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″.

MegaSquirt Tech:

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.

Don’t I need sequential injection to make big power? Does the MegaSquirt offer this?

Sequential 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 at these low engine speeds.

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.  We’ve dyno tested several cars with using batch fire and sequential injection on the same motor. Peak power was the same without using individual cylinder tuning. However, the sequential fire setup did run a bit more smoothly at idle and at light throttle angles.

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.

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 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.

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.

Note– All parts are sold for OFF ROAD RACE-ONLY ground-vehicle use only. Aftermarket EFI/EMS systems are not for sale or use on pollution controlled vehicles. Alteration of emission related components constitutes tampering under the US EPA guidelines and can lead to substantial fines and penalties. Your state/district may also have specific rules restricting your tampering with your vehicle’s emissions system. In short, as stated before, our official policy has to be RACE or OFFROAD USE-ONLY in ground based vehicles ONLY.

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 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.

Idle Air Control valves versus 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 it’s stock ECU, 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 FIDLE 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 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.

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?

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…

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

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.

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:

Why 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?

A wideband o2 sensor system will give you far greater tuning ability than a narrowband sensor.  The problem with a narrowband sensor is that it is only truly accurate at 14.7:1 AFR.  The factory will 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 ‘stoicheometric’ (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, you car comes tuned from the factory for reduced emissions and that’s why that narrowband sensor is there.  Therefore it 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 (NA) or richer for forced induction, and the narrowband won’t tell you anything useful at that range.  Likewise at cruise you may not want to tune for 14.7:1, maybe you want better fuel economy at cruise and you want to tune to 15.5:1 or even a bit leaner possibly. Only a wideband 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.

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.  A narrowband can only tell you when it’s 14.7:1, and is therefore nearly useless for tuning.

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.

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.

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.  If you lost that or need a copy of it for some reason you can download it here:  LM-1 Quick Start Guide
LM-2 Quick Start Guide

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 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

Shipping & Customs:

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!

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.

Click here if you have a question you don’t see answered below.


Is a DIYPNP fully assembled?  Do I just plug it in when it arrives?

The DIYPNP ships in kit form and allows you to build a Plug-N-Play EMS for an incredible number of vehicles with more being added all the time.

 The DIYPNP is a brand new product line that bridges the gap between the MegaSquirtPNP, which is a fully plug-n-play MegaSquirt based product, and the traditional MegaSquirt kit. DIY preceded PNP in the name of the product specifically to help communicate that, it’s a brand new product aimed at the DIYer who would like to build their own PNP ECU that then plugs directly into the factory wiring harness of the vehicle.

If you would prefer wiring to ECU building, then the traditional MegaSquirt ECU route you suggested may be more for you. If you would like a PNP ECU and we offer a MegaSquirtPNP for your vehicle then great, just pick on up, plug it in, and fine tune it!  If you however prefer to leave your OEM wiring harness in tact and would like to build your own PNP ECU that plugs right into it, then the DIYPNP may be more your style. Not to mention we’ve added several extra hardware features to the DIYPNP.  You can run full sequential on a 4cyl or semi-sequential on up to 8cyl’s with a very affordable plug-in module available here ($38 upgrade). You can run sequential COP ignition on your 4cyl even if it didn’t come with COPs from the factory. You have built in boost control, launch control, table switching, flat shift, and more.  (See feature list for full details)

One of the most exciting aspects of what the DIYPNP brings to the table is the simply massive number of vehicles you can fit it to, allowing you to build a fully plug and play EMS for more than 60 vehicles now, with more being added very soon.

What is a DIYPNP?

The DIYPNP is a Do-It-Yourself Plug-N-Play Engine Management System. It is made up of three main pieces that allow for an incredibly flexible and modular system for building a plug-n-play EMS for a plethora of vehicles.  

MicroSquirt Module – At it’s core, the DIYPNP is based on the MicroSquirt Module which is a MegaSquirt-II Processor based ECU on a credit card sized PCB. The DIY element of this EMS comes from the fact that you assemble it yourself from a kit of components, soldering the unit together and then adding wire jumpers to route the signals to the connectorboard to match the needs of your car. The assembly is not nearly as complex or time consuming as a standard MegaSquirt ECU kit assembly, there are fewer components and all components are sized so that they are easy to solder (no tiny transistors here).

Mainboard – We’ve taken the awesome capability of the MicroSquirt Module, combined with the MS2/Extra firmware, and built out a mainboard that adds a very nice featureset including pretty much everything we get asked about on a daily basis by our customers. You’ve got dual ignition inputs and up to four ignition outputs (hi or low current, allowing for Coil-On-Plug for up to a 4cyl engine or wasted-spark ignition for up to a V8 engine. Distributor based ignition is of course supported as well. Knock control, boost control, 4 spare inputs and 4 spare outputs for driving fans, intake butterflies, on/off variable cam systems, whatever else you can imagine. There are more features too, check the features and documentation pages for full details.
Note– All of the primary Inputs/Outputs are brought out along the edge of the mainboard that lines up next to the connector board.
All common ignition input/output pullups are as simple as they could be with a resistor network in place ready to setup.

Connector Board – And then the last piece you need to know about is the connector board. This is a small PCB that slides into the same slot as the mainboard and lines up right next to it. It’s usually not much more than a breakout board for an OEM style connector that often fits a stack of vehicles as many of these connectors were used by multiple manufacturers, and often on multiple vehicles/engine families at each manufacturer. Sometimes we may fit an extra circuit on the connectorboard if we’ve found that the vehicles that use that connector typically need a particular circuit. An example of this is the Bosch Motronic 55pin connectorboard, which hosts a circuit to control the 3-wire IAC valve that is common in vehicles that use this connector.

So after you handle minimal assembly on the mainboard, you do a bit of research on the harness pinout in your vehicle (or download a spreadsheet of pre-researched info and just check it for accuracy in your application), and you use this info to run a handful of jumper wires from the mainboard to the proper breakout pins on the connectorboard bringing the signals in/out on the proper pins on the connector. This is what makes the DIYPNP so easy to apply to such a broad range of vehicles. It’s basically a set of PNP EMS building blocks, with awesome results.

You want boost control, run a jumper to the input and to the output. Turn it on the in the software and tune it.

You want to convert your engine from it’s stock distributor to wasted spark or COP, add the proper crank/cam trigger wheels to the engine (you might have what you need already inside of that old distributor) and wire those sensors up to the DIYPNP, then wire the ignition outputs up to your coils, set your timing and tune it.

The flexibility is massive. And if we didn’t include a circuit you want, we’ve got two large proto areas on the mainboard (one is under the uS Module) and in some cases there is a third proto area on the connector board if we had the extra space.


Is a DIYPNP better than a traditional MegaSquirt EMS box for my needs?

In short, a DIYPNP will do everything a standard MS2 will do, but has many extra hardware features built in to utilize features in the MS2/Extra firmware that normally you’d have to modify a standard MS2 to handle. In some cases those mods would be pretty extensive, but the DIYPNP makes it easy. Sequential injection and COP is a cakewalk. 2nd Ignition input, 4 ignition outputs, Boost control, launch control, flat shift, extra general purpose inputs/outputs, all built right in. There’s more too.  Check the features list here.

And oh yeah, it plugs right into your factory harness and looks clean too ;).


Do you offer a DIYPNP kit for my car/engine?

We’ve got a fairly long list of the vehicles and engines the DIYPNP kits we currently offer will support on our Available Models page here.  Keep in mind that just because your vehicle is not on the list does not necessarily mean that it won’t fit, it might just mean we missed your car and didn’t realize we need to add it to the list.  You’ll notice on that page that there are images of the connectors included with each kit, take a close look.  If the connector will fit your car then there’s a very good chance we can help you out.  Shoot us an email and we’ll help you confirm the ignition system on your vehicle is supported, and we’ll add your application to the list of supported vehicles as well.

Keep in mind when you’re comparing your connector that sometimes we’ll offer a connector that has more outlets on it than you’d need for your car.  For example, the 1990 Miata only uses the 22pin and 26pin plugs of our N76 connector, leaving the 12pin and 16pin plugs open.  The connector is a perfect match though.  This will be the case with other connectors as well as we will always base our kits on the connector that fits the broadest number of vehicles possible.  See the image below for an example of this.

DIYPNP ECU Connectors fit many vehicles in many cases

Click this image for a closer look if you’d like.

With all of the above said– if we don’t support your car now, and you want us to, you need to let us know.  Demand is what will drive which models will be released and in which order.  Tell us your year, make, model, engine, and if you’re window shopping or if this is something you’d be ready to buy right now if we made it. We keep track of this sort of thing and it does make a difference.


What will be included in my DIYPNP kit?

All of the parts needed to build your DIYPNP EMS will be included.

  • Machined black-anodized brushed aluminum case with DIYPNP Decal for the lid

  • The MicroSquirt Module

  • The DIYPNP Mainboard with all components to build it out completely in clearly labeled packaging

  • The DIYPNP Connectorboard along with the OEM ECU Connector you’ve selected for your application  (this is what will make the different kit part#’s unique)

    •  In some cases, there will be a few components needed for the connectorboard as well, these of course are included and clearly labeled for assembly

  • We even include the jumper wire and heatsink thermal paste needed for assembly.

Is the assembly difficult?

Difficult is a relative term, but for most even semi-mechanically oriented enthusiasts/racers, these kits are fairly simple to assemble.  In many ways they are far simpler than a standard MegaSquirt EMS to assemble and get up and running on your vehicle.  The part count is much smaller as compared to a standard MS kit, and there are not any components with tiny little closely spaced legs to give you fits.

What remains after the basic assembly is running a series of jumper wires from the mainboard to the connectorboard, basically connecting the 12v hole on the mainboard to the pin on the connectorboard where your stock ECU provides 12v.  Then you do the same for ground.  And for each sensor.  Beyond this there are a few jumpers to set to enable the ignition configuration needed for your vehicle, and a couple resistors to install if needed for your ignition system.

To the experienced MegaSquirter, this is a breathe of fresh air simplifying the process greatly.  To someone new coming into the process it might still sound a bit confusing, but don’t worry– that’s what we’re here for.  We’ve got an incredible support team that’s here 40+ hours a week for you.  That said, we’re fully intending to work our way through the application list, using local volunteers who bravely offer up their cars, and working out the exact pinout and ignition configuration you’ll need for a particular vehicle.  We’ll be documenting these and posting the information on this site.  As a part of doing this for these volunteers, we’ll also be getting the car started for them, and if they so choose, tuning it for them.  So we’ll have at minimum a startup map available, and in some cases a base map that is well tuned for the test car that we were brought, though it’s mods, and therefore mapping needs, may differ from your own a bit.


What if I’ve never soldered anything before?

You can do it!  It’s really not that hard.

There are a few basic rules:

  1. Insert each component, and bend the legs out about 20 degrees on the bottom of the PCB, this will ensure the part will not fall out when you flip the PCB over to solder it and will create a good mechanical connection between the component and the PCB.

    • In a perfect world, you’d clip the excess length from the components leads off now.  This will prevent you from stressing the newly soldered joint after you solder it.

  2. Make sure your iron is hot, and that the tip is clean and tinned.  You can clean the iron tip on a wet bit of sponge, or on a wet rag in a pinch.  Tinning the tip means adding just a tiny bit of fresh solder to the tip just before you touch it to the work.  This serves to sort of ‘fill the gap’ between the tip and the work, and transfer the heat quickly and completely.

  3. Press the soldering iron tip so that it touches the copper pad on the PCB and the component lead that you’re soldering to it at the same time.  This will heat both the component lead and the pad.

  4. Touch the solder to the opposite side of the lead and pad from where your soldering iron tip is pressed.  The idea is for the iron to heat the work (the pad and lead) and for the work to melt the solder.  The solder will wick into the joint (sortof just sucks into the hole and surrounds the lead completely).

  5. Once this happens, remove the soldering iron and let the joint cool for a few seconds without moving the PCB/component.  Inspect the joint to insure it looks smooth and shiny, not cracked/rough.  The solder should completely surround the lead in the PCB’s hole. You can always reflow the joint if you need to, you may have to add a bit of solder or remove a bit if you got carried away.

  6. If you didn’t already, clip the excess length of the leg off after the solder joint has cooled completely.  So long as you don’t distress the joint (don’t cut the soldered area but cut the lead just above it) you’ll be just fine.

  7. Yes, you can insert and solder many components at once, just make sure you don’t miss any of them (it can be easy to overlook a single joint when you have a lot of them in there needing to be soldered at once).



The maker of that video (linked from Youtube) also offers very affordable toolkits with everything you’ll need to start soldering.