Understanding MS

Understanding the MegaSquirt Engine Management System and choosing a system that is right for you:

What the heck is a MegaSquirt?

The MegaSquirt line of Engine Management Systems are Do It Yourself (DIY) systems capable of full standalone engine management at a fraction of the cost of the what the ‘big dogs’ charge.  They were designed with education and performance in mind, so that the do it yourselfer could learn the in’s and out’s of engine management and tuning, while learning a good bit about electronics in the process if you choose to build the unit yourself.  What you end up with is an incredibly performing EMS that you built yourself for ultimate bragging rights when you leave your buddies behind as a speck in your rearview mirror.  And you did this for a quarter to a tenth of the cost of a ‘big name’ retail standalone ECU. 

Building and installing a MegaSquirt EMS will require that you do some homework.  Some of the questions and answers below will help to guide you on where to start this and how to go about it.  You will learn a lot in the process and if you so choose you will come out of it with the knowledge to properly tune your car for the current configuration you have now, and for any future power combo you can dream up and implement.  There is no limit to what you can do or to how much power you can make with this engine management system.  We know right now of a MS user running low 10’s (10.08) in a 5000lb 4×4 truck making over 1000hp and 1000lbs/torque to the wheels (turbo/nitrous) who took first place in his class at Hot Rod’s Drag Week 2005 and 2006. he won a high dollar ($2400+) big-name EMS system in the 2005 contest, he quickly traded it away to stick with his trusty ole’ MegaSquirt 1, which he has a total of around $200 invested in.  We’ve got another customer making about the same level of power now on one of these units on a Land Speed car he runs out at Bonneville.  Again with an MS1 running the MS1/Extra firmware, he holds a world record in his class at 240 mph.  (Check out Gary Hart’s car out at this link).  Another customer we’ve been in contact with recently has a MegaSquirt 2 in his rear-engine dragster.  He’s running consistent 8.8 ET’s in the 1/4. 

This MegaSquirt thing is no joke.

Where do I start?

Read.  Then read some more.  If you skip this step you will be asking questions later that you could already know the answers to. We’re always glad to help though as this is a DIY based system some of the burden does fall on the user to do their homework, the big dogs charge an extra $2000+ for their systems to do some of the homework for you.  We’ll help you with your homework for free, but you’ve got to come up with the final answer.

Start with our “Which EFI system is right for me?” link on our site here: Which EFI system is right for me?

Then read applicable sections on your ECU choice at www.msextra.com

Then read about what is known as the MS/Extra firmware.  This is a free firmware update for the MS1 and MS2 that greatly expands the featureset of the ECU, highly recommended.

MS1/Extra Features and Documentation

MS2/Extra Features and Documentation  (includes MS2/Extra for MicroSquirt/MicroSquirt Module, and DIYPNP usage)

MS3 Features and Documentation – (All MS3 ECUs use a single firmware branch, and it’s written by the ‘Extra’ developers.)


Now that you’ve read up on things start lurking around and/or asking any remaining questions on the MegaSquirt Support Forums at www.msextra.com (Extra forums, advanced topics) and www.msefi.com (basic assembly guidance and support), there is so much helpful information at these two forums that it’s insane.  The search feature is your friend.  Try searching for your vehicle or engine, ‘RX7’, or ‘Subaru’, or ‘4AGE’ and then go through the threads that are returned.  There are a ton of very helpful people on these forums that will bend over backwards to make sure your project is successful, IF they can tell you’ve ‘done your homework’ and that you’re not expecting them to do all of it for you.  Questions like, “My car has an optical crank sensor in the distributor with one hole for each cylinder, spaced evenly apart.  Will the MegaSquirt-II work with this signal?” will usually get very quick and helpful responses.  On the other hand, questions like “What do I need to MegaSquirt my 1967 ‘insert make/model here?'” generally get ignored because it’s obvious the person didn’t put much effort into helping themselves.

Another link you might find interested–  http://www.msruns.com – This site allows users like yourself to proclaim their MegaSquirt’d success to the world, often with details on exactly how they implemented the system.  It’s organized by vehicle manufacturer so it’s easy to find others with similar vehicles to your own.

If you don’t know the right questions to ask, keep reading.  You’ll get it.

You can also Contact Us and we’ll do our best to assist you.  We have FIVE full time tech support gents on the team known for their knowledge base and response times. Please see this list of questions and help us help you.  The more prepared you are and the more you know about your car and your ignition system the faster we’ll be able to get you up and running!

What do I need?

Another question that doesn’t have a quick short answer… but the quick short answer is:  An ECU (there are a few options here of course), a stimulator (95% required), and a tuning cable.  Optionally you may need a USB-Serial Converter if your laptop doesn’t have a DB9 serial port, and/or a Wideband O2 system such as the Innovate LC-1 or LM-2 (with or without a dash mount gauge) which will make tuning your Air/Fuel Ratio SO much easier and more accurate that you’ll be glad you spent the couple of bills to do it.

Click Here to see a page we put together to assist people in these decisions— It doesn’t cover all of our products but it does cover some of the more commonly requested options at a high level and provides some idea of pricing (check our catalog for exact prices of each component).  For a complete product list, to validate current pricing and/or to place an order go to http://www.diyautotune.com/catalog.

How difficult is it to assemble a MegaSquirt myself?

It takes most people new to electronics assembly 6-10 hours for their first time assembly of a PCBv3 ECU, a bit less for a PCB2.2, and the stimulator (which you should do first) is very simple and takes maybe an hour to assemble for a first-timer.  Check out Youtube for some good solder technique videos like this one. We do often recommend you build your own MegaSquirt at least the first time around as it will familiarize you with the hardware particularly if mods are going to be required for your implementation.  This way it’s not all new to you when you get to the mods needed for your setup.

If you can follow step-by-step instructions, or paint by numbers, YOU can build a MegaSquirt!

Note we also offer all of our systems fully assembled if you’d prefer to skip the assembly phase.

I have a (insert year, make and model here), what exactly do I need to order for my car?

We’ll be glad to help you spec a system for your car but we’ll first need some basic information.  The following list of questions will generally need answers to in order to assist with this.  You can find this information in service manuals for your car/engine, on message boards and enthusiast sites, or sometimes by tearing into your ride and looking.  It will be a big help if you’ve followed the steps in the ‘Where do I start?’ section above so that you have a pretty thorough understanding of the MegaSquirt line of Engine Management Systems.  You may find that you’ve answered your own questions by the time you’ve done this. 

(Please try and answer all questions as the two most often skipped (3&4) are the most important for ignition control!)

  1. What year/make/model/engine/tranny? (Pretend your at the parts store, ordering a starter.)  If this isn’t the original engine/electronics let us know that too.
  2. Are you looking to control fuel only, ignition only, or fuel and ignition? Is there anything beyond these features that you are looking to control – fans or boost, for example?
  3. Is it important to run sequential injection for this project, or is bank to bank fueling OK? (See our notes on sequential injection if you’re not sure.)
  4. What are the engine details (type, number of cylinders, previously fuel injected or carb’d?)
  5. What type of ignition system does your car run? Is there a distributor?  Coil pack?  Coil on Plug?
  6. What sort of sensor(s) does it use to trigger the ignition? Variable reluctor (magnetic pickup)? Optical? Hall effect? Old fashioned mechanical breaker points? Are the sensors triggered by trigger wheels on the crankshaft / flywheel, distributor / cam, or both?
  7. How many teeth / windows / slots and are on the crank or distributor trigger wheel? How are they arranged? (Equally spaced, missing teeth gaps, etc)
  8. Does this engine have a fast idle valve (IAC)? If so, how many wires are connected to it?
  9. Rate yourself 1-5 on technical confidence in yourself.  1 being “I can’t paint by numbers” and 5 being “I can probably build a car from scratch if I have the right documentation, and I’m resourceful enough to do some research and find some of my own answers.”  We need to know this as some of the ‘less traveled’ roads will require you to make modifications that in some cases we haven’t performed ourselves yet and based on this response it will help us to know whether this type of solution is for you or not.  I challenge you to ‘stretch yourself’ a little bit.  You won’t ever learn anything (about yourself and your abilities) if you don’t try to do things that you’re not quite sure you can do… and then find that you can.
  10. Are you looking to build your own ECU from a kit or buy a pre-assembled ECU?
  11. Are you open to retrofitting a different ignition system such as the Ford EDIS distributorless system or one of our crank trigger kits if it is determined that the MegaSquirt will not properly (or easily) control your factory ignition system?  Many factory systems MegaSquirt can simply take control of, some it cannot.  EDIS to the rescue!  It’s cheap, simple and works great!

If you can cut and paste the above list into an email and answer all questions it would be very helpful to us– otherwise we’ll likely have to ask you the same questions in order to best assist you.

Also– Here is a page we maintain with links to installation documentation for various different vehicles that we’ve found around the web— Even if it’s not an exact match there is much to learn by looking over other’s installations and notes. 

If you find or write more install docs that we can add here please let us know.

What is the difference between the MegaSquirt PCB 2.2 / PCB 3.0 / PCB 3.57?

They are all three able to use the MegaSquirt-I CPU as well as the MegaSquirt-II and MegaSquirt-III daughterboards, but they are based on different versions of the circuit board and as such there are different features .  You can click on any of the headings below to view an example of the product with pictures.


The v2.2 board dates back several years, it’s the least expensive of the currently available options, and the least developed.  It’s a great low budget solution that has served many people well (and continues to).



The v3.0 board has a lot of improvements made to it to reduce electrical noise and increase robustness (damage resistant), as well as make the board easier to expand.  All of the improvements with the V3.0 board are listed here.

The main high level differences are that the uprated flyback circuitry is included so you can run low or high impedance injectors, there are several improvements to make the board more robust and harder to damage in the event of a mis-wire or overload event. A prototyping area was adding to the PCB, and several changes were made to prepare the board for the MegaSquirt-II and MegaSquirt-III Daughterboards.



The v3.57 board’s major claim to fame is it’s ‘surface mount (SMT)’ design.   Otherwise it is almost identical to the v3.0 board and the above information on the v3.0 board fully applies.  The only other major differences are:

A) the addition of a PWM capable idle control transistor allowing control of a PWM idle valve or a standard on/off type FIDLE valve without need for modification.  This was a common modification applied to the v3.0 board and is no longer needed on the v3.57.

B) the addition of a DB15 connector next to the DB9.  By default this doesn’t do anything, but is there to allow for extra I/O for modifications.  It takes the place of the externally viewable LEDs, which are now internally surface mounted on the PCB.

C) Several signal pads have been added making common modifications easier.

D) The prototype area was sacrificed (removed) to make all of the above possible.


In general, if you’re looking for the cheapest option possible, the PCBv2.2 makes sense.  Chances are you’ll mate an MS1 processor with it in this case, such as with our MegaSquirt-I kits and assembled units.  Otherwise, if the small difference in price is worth it to you to go with a tougher and more featured board that was built with expansion in mind, the v3.0 or v3.57 boards make more sense.  We offer MegaSquirt I’s, II’s, and III’s using these two boards.  Some prefer the thru hole v3.0, and some prefer the v3.57.  See the above to decide your preference between the two.

How big is the MegaSquirt case?

The MS1 and MS2 cases are is 6.2″ x 4″ x 1.75″ with mounting flanges on each end that are about .5″ long, so total length including flanges is about 7.2″.

The MS3 cases are a little taller, about 6.2″ x 4″ x 2.6″, again with mounting flanges on each end that are about .5″ long, so total length including flanges is about 7.2″.