes either MS-I™ or MS-II™ EFI controllers use processors that are a true single-chip set-up, reducing cost and extending reliability. Also, using Flash technology allows the instant re-programming of constants, enrichments, etc. while the vehicle is running. The processor can even be re-loaded with other control code using a simple programming interface and no additional hardware. The flash can be re-written at least 10,000 times, and it has a retention duration of 20 years.

Commonly available (from General Motors) coolant and air temperature sensors are used as default sensors, though you can substitute others. The MegaSquirt® EFI Controller provides either speed-density or alpha-N fuel control. The MegaSquirt® EFI Controller uses dedicated tuining software for firmware reprogramming, engine monitoring, and tuning. Even without a computer connected, the three LEDs on the MegaSquirt® EFI Controller enclosure allow you to monitor injection pulse [commanded], warm-up enrichment, and acceleration enrichment at any time.

The MegaSquirt® EFI Controller microprocessor code is available, and you are encouraged to make and share modifications (for use on B&G boards) to suit your installation. Several modified versions have been developed for particular applications/features already. Other people have developed and shared helpful freeware for MegaSquirt® EFI Controller, including:

In addition, ancillary hardware has been developed, or is being developed, for your MegaSquirt. These include:

  • As well, Jim Willette has developed the Willette programmer - for programming blank or corrupted MegaSquirt-I™ processors, and a MegaProgrammer(.ZIP file) is also available for the same purpose.
  • The best feature of some MegaSquirt® controllers is that you build them yourself! Since you assemble the controller, and all information about the design is available to you, you are able to troubleshoot the board if a problem arises, and, in almost all cases, repair the unit yourself. The system as it exists today is a complete “turn-key” solution. You solder it together, install in the vehicle or boat, tune, and use it. The complete source code is available for those who want to understand or even modify the control algorithms.

    The Development of MegaSquirt® EFI Controllers

    The MegaSquirt® family of EFI controllers came about because of the apparent need for an inexpensive, “turn-key” fuel injection controller by many individuals. Bruce and Al had design and offered the EFI332 system for Do-It-Yourself EFI enthusiasts. The hope was that theEFI332 project would result in a system that could ultimately be used for all applications, and this was one of the main reasons for offering their 4-layer MC86332 board as the EFI332 platform in 2000.

    However, relatively few EFI332 systems had been built and installed on vehicles at first. We feel that one of the main reasons for the small number of operational systems was due to the complexity of the current EFI332 system. One has to be both a hardware and software expert, install and learn a bunch of software development tools, write embedded code, and become an expert in engine control algorithms. The EFI332 system is very powerful and flexible, but requires a tremendous learning curve, a wide range of skills, and many hours to install successfully. Bruce and Al thought that there is another group of people out there who want an EFI system in a more complete and turnkey state, and somewhat simpler. This was the idea behind the MegaSquirt® EFI controller.

    The philosophy for the MegaSquirt® EFI controller system is simple: provide a controller for fuel injectors which can be adapted to any application, without having to write embedded code or understand the details of engine controls. In addition, the plan has been to publish the schematics, software, algorithms, etc. to everyone to enhance the MegaSquirt® EFI controller's potential as an educational project. This is not a commercial unit, but an experimental unit directed at Do-It-Yourself applications for people who want to learn about electronic fuel injection control systems.

    An early version of the MegaSquirt-I™ EFI Controller was described in Circuit Cellar magazine in an article titled "Building a Fuel-Injection ECU" by Bruce and Al in January 2002.

    The MegaSquirt-I™ EFI Controller uses a flash-based Motorola microprocessor (MC68HC908GP32) for the calculation of fuel pulse width and injector control. Additionally, host software (Windows-based) was developed which allows the run-time adjustment of control parameters.

    In 2005, MegaSquirt-II, a replacement daughtercard for the MegaSquirt-I™ EFI Controller's 68HC908 processor became available from Bowling and Grippo. This daughtercard included a much faster processor and increased memory, and also included control options for stepper style IAC controllers and ignition systems. All but the earliest version of MegaSquirt-II™ are CAN (controller area network) enabled, allowing them to 'talk' to add-on modules such as sequential injections drivers and transmission controllers.

    The MegaSquirt® EFI controller uses standard sensors (coolant temp., intake manifold air temp., throttle position, oxygen, and trigger from existing ignition system) to perform batch fuel injector (two banks) pulse width control. Not having ignition control makes this an ideal unit for replacing a carburetor - you can keep your existing ignition.

    What you NEED to Install a MegaSquirt® EFI Controller®

    The MegaSquirt® EFI controller is a universal electronic fuel injection controller that can be made to work on any spark ignition internal combustion engine, with the right external parts. However, the success of your installation depends on YOU. In order to make the MegaSquirt® controller work on YOUR car, boat, chainsaw, or whatever, you will need:

    Installing the MegaSquirt® controller in a vehicle that already has EFI means you will need to consider how you will run the ignition and any other devices the OEM ECU controls [such as the transmission, speedometer and other gauges, and emissions devices], how you will interface the MegaSquirt® EFI controller to your existing wiring harness, and whether you can reuse your existing sensors.

    Do YOU have enough knowledge, skills, money, and energy to complete your installation? The MegaSquirt® EFI controller is the fuel injection controller only, and YOU will have to figure out everything else you need for your vehicle. This manual covers much of the specific information you need for the MegaSquirt® controller, and general guidelines for things like fuel systems, etc.

    A good book on OEM and aftermarket electronic fuel injection systems is Fuel Injection: Installation, Performance Tuning, Modifications by Jeff Hartman (1993). It is published by Motorbooks International [ISBN 0-87938-743-2]. Other references can be found here.

    You will not be dealing with your MegaSquirt alone, however. Thousands of MegaSquirt® kits have shipped. There is a huge amount of collective experience and knowledge related to the assembly and installation of the MegaSquirt® EFI controller in various vehicles available on the MegaSquirt® Forums web site.

    What You Do NOT Need

    Purchasing a MegaSquirt® EFI Controller

    You can buy complete kits (which include everything - the PCB, programmed processor, all required electronic parts, along with the case, etc.) from The MegaSquirt® EFI controller distributors that accept various forms of payment. These distributors have been essential to growth and support within the MegaSquirt community. Be SURE to check the Products and Services forum on for information on the reputation and service of particular distributors before ordering. In general, you should be very cautious of distributors not listed below.

    MegaSquirt® EFI controllers are not for sale or use on pollution controlled vehicles. Check the laws in your jurisdiction to determine if using a MegaSquirt® EFI controller is legal for your application.

    Offers the full line of Bowling and Grippo's MegaSquirt® Products as kits or fully assembled and ready for use. All kits are fully labeled, including everything you'll need to build your own unit. Additionally carries wideband o2 systems and other tuning products that integrate nicely with your MegaSquirt® Engine Management System. Same day shipping on in-stock orders received by 2pm EST.
    is Philip Ringwood's site (one of the authors of the MSnS-Extra code) dedicated to UK and European based sales of fully assembled and tested MegaSquirt® ECU's running the MSnS_Extra code. The ECU's include a wiring harness, RS232 communication cable and the relevant software / drawings, etc.
    EFI Source
    is dedicated to supplying the highest quality EFI products to the performance minded automotive community. Our goal is to make programmable EFI systems affordable to everyone without sacrificing quality or functionality. We will constantly be adding new products in order to meet this goal.
    offers a line of fully assembled, developed and integrated MegaSquirt® engine management packages for VW, Audi and other import vehicles. Each KPTuned MegaSquirt® ECU is specifically modified for the intended installation with all additional circuits installed, a custom wiring diagram provided, pre-configured software and vehicle start-up support available. Wiring, installation and tuning services are also available on site upon request.
    A MSBR © a casa da MegaSquirt no Brasil. Seja bem vindo e tenha acesso ao que existe de melhor no mundo a presos nacionais. Venha nos conhecer!
    PSM Competicion
    Distribuidor Oficial Megasquirt en Argentina, Buenos Aires. PCB´s Originales B&G, los únicos con soporte técnico post venta y amplia experiencia en el rubro. Nuestras Megasquirts originales salen 100% testiadas y con garantia local, tambien ofrecemos el servicio de instalación , reparación y puesta a punto de ecus programables megasquirt y otras. Somos un punto de venta para otros productos relacionados con la competición como bujería, volantes de acero, depósitos de venteo, intercoolers, watercoolers, inyectores, widebands, mangueras siliconadas entre otras.

    PSM Competicion banner
    ( )
    Pirata Motor
    Distribuidor oficial de MegaSquirt España, asesoramos y ayudamos de forma personalizada en la instalación, configuración y ajuste de tu proyecto, para ello disponemos del KIT sin montar o proporcionamos la ECU totalmente montada y preparada para el arranque. Disponemos de las herramientas necesarias para el ajuste y de todo lo necesario para realizar tu instalación, ademas de componentes adicionales.

    Pirata Motor banner
    ( )
    MegaSquirtArgentina (B2Tech)
    Desde Buenos Aires, con representantes en todo el pais, somos los primeros distribuidores de Megasquirt para Argentina. Contamos con la mayor experiencia en el rubro ofreciendo la gama completa de productos originales de Bowling & Grippo, en unidades armadas o kits para ensamblar. Tambien distribuimos sistemas wideband en forma oficial, servicio de reparacion de ecus, instalacion y puesta a punto.
    ( )
    A dedicated tuning company specialising in the sales, installation and dynotuning of the MegaSquirt® System on all engines and types of vehicles We offer custom supercharger, turbocharger installations, fuel injectors, fuel pumps. and a range of Eaton M90 and M122 Superchargers You can rest assured your vehicle is in professional hands.
    ( )
    Distributeur Canadien des produits Megasquirt. Nos ECU assemblés sont munis de connecteurs commerciaux robustes permettant de supporter des courants plus élevés avec une plus grande robustesse. Our modified ECU can be adapted to your needs. We repair, modified and uprgade ECUs. We design extra boards or any needed circuit boards for applications.
    ( )
    FenixEcu est distributeur officiel de la gamme Megasquirt en France depuis 2008. FenixEcu vous accompagne de la définition du produit adapté à votre projet jusqu'à la mise en route de votre moteur.
    Reconnu par la profession pour le niveau d'excellence et la qualité de ses produits, FenixEcu vous propose tous les outils nécessaires pour l'automobile d'aujourd'hui et de demain.
    MegaSquirt Mexico
    De Chihuahua para México, somos distribuidores de productos megasquirt en toda la Republica Mexicana, proporcionamos un excelente servicio y asesoria en cada venta que realizamos, con nosotros adquieres confianza y seguridad en tu compra, contamos con un punto de venta adicional de kits de turbocargadores (intercoolers, blow off, wastegate, manifolds etc), widebands y otros productos.

    MegaSquirt Mexico on Facebook
    ( )

    Note that there are also a number of vendors selling MegaSquirt® in other venues, such as eBay. These vendors do not all have the same level of build quality, customer service, or commitment to the MegaSquirt® community as the distributors listed above. If you are not sure about a vendor, ask for customer feedback on, and check how active a vendor is on those forums as an indication of their level of support.

    Note that there are also a number of vendors selling MegaSquirt® EFI controllers in other venues, such as eBay. These vendors do not all have the same level of build quality, customer service, or commitment to the MegaSquirt® EFI controller community as the distributors listed above. If you are not sure about a vendor, ask for customer feedback on, and check how active a vendor is on those forums as an indication of their level of support.

    There is a listing of a number of additional MegaSquirt® EFI controller sellers on the forums at:

    Did I Buy a Counterfeit MS/MS2 Board?

    While not a new problem, reports of counterfeit MS/ MS2 boards have become increasingly frequent over the last year (2009), as have reports of poor design, workmanship, and above all, poor or non-existent tech support for these boards. And often they are not even cheaper than legitimate boards.

    If you are stuck with one of these boards, it may work for a while, it may fail intermittently, or permanently. It may never work. We cannot help you with troubleshooting these boards, since we do not know how they are designed or built.

    While we welcome innovation, there has to be some order to it or there is no longer a community. We encourage people to innovate new add-ons, new software, new applications for special purpose engines, etc. For this reason we have prototype areas and module versions of our boards, and we have GPIO boards that can handle all sorts of exotic and niche applications. And there is a wealth of very basic documentation on how anyone willing to learn can do this. People are free to innovate and sell these all they want. But that requires innovation and hard work - apparently it is easier to steal an existing design.

    People have asked us how they can tell if a board is counterfeit. There are three basic ways:

    1. Check the authorized dealers and resellers links above before you buy. These vendors are known to provide genuine B&G boards and provide good to excellent customer service.
    2. Because the list may not always be up to date, and because resellers may be very small entities, they may be legitimate, but not on the list. If they aren't, ask them which dealer they buy their raw boards from, then verify with the dealer. A legitimate vendor won't have a problem with this, in fact, it is a selling point to them.
    3. If you have already purchased a board, there are several ways you can check if the board is legitimate or not. This is particularly easy before assembly, but can also be done on fully assembled boards. For example, a red colored main board has never been produced by Bowling and Grippo. Other counterfeits are different in more subtle ways. If you are unsure, ask on the forums at for more details. We will provide detailed instructions here shortly.
    If your board is a counterfeit, ask the seller to replace it with a legitimate B&G version, or ask them to give you all of your money back.

    Note that V3 boards are less likely to be counterfeited than V2.2 boards (because they are more complex due to the many added features). However, counterfeits have been attempted of most of the B&G boards, unfortunately.

    It is strongly suggested that you purchase the following:

    1. A complete MegaSquirt® EFI controller kit,
    2. A complete MegaStim kit.

    You will have to decide if you want a MegaSquirt-I™ controller or a MegaSquirt-II. There's lots more information to help you make that choice here:

    The V3 main board is the latest version, and in most cases this is what you should use. It has a number of features that make upgrades and installations easier. See this link for more information about the V3 main board.

    An optional unit that eases installation (especially on previously carbureted engines) is the relay board.

    Bruce and Al do not support individuals who produce or sell their own version of the PCB. Bruce and Al cannot assure the quality control for any such boards, and every issue become prefaced with “what PCB are you using...” Having a sole source for the PCB is important because it is very time consuming to troubleshoot problems arising from other PCB designs or production methods. With the current system, the quality of the boards is assured and the people on the MegaSquirt Forums can answer questions relating to them. Users are not allowed to produce their own version of the PCB without express written permission from Bruce Bowling and Al Grippo. In general, such permission is granted only for one or two personal boards which will note be distributed in any form. Also note that such boards are NOT supported in any form on the MegaSquirt® EFI controller forums.

    About this Manual

    This manual has been produced for people new to the MegaSquirt® EFI controller to assist them to assemble, install and tune the MegaSquirt® EFI controller from the B&G partial kit and the specified Digi-Key parts. Unless noted otherwise, it is always assumed that:

    However, many MegaSquirt® EFI controllers have been installed on vehicles that do not conform to the above criteria. Many MegaSquirt® EFI controllers have been built in countries other than the U.S., and they have been installed on rotary engines as well. If your engine does not conform to the above list, read this manual first, and then check the MegaSquirt® EFI controller forums for information specific to other configurations and locations.

    This manual follows a sequence of tasks you need to follow to get MegaSquirt® working for you. However, it will not tell you absolutely everything you must do. This is not a step-by-step guide to everything you need to accomplish to install your MegaSquirt® (apart from the assembly guide for the unit itself). You will have to think some things through for yourself. This manual assumes you have some basic automotive, computer, and electronics background, or are willing to find, understand, and apply this information yourself. If you do not have such knowledge, you MUST consult a qualified mechanic. Otherwise you might be unlikely to successfully assemble, test, install, and tune the MegaSquirt® EFI controller. It is an experimental fuel injection unit, after all.

    One of the reasons the MegaSquirt® EFI controller came about was because Bruce and Al wanted to increase understanding of fuel control requirements for as many people as possible. In order to help the process of gathering knowledge, you need to understand your system thoroughly; something a step-by-step guide for everything is not conducive to. If you require a 'turn key' EFI solution, one of the commercial controllers might suit your needs better.

    A great many advanced topics have been left out of this manual, including: the hi-resolution code, the many useful variations of the standard code and hardware, running propane injection, etc. For information on these and other topics, see the FAQ and the msefi forums.

    Please report any errors, omissions, or clarifications to the MegaSquirt® EFI controller Forums, so everyone will be notified.

    Some Conversion Factors


    x 25.4

    = millimeters

    x 0.0394

    = inches


    x 0.306

    = meters

    x 3.281

    = feet


    x 1.609

    = kilometers

    x 0.621

    = miles

    cubic inches

    x 16.378

    = cubic centimeters

    x 0.061

    = cubic inches

    US gallons

    x 3.785

    = litres

    x 0.264

    = US gallons


    x 0.454

    = kilograms

    x 2.205

    = pounds

    pounds per square inch (psi)

    x 6.895

    = kiloPascals

    x 0.145

    = psi

    pounds per square inch (psi)

    x 0.068

    = atmospheres

    x 14.696

    = psi


    x 745.7

    = Watts

    x 0.0013

    = horsepower

    miles per hour (mph)

    x 1.609

    = kilometers per hour

    x 0.0621

    = mph

    degrees Fahrenheit (°F) = (degrees Celsius x 1.8) + 32
    degrees Celsius = (degrees Fahrenheit - 32) x 0.56

    miles per US gallon = 235/(litres/100km)
    litres/100km = 235/(miles per US gallon)

    MegaSquirt® and MicroSquirt® controllers are experimental devices intended for educational purposes.
    MegaSquirt® and MicroSquirt® controllers are not for sale or use on pollution controlled vehicles. Check the laws that apply in your locality to determine if using a MegaSquirt® or MicroSquirt® controller is legal for your application.
    ©2004, 2010 Bruce Bowling and Al Grippo. All rights reserved. MegaSquirt® and MicroSquirt® are registered trademarks. This document is solely for the support of MegaSquirt® boards from Bowling and Grippo.