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.product disclaimer


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.

product disclaimer

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/transmission? (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? 
  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. Beyond fuel and ignition, are there any other must-have features, such as internal SD card data logging instead of logging to a laptop, boost control, nitrous control, cooling fans, etc?
  5. What are the engine details (type, number of cylinders, previously fuel injected or carb’d?)
  6. What type of ignition system does your car run? Is there a distributor?  Coil pack?  Coil on Plug?
  7. 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?
  8. How many teeth / windows / slots and are on the crank or distributor trigger wheel? How are they arranged? (Equally spaced, missing teeth gaps, etc)
  9. Does this engine have a fast idle valve (IAC)? If so, how many wires are connected to it?
  10. 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.
  11. Are you looking to build your own ECU from a kit or buy a pre-assembled ECU?
  12. Are you open to retrofitting a different ignition 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, or if we determine your existing sensors / ignition do not support the features you would like to add to this motor?

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.

product disclaimer

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″.

MegaSquirt Tech:

Quick Tech Tip: MS3Pro, MSPNP, MegaSquirt and Windows XP

Products this applies to:

MS3Pro, MSPNP, MicroSquirt, MegaSquirt 1/2/3 with TunerStudio on a Windows XP PC



If you’re trying to connect to any of our MegaSquirt based products with Windows XP and you’re having trouble — here’s the skinny:

The serial library was updated to support Mac OS M1 and ARM64 on Linux.. Unfortunately, it seems they have stopped supporting the 21 year old Windows XP which has impacted TunerStudio on Windows XP…..

Short Term Solution:

You will need to let it overwrite the file that is there.

Thanks to Phil Tobin @ EFI Analytics for this!

Long Term Solution:

  • This is resolved in the latest TunerStudio beta version and beyond. The resolution is that on start up, if TunerStudio detects that it is running on Windows XP and using the 2.9.4 JSSC library, TS will replace the library with the 2.8 version that it used to use.

How do I power cycle or reboot a MegaSquirt?

Power cycling and rebooting simply mean turning the MegaSquirt off and back on again. Some settings only take effect when the MegaSquirt powers up. The latest versions of MS2/Extra and MS3 firmware will display a message in TunerStudio when you change a setting that requires power cycling to take effect.

Can I use the stock IAT and CLT sensors with the MegaSquirt?

Yes you can in almost every case– the exception is that you sometimes remove your stock IAT sensor when you remove your MAF/AFM as it’s often built into stock MAF or AFM on many cars.  If this is the case, you’ll need to add another IAT sensor to the intake tube, usually just before the throttle body and after the intercooler, if you have one.  The idea is to measure the air temp as it enters the engine.  After anything heats it up (like a turbo/supercharger) and AFTER anything cools it down (intercooler, meth injection, etc).  You want the actual air temp of the air as it enters the engine.

Here’s an article that shows how to measure the resistance curve of your stock (or any really) sensors so that you can input these values into your MegaSquirt EMS via the tuning software for MS2/MS3 ECUs, or via EasyTherm for the MS-I, to calibrate your ECU for your sensors.

Tech Article:  Measuring and Calibrating your Coolant (CLT) and Intake Air Temp (IAT) sensors

product disclaimer

Using the Relay Board with the PCBv3, what do terminals S1-S5 do?

You can use the schematics for the PCBv3 ECU and/or PCBv3.57 and the Relay board to trace it back. Here are the Relay Board schematics and here are the PCBv3 schematics and PCB v3.57 schematics.

Here’s the quick answer though mapping these terminals back to the corresponding pin on the PCBv3 ECU’s DB37:

S1 = 25
S2 = 27
S3 = 29
S4 = 31
S5 = 36

With the MS-I these were unused by default, available as spare inputs/outputs. With the MS-II and MS-III (legacy installation) S1-S4 are used for the stepper motor IAC, and S5 is the ignition output.

For more information on the Relay Board check out this page:  http://www.bgsoflex.com/mspower/mspower.html

Note you can do the same cross reference for the PCB2.2 ECU and the Relay Board, just use the PCB2.2 Schematics.  Though the pinout is of course the same…

I’m considering an EFI conversion – converting my car from carbs to EFI – what do I need to consider?


Your fuel system will need to be converted to a high pressure system suitable for fuel injection (around 43.5 psi for MPI, less for TBI if you go that route).  If you can get a TBI unit (with TPS) that bolts to your manifold, that may be the simplest route (though their likely will be more power and better economy/emissions in a good MPI setup), otherwise you’ll need to buy or fab up an intake manifold and throttle body with TPS, fuel rails, etc.    We don’t carry intake manifolds at this time, though we do carry many of the fuel system components you will need, and of course the engine management systems and accessories.

FOR FUEL AND IGNITION CONTROL– We’d suggest running a MegaSquirt-II, or MegaSquirt-III, using the PCB v3 or v3.57.  You’ll need a compatible Crank Angle Sensor to determine engine position and RPM from as well as some way to fire the ignition — with the MS2 this is generally a distributor based solution or the Ford EDIS or GM DIS distributorless solutions which could be adapted to your engine (most adaptations use EDIS which also uses it’s own 36-1 Crank Angle wheel which can be mounted on the crank pulley).  You can read more about ignition options in the MS/Extra documentation at http://msextra.com/doc/index.html.

FOR FUEL ONLY– You could run any of the MegaSquirt ECUs, the MS1, MS2, or the MS3.  We’d recommend PCB v3.0 or PCB v3.57.  Pickup up your ignition signal from the negative terminal of the coil, run your IAT, CLT, TPS, and O2 sensor inputs to the MegaSquirt, calibrate the MS to the sensors if they are not GM sensors and start tuning.

If you haven’t yet we’d again suggest taking a look through the MS/Extra version of the manuals at http://msextra.com/doc/index.html as it will go into detail about most aspects of the conversion/installation/configuration/tuning and help to make things clearer.

Here’s a list of what most people would commonly pick up:  We’ll list what we see as ‘required’ and then some ‘recommmended’ and ‘optional’ components.  Then we’ll provide a link that goes into some detail on why we made these recommendations and that will also help you to decide on the optional components.


(Note you can substitute DIY kits for the below to save some cash and learn more about your EFI system, and electronics in general, in the process.)


along with:

‘Highly Recommended’

Innovate LC-2 Digital Wideband Controller with Sensor

12′ MegaSquirt Wiring Harness (MS1 / MS2 Ready)  and possibly the MS3X Harness as well if you’re running the MS3X board.


MegaSquirt Relay Board – Assembled Unit

MegaSquirt-I Relay Cable (if you’re using the relay board and cable, you don’t need the standard MSHarness12, see note in product description)

GM Open Element IAT Sensor with Pigtail

GM Closed Element CLT / IAT Sensor with Pigtail

USB to Serial Adapter


Here’s the link mentioned above with more info on each —

What do I need?

product disclaimer

Idle Air Control Valves vs. Fast Idle Valves— What does my car have and how can I tell?

Here’s a way to figure it out–

On a cold morning, when you start your car up on a stock Engine Control Unit, it idles higher than normal right?  That’s because this valve is partially open letting more air in to idle the car up so that it warms up faster.  Now… if you sit there until it warms up, does the idle drop back down to normal all of a sudden?  If so it’s a Fast Idle valve (generally two wires, ground and 12v+).

Alternately, does it slowly idle back down to normal a little at a time, gradually reducing the idle speed as the engine warms up?  If so it’s either a PWM valve or stepper motor valve.

To determine if it’s a stepper or PWM valve, find the valve on your engine, it will be attached to the intake manifold, either directly or via a hose.  How many wires does it have?  Generally a PWM valve will have 2 wires, sometimes 3, and a stepper motor IAC will have 4 wires, sometimes 6.  The MS2/MS3 stepper circuit was designed with GM/Jeep valves in mind, however it works great on many different stepper IAC systems, including most all USDM, Euro, and Japanese vehicles that use steppers, among others.

Browse our idle air control valve and control components here.

Is there a central place where I can download maps that others have shared?

Maps can sometimes be found on the http://www.msextra.com or http://www.msefi.com forums that are similar enough to be used as a base map for your vehicle but it’s generally not encouraged to just grab someone’s map and run with it, as there are a few things to consider first. You want to ensure their setup is as similar to yours as possible, including the engine, ignition system, MegaSquirt version and firmware version they’re running.  If they were running a different MS version, or firmware version than you then you can still copy the information from their map manually, but don’t import it into your ECU as it’s very possible some of the data won’t import properly into a different firmware version.  This could help you get started in the right direction towards building your map.

Another important question to consider, especially if the ECU setup you’re using required mods to control your vehicle’s ignition system, is are the mods you’re using identical to the mods used by the person that created the map?  Are they using the same ignition components (ignitors, coils, etc)?  If anything is different here their ignition settings could be different from what you need, and could damage your coil or ignitor.  Things to watch out for are the SPARK OUTPUT setting (inverted or non) and the DWELL settings. 

The most important thing to remember is that no matter how good so-and-so told you their map would work on your car, you are still ultimately responsible for making sure your ECU is properly setup for your car, and that your car is properly tuned.  That means looking over the map’s settings BEFORE you start the car.  Do the ignition settings look right and does the ignition table look logical?  Is there 60 degrees of timing at WOT?  If so, that’s probably not right….  When you start the car you should still treat it like you need to tune it yourself from scratch, however you hopefully have a good head start.  Tune the idle first, then slow speed VE and ignition, cruise VE and ignition, and then work on up to higher loads and finally WOT VE and ignition.  Spend some significant time on http://www.msextra.com/   Another great resource is Matt Cramer & Jerry Hoffmann’s Performance Fuel Injection Systems.

product disclaimer


Wanna learn more about how to tune EFI and Electronic Ignition?  OF COURSE YOU DO!
EFI Tuners Guide Banner with Carl in Camaro on laptopCheck out the EFI Tuners Guide!  How to Install, Configure, and Tune EFI!

The MegaSquirt 1 and 2 ECUs seem to have only four injector output pins (or terminals on the relay board) but they are labeled as pairs so this is even more confusing, do I have two or four injector outputs? And how does either two or four outputs allow me to run 6, 8, or 12 injectors?

With the MS1 and MS2 you have two ‘banks’ or groups of injectors.  You can use one or both of them. With 1-6 cylinders one is fine, though you can use both and generally would do so unless you were using the second bank for a different purpose, such as staged injection. With more than six you should share the load across both banks. 

Each bank has two terminals that you bring together to a nice fat (i.e. 14ga) wire that goes out to all of the injectors on that bank. For an 8cyl example you might choose to run two banks of 4 injectors each. You’ll run 12v to one side of all eight injectors that are hot in the ‘crank’ and ‘run’ positions. Similarly, you’ll run the 14ga wire out from one pair of terminals (one injector bank output) nearby the injectors where you’ll split that 14ga off into 4 smaller gauge (20ga likely) short wire runs to the individual injectors. Do the same thing for the other bank.

For sensor & wiring diagrams, please visit http://www.msextra.com/manuals/schematics/

Note that when running a MegaSquirt-III, you can still run batch injection if you choose, using the same wiring diagram as above.  However you can also purchase your MegaSquirt-III with the MS3X Expander Board, and then have up to 8 channels of sequential fuel and ignition outputs available.  (Not to mention all of the other features this enables, lots of I/O).

Check out the MS3X Wiring Diagram here.

Is the MegaSquirt Engine Management System just for making more power? Or can I get better gas mileage out of it too? What about emissions?

MegaSquirt Engine Management Systems are most often installed in the pursuit of power gains, but often economy gains are just as possible.  In fact, due to the nature of programmable fuel injection usually you can achieve some of both: power when you are on the throttle and economy when you are lightly cruising around town.  It’s really all in the tune.  The factory will have tuned your gasoline engine to run around at 14.7:1 air/fuel ratio (AFR).  This is the ‘chemically correct’ or ‘stoicheometric’ air/fuel ratio, which basically means this is the air/fuel mixture at which the most complete burn of the fuel will occur.  It is also the proper mixture for the catalytic converter to best do it’s job.  In other words, your car comes tuned from the factory for reduced emissions.  If your goal is power, you’ll be tuning a somewhat ‘richer’ mixture than this; for a naturally aspirated car this is usually in the 12.6:1-13:1 range under throttle.  For economy you’ll tune somewhat leaner than this.  As lean as 16:1 possibly if your engine runs well there, or maybe even a small amount leaner when lightly cruising on the highway.  That can lead to quite an improvement in highway mileage over the factory 14.7:1 tune.  Not all engines like to cruise this lean so your ‘mileage’ may vary.  Our MR2 seems to love 16:1 on the highway– We were able to get 34.5 MPG on an 1100 mile trip at an average speed of 70 MPH- a decent increase over stock for sure!  And one of the great things about EFI is you don’t have to sacrifice WOT power to do this– the MR2 that’s getting better mileage than stock on the highway also makes more power than stock when you step on it– it’s an entirely separate part of the EFI map!

If tuning for emissions is your goal, it actually may be possible to do a better job than the factory did, though your task will be tougher as that’s at the top of the factory’s priority list.  Areas you may be able to improve:  Often factory cars idle richer than 14.7:1, and under power are again richer than 14.7:1, though they likely need to be at wide-open throttle.  With proper tuning, there is likely room for improvement in emissions and fuel economy.

product disclaimer


Sequential Fuel Injection – Do I need sequential injection to make big power? Does MegaSquirt EFI offer Sequential Injection?

What is Sequential Fuel Injection?

Sequential fuel injection attempts to only spray fuel while the intake valve is open for the cylinder that is about to fire, which in most cases is only possible at low engine speeds between idle and low speed cruising.  Benefits can be seen in emissions, drivability, and fuel economy particularly at these low engine speeds and loads.

Batch Fuel Injection

Batch injection (which is what the MegaSquirt-I and and most MegaSquirt-II versions do) does not attempt to spray only when the valve is open.  It’s a fact that at higher engine speeds you won’t have enough time to spray all fuel while the valve is open, making this somewhat pointless, particularly for a performance oriented application.

At these higher engine speeds 99% of sequential systems (exceptions being race only systems with super massive injectors) cannot spray all of the fuel needed while the valve is open anyways, and sprays it both while the valve is opened and closed, very much like a batch system such as the MegaSquirt I and II.

Batch versus Sequential — what gives?

Read Chapter 4 in the EFI Tuners Guide for more information on the benefits of sequential versus batch fuel injection.  You might enjoy that entire series actually!

We’ve dyno tested several cars with using batch fire and sequential injection on the same motor. Peak power was more or less the same so long as we did not employ individual cylinder tuning on the sequential injection system. Worth noting though, the sequential fuel injection system did fire up a bit smoother/easier, and run a bit more smoothly at idle and at light throttle angles.  But for a race car, many would say you’re splitting hairs a bit there.  If you want to know where sequential fuel injection systems really shine in getting the MOST out of a motor, read on!

The MegaSquirt III system with the MS3X Expansion board or MS3-Pro will do full 8 cylinder sequential fuel and ignition.  If you’re looking for the absolute best possible emissions and fuel economy, as well as the ability to fine tune each cylinder individually, then the MS3 system is the way to go.

As for Plug-N-Play (MSPNP and MSPNP Pro) systems offered by AMPEFI/DIYAutoTune, the MSPNP Gen2 systems support sequential fuel injection for 4 cylinder vehicles so long as the stock ignition system offered up the crankshaft position sensor and camshaft position sensor signals needed for us to be able to do so.  MSPNP Pro systems offer the same support of sequential fuel injection for up to 8 cylinders (and more is possible if we were to build an MSPNP Pro for a vehicle with higher cylinder count, the core supports it).

As a general rule, most of the benefits of ‘going sequential’ are in the fuel economy and emissions space– there is generally no significant performance difference with a sequential system over a batch system unless you use individual cylinder tuning. There can be minor emissions and fuel economy benefits particularly at very low speeds though. If your tuning budget allows for individual cylinder tuning, it may be possible to pick up 3-4% more power depending on how much cylinder to cylinder variation your engine has, while also helping to ensure that you can tune your engine to be as safe as possible while still pushing it to the max.

So are there benefits to ‘going sequential’?  And are they worth it?

Well, in a word, YES!  Automakers would not have made this the standard years ago were there not.  That said, they mostly come into play regarding improved emissions and fuel economy, which is obviously a key focus of OE automakers.  For a pure race car as we tend to cater to, the answer is closer to…. it depends.  If you’re going to take full advantage and tune each individual cylinder like it was it’s own independent engine, and remove the variability of air/fuel ratio per cylinder that is native to ALL engines by dialing each cylinder in to it’s unique airflow characteristics– the by all means, yes!

With a properly setup and tuned sequential fuel injection system using good data and dialed in on a proper dyno, you will be able to make all of the power your engine can SAFELY make by tuning all the cylinders to your target air/fuel ratio, and pushing your ignition timing to the max that you can safely run, knowing now that your AFR is safe, and you won’t have one lean cylinder ruin your day!   On the other hand, if you’re going to slap that system on your engine and tune to a single O2 sensor in a combined tailpipe, you’re getting the average of all cylinders in a single reading, and you won’t know which cylinder is contributing most to the mix.  This will lead to a need to be just a touch conservative regarding ignition timing, and target air/fuel ratio.

So- give me an example of the difference!

Hypothetical – If you were perfectly tuned with all cylinders balanced for instance using a sequential injection system with individual cylinder tuning, let’s say you should be able to run 15 degrees of timing and 11.5:1 gasoline air/fuel ratio (AFR) under boost… you might instead run 13 degrees and 11:1, using a bit more fuel overall to help ensure that you don’t have a dangerously lean cylinder, and using a bit less ignition advance overall just in case you do!

MS3Pro and MSPNP Pro have you covered!

Check out the MS3Pro and MSPNP Pro systems (which are MS3Pro inside – aka MS3Pro PNP) and their capability to help you, along with the TunerStudio tuning software, to not only tune each cylinder out individually by hand/manually– but also to do so using VE Analyze Live, our version of ‘autotune’, to automatically tune each cylinder of your engine for you!

You can do this with individual wideband o2 sensors on all cylinders… OR… you can do this by moving a single wideband o2 sensor around and letting TunerStudio build a trim table for each cylinder one at a time!  We’ve been offering this feature with our sequential fuel injection systems for years now, we’re still waiting for the ‘big name marketing machine ECU made in who-knows-where manufacturers’ to catch up and try to claim they did it first.  As usual, they didn’t, we did!  And we made them, and continue to make them, right here in the USA!

AMPEFI Bald Eagle in front of a flag - Made in the USA

product disclaimer



Wanna learn more about how to tune EFI and Electronic Ignition?  OF COURSE YOU DO!
EFI Tuners Guide Banner with Carl in Camaro on laptopCheck out the EFI Tuners Guide!  How to Install, Configure, and Tune EFI!

How does a MegaSquirt compare to having my car ‘Chipped’?

It is possible to get many of the same performance benefits of the MegaSquirt by having your car chipped IF the tuner chipping your car has your car onsite and custom tunes the map for your specific configuration on a steady state/load bearing dyno.  If you are not the hands on type, or you don’t plan to EVER modify your car/engine again, then this is not a bad option.  If you do ever mod your car again it will likely need to be re-chipped, on a dyno by a qualified tuner, to get the maximum performance out of it.  If you simply send your ECU off to a chipping company who is supposed to load a map on your car, or buy a canned tune online to load on the chip yourself you’re likely not going to get the results you’re after.  In either case that tune/chip was NOT designed specifically for  your car on a dyno by a qualified tuner so you are simply not going to get the maximum performance possible out of the engine.  They simply can’t do it– they have to make a lot of assumptions with no scientific testing on YOUR car. 

However, if you really want to take control of things, if you do have plans to further modify your car and you don’t want to have to pay someone to rechip it every time you mod it, and if you are open to learning something in the process then by all means a standalone EMS is the way to go.  And there is no more powerful system per dollar spent than the MegaSquirt, in fact even with the affordable price out of the picture the MegaSquirt line of Engine Management Systems rival the featureset of many aftermarket ‘high dollar’ systems.  Particularly the MS3-Pro Stand Alone EMS.  We’re talking 100% of the functionality of many high-dollar systems, without the high-dollar price tag.

product disclaimer

How DIYAutoTune Configures it's Assembled MegaSquirt ECUs:

There are several ‘optional’ or ‘choice required’ steps during assembly of the PCBv3 MegaSquirt units, how are the DIYAutoTune ECU’s configured?

MegaSquirt-I EMS’s are setup by default as a fuel only EFI controller running though they are running the current stable release of the MS1/Extra firmware.  These are configured to be triggered from the (-) negative terminal of the coil by default.  It is fairly easy to convert them to be triggered from a Hall/Optical/Points trigger if you prefer.  Here are the steps to take:

  • Cut out C12 and C30.  Don’t jumper them or anything, just clip the leads and leave them out.  (Assembly steps 50h and 50d)
  • Jumper D1.  You can remove the diode first, but you don’t have to.  It’s easier to just solder a little lead shorting both of it’s legs together.

MegaSquirt-II EMS’s are by default configured for fuel and ignition control running the current stable release of the MS2/Extra firmware.  These are configured to be triggered from a Hall/Optical/Points trigger by default. 

MegaSquirt-III EMS’s are by default configured for fuel and ignition control running the current stable release of the MS3 firmware.  These are configured to be triggered from a Hall/Optical/Points crank trigger by default, and with the MS3X board added also support a similar Cam sensor input allowing sequential fuel injection. 

WideBand o2 / Oxygen Sensor Systems from Innovate Motorsports:

How do I configure TunerStudio for the Innovate LC series, MTX-L, or LM-1 / LM-2?

For a long time we guided customers on how to re-program their LC-1 / LM-1 / LM-2 to output a slightly different signal from default.  The goal of this was to increase the resolution of the signal in the range of AFR most users will spend their time in.  We used to recommend programming the output you were using to send a signal that represented a 10-20:1 AFR from 0-5v.  While in theory this is great and does increase resolution a bit, in practice it’s not really needed and is probably more trouble than it’s worth for most users.  We now recommend leaving the analog outputs on your LC-1 / LM-1 / LM-2 at their default settings (which is 0v = 7.35:1 AFR, and 5v=22.39 AFR).  Proceed to configure the TunerStudio tuning software to allow your MegaSquirt EMS to properly talk to your LC-1 / LM-1 / LM-2 do the following:


With your TunerStudio project open, go to:
File > Project > Project Properties and click on the Settings tab
Under EGO O2 sensor, chose the right option (Innovate LC-1 Default) for your wideband in the drop down menu and click Ok.  TunerStudio will quickly restart and take you back to the main dashboard.

Next, click on the Basic Settings tab and chose Exhaust Gas Settings.  You will need to change your EGO Sensor Type to wideband.  Burn the change to your MegaSquirt.

Your AFR Targets Table will open underneath the More Settings tab.


With your TunerStudio project open, go to:
File > Project > Project Properties and click on the Settings tab
Under EGO O2 Sensor, chose the right option (Innovate LC-1 Default) for your wideband in the drop down menu and click Ok.  TunerStudio will quickly restart and take you back to the main dashboard.

Next, click on the Basic Settings tab and chose EGO Controls.  You will need to change your EGO Sensor Type to wideband or dual wideband as appropriate for your setup.  Don’t forget to burn the change to your MegaSquirt. Lastly you will need to go to the Tools menu up top and click on Calibrate AFR Table.  Chose your sensor type (Innovate LC-1 Default) in the drop down menu, and click on Write to Controller.  This is a one way flash, so don’t be alarmed if your settings don’t ‘stick’ in this menu after you’ve sent them to the controller.  After the write is complete, click Close.

Your AFR Targets Table will be under Basic setup > AFR Table 1


With your TunerStudio project open, go to:
File > Project > Project Properties and click on the Settings tab
Under EGO O2 Sensor, chose the right option (Innovate LC-1 Default) for your wideband in the drop down menu and click Ok.  TunerStudio will quickly restart and take you back to the main dashboard.

Next, click on the Fuel settings tab and chose AFR/EGO Controls.  You will need to change your EGO Sensor Type to wideband.  Most setups will use a single sensor with the input received on DB37 Pin 23.  If this is the case for your application, enter 1 for Number of sensors and set your EGO Channel to Normal EGO.  This is a pink wire labeled “O2” on our harness.  If you are running multiple widebands, you will be able to set that up in this menu as well.  Don’t forget to burn the change to your MegaSquirt when finished.

Lastly you will need to go to the Tools menu up top and click on Calibrate AFR Table.  If  the option for Calibrate AFR Table is grayed out, you will fist need to go to Tools > Un/Lock Sensor Calibrations, choose Unlocked, and Burn and Close.  Then you will be able to access the Calibrate AFR Table menu under Tools.  Choose your sensor type in the drop down menu (Innovate LC-1 Default), and click on Write to Controller.  This is a one way flash, so don’t be alarmed if your settings don’t ‘stick’ in this menu to be later viewed again after you’ve sent them to the controller.  After the write is complete, click Close.  If you desire, you can lock your sensor calibrations again by visiting the Tools > Un/Lock Sensor Calibrations menu again.

Your AFR Targets Table will be under Fuel settings > AFR Table 1

How should I wire up my Innovate LM-1 or LM-2?

Begin by following the ‘Quick Start Guide’ that comes with the LM-1 / LM-2.  

In addition, DIYAutoTune recommends:

  • If you are simply using the LCD display on the LM-1 / LM-2 to tune your car you have nothing different to do.  However, if you are routing an analog output from the LM-1 / LM-2  into the MegaSquirt you should ground the LM-1 / LM-2 and the MegaSquirt at the same point.  This is to prevent a voltage differential and will ensure accurate readings.  You might even clip the cig lighter connector wire that comes with the LM-1 / LM-2 and put quick disconnects on it, and install the same type of quick disconnect connectors on the MS Harness so I can pull power and ground from the same source it pulls from, ensuring the MegaSquirt gets an accurate sensor reading. 

Note– You do not ever need the 470 ohm resistor with the LM-1 or LM-2.

How should I wire up my Innovate LC-1 or MTX-L?

Begin by following the ‘Quick Start Guide’ that comes with the controller.  If you lost that or need a copy of it for some reason you can download it here:  LC-1 Quick Start Guide for the LC-1, LC-1/XD-1 Standalone Gauge Kit  if you have the combo kit, or MTX-L Manual for the MTX-L.

In addition, DIYAutoTune recommends:

  • Grounding the controller and the MegaSquirt together.  This is to prevent a voltage differential and will ensure accurate readings.
  • The factory EFI system’s fuel pump relay often makes a good source for 12v switched power.  This is a required source for 12v, but often a good one…
  • For the LC-1, wire the brown (analog out 2) wire to the MegaSquirt’s O2 input wire. For the MTX-L and LC-2, the default analog outputs are reversed, so you’d wire the yellow (analog out 1) wire to the MegaSquirt’s O2 input wire.

For any LC-1 purchased after June2006, that should be all you need to be concerned with when wiring it up.


IF YOU PURCHASED YOUR LC-1 PRIOR TO JULY, 2006: Use a 470 ohm, 1/4watt resistor in between the analog output of the LC-1, and the o2 input of the MegaSquirt.  So you’ll wire the analog output from the LC-1 to one side of the resistor, and then you’ll wire the MegaSquirt 02 input to the other side of the resistor, forcing the signal to pass through it.

Do I have the newer or older style LC-1? Should I get it replaced if it’s older?

You can skip this section if you bought your LC-1 after June of 2006.

First…  If there is a voltage differential or any other cause that would pull your 5v output to anything above 5v it could burn out the DAC on the older model LC-1.  Wired properly most people never had a problem with them but Innovate proactively made the circuit more robust, replaced faulty units and provided an updated version of the product.  Their handling of this issue was truly a class act.

The ‘older model’ LC-1’s were up until about June 2006, in white/beige box.  The new models were sold since then and Innovate updated the packaging at about the same time to a blue/black box and later still to a white/red box.  The more definitive way is to determine which model you have is to check the serial number.  The serial for the LC-1s with the analog output fix are LC11188 forward and all LC-1s that start with CLC.  Note that in  fall 2007 Innovate started using a white/red box, these are still the new LC-1’s, just using a different box design.

Bottom Line: Wiring it according to the docs is the most important thing. Not just for longevity but for accuracy as well. You don’t want a voltage differential in your readings so you definitely want to ground your LC-1 at the same point as your ECU (assuming you’re feeding the output back into the ECU) or datalogger if that’s what you’re using. Then ground the heater ground to a separate point as per the docs. This will make even the old LC-1’s last forever in our experience.

Is a wideband o2 sensor better for tuning AFR than a narrowband o2 sensor? Isn’t my 1/2/3/4/5 wire stock o2 sensor good enough?

Wideband o2 sensor versus narrowband o2 – what’s the difference?


A wideband o2 sensor system will give you far greater tuning ability than a narrowband o2 sensor.  The challenge with a narrowband sensor is that it is only truly accurate at 14.7:1 AFR (the stoichiometric air/fuel ratio for gasoline).  The factory will most likely have tuned your engine to run around at 14.7:1 air/fuel ratio (AFR) at cruise and light load conditions. This is the ‘chemically correct’ or ‘stoichiometric’ (stoich for short) AFR which basically means this is the air/fuel mixture at which the most complete burn of the fuel will occur. It happens to also be the proper mixture for the catalytic converter to best do it’s job.  In other words, your car comes tuned from the factory for reduced emissions and that’s why that narrowband sensor is there.

Therefore a narrowband will be useful for tuning cruise Air/Fuel Ratio (AFR) only as long as you’re tuning for 14.7:1 air/fuel ratio.  However, under Wide Open Throttle (WOT) you’ll want to tune for somewhere between 12.6:1 and 13:1 on a naturally aspirated motor, or richer for forced induction, and the narrowband won’t tell you anything useful at that range beyond ‘you are richer than 14.7:1 but I don’t know by how much’.  Likewise at cruise you may not want to tune for 14.7:1, maybe you want to ‘lean burn’ chasing better fuel economy at cruise and you want to tune to 15.5:1 or even a bit leaner possibly.  That narrowband sensor can again only tell you ‘you are leaner than 14.7:1 but I don’t know by how much’. Only a wideband o2 sensor and controller can give you accurate feedback outside of the stoichiometric 14.7:1 reading that NB sensors are designed for, and allow you to tune for best power and best economy.

You need solid data to tune your engine right.

In short, a wideband oxygen sensor will give you a measurement of your Air/Fuel Ratio from about 10:1 up to about 20:1 AFR allowing you to target exactly the AFR you’re after at all times.  If you’re running a naturally aspirated car on a road racing course, you might target 12.5:1 – 13:1 range under heavy load/throttle.  If you’re running a turbocharged land speed car down the Bonneville Salt Flats, you might target 11:1, or possibly richer.  A wideband o2 sensor gives you the data you and your ECU need to be able to tune that properly.  While a narrowband can only tell you when it’s 14.7:1, and is therefore nearly useless for tuning for anything other than a steady cruise condition.

Here are some of our most popular wideband 2 sensor products:

Shipping & Customs:

Do your prices include sales tax? What about VAT?

Prices do not include taxes. Orders inside the state of Georgia are subject to a 6% sales tax. We do not collect taxes on orders to other states or international orders; there is currently no national US sales tax. Most international orders are subject to tariffs or taxes upon arrival. This is collected by the government in the country the order was shipped to, and DIYAutoTune.com has no control over these taxes. We do not have the most up to date information on these tax rates, either, so we recommend checking with your local customs office for the most up to date information.

Will you reduce the value of my order on the customs paperwork or mark it as a ‘gift’ so I pay less in customs duties/taxes/import fees?

We do get asked this frequently and we wish there was some way to ethically avoid these taxes and fees for our international customers but unfortunately there isn’t.  We must properly fill out all customs paperwork and include a receipt with your order.  We made a commitment early on in running our business to be 100% straightforward and honest in all of our dealings, with our customers, vendors, and even the tax-man.  We hope you understand and even find comfort in knowing that we’re committed in being 100% straightforward with you as well.  We do appreciate your business and will continue to strive to keep our prices affordable.  Thanks!

Other FAQs

Main MegaSquirt FAQ This is the main MegaSquirt FAQ, as well as the MSExtra Manuals. You will do well to become one with the MSExtra Manual. Let it flow through you.

Matt Cramer’s MegaSquirt FAQs Some may be a bit outdated as this was Matt’s FAQ from several ago, before he worked here, still good information to keep available though.

What Wideband o2 Sensor systems do we recommend?  You can find those right here.

Technical Articles that should really be a part of this FAQ, but would make it too huge!

product disclaimer