Low Cost DIY EFI

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Low cost DIY EFI options for users who don’t mind putting a little elbow grease/solder into the project to save a bundle of cash.

Would you prefer to spend less money, and don’t mind putting in a bit more work? Do you enjoy the satisfaction of working on your own car? If you love the pride that comes from knowing you built everything on the car, you can even get a kit to build your own ECU from a circuit board and bags of parts!  If you don’t want to build the whole ECU, but still want a very affordable solution and don’t mind making a few changes to an off the shelf ECU to accomplish your goals, read on down lower on this page.

If this isn’t you at all and you just want a system that comes out of the box ready to wire in, or maybe even ready to just plug-in with no wiring required, jump back to the Intro of this section, or jump directly to the Wire-In systems, or the Pro/Plug-N-Play systems here.

MegaSquirt DIY EFI Un-Assembled Kits

DIYAutoTune MegaSquirt build-it-yourself kits are incredibly well documented, clearly labeled kits where every component is labeled with it’s component number (to let you know where to install it on the PCB), as well as how to bend the components leads to fit the board easily, and whether or not the component needs to be put in a specific way or if it can be put in either way (some components don’t care and can’t be put in backwards, others do, and we let you know which right on the bags they come in).  Additionally the documentation is very thorough, and walks you step-by-step through assembling your ECU, and stops along the way after major sections of the build to allow you to test the circuits you’ve built individually.  You build the power supply section first for instance, then you test it and make sure it’s getting 12v in like it should, and putting out 5v like it should.  Simple enough.  Next you install the processor and serial circuits, and then test basic communications through a simple loopback test we walk you through in the docs.  Next you install and test the inputs, which you can test yet again actually connecting to the ECU with the tuning software and manipulating the inputs (CLT sensor, IAT sensor, TPS, etc) with the Stimulator and seeing them respond appropriately in the tuning software.  Finally you install and test the outputs, again using the Stimulator to simulate different running conditions and monitoring the outputs to ensure they’re doing what they’re told to do.  It sounds a bit complex, and well, it is more complex that just taking the unit out of the box pre-assembled and wiring it up, but bottom line, it’s not to difficult for most anyone to master if they read the docs and take one step at a time.  Tens of thousands of people around the world have successfully built their own MegaSquirt ECU and run their engines on an ECU they built themselves.  And many of these individuals have gone on to successfully compete in a huge variety of motorsports.  It’s not too hard for you to build your own ECU if you’ve got a bit of patience and are excited about the project and what you’ll learn along the way.  Ever ‘painted by numbers’ before?  It’s truly that simple to follow the directions and build your own ECU, by numbers.

If you are looking for the lowest cost rock solid fully tunable EFI and Ignition control solutions available, you’ve found it!  If you care less about cost, but enjoy the project aspect and the appeal of building your own ECU and running your engine on it, again, you’ve found it!  If you like the idea of learning more about how your engine works and how it is controlled, and building that knowledge to intimately know exactly how to get the most of of your current engine and others you work with in the future, there’s just no better way.  You WILL understand you engine, it’s air/fuel/ignition needs and more, and you will learn how to get the most out of it.  These MegaSquirt DIY EFI kits continue to be extremely good sellers and customers have some incredible results running these systems they built themselves, and they had a blast doing it.

DIYAutoTune MegaSquirt Assembled ECUs

If you don’t want to build your own ECU but aren’t afraid of a little internal tinkering you can also order a low priced, Assembled MegaSquirt 1, 2, or 3 ECU.  In many cases, these will be good to go for your engine right off the shelf, and as such this paragraph really crosses over to our ‘wire in ECUs’ section, and you should read that next.  Contact us to discuss your specific needs, and if needed, you can DIY some minor soldering of additional components to add some ‘extra’ capabilities you want to run on your engine, or we can do that work for you, putting you squarely in that ‘Wire In ECU’ camp not having to do anything inside the ECU at all accept maybe adjust a dial or two to fine tune the system to your ignition pickup.  Otherwise, you just wire it up!

The DIY approaches discussed about all share a common thread – they’ll take a bit of research to determine what you need and will require you to know your engine and ignition system well (or learn it, which isn’t a bad thing), so they’ll be a bit of a learning experience.  Without a doubt though, when you put that effort into your system your results will be incredible and at the same time less expensive than pretty much any other engine management system option available.

OK, but which DIY MegaSquirt System is right for me?

This is the line that started it all. These are universal, wire-in systems that come in build it yourself kit form and as Pre-Assembled ECUs.  Prices range from just under $200 for an MS1 V2.2 with basic fuel control and not much else in kit form, up to nearly $700 for a fully assembled, ready to run MS3 V3.57 with eight channel sequential fuel, distributor-less ignition, and tons more options. They can be customized for different features as needed. We’ve constructed a page to explain all the basic MegaSquirt variants in more detail. Here is a quick comparison between the major versions, using V3.0 / V3.57 boards. This uses the current release code; some features may be added in later code updates.

MegaSquirt-I MegaSquirt-II MegaSquirt-III (with MS3X)
Firmware version used when making this chart MS1/Extra 029y4 MS2/Extra 3.2.5 1.2.3
Fuel control 2 channels, bank to bank 2 channels, bank to bank
Can be expanded to 4 channel sequential, but it’s not easy.
8 channels, fully sequential.
An additional two channels can be used for a second stage.  (8 sequential plus 2 batch staged)
Fuel precision 100 microseconds 0.6 microseconds 0.6 microseconds
Ignition control Up to 6 channels available Up to 6 channels available Up to 8 channels available
Idle control On / off, PWM (2 or 3 wire) On / off, PWM, stepper On/ off, PWM, stepper
Communication RS232 serial RS232 serial RS232 serial, USB
Data logging Through laptop Through laptop Internal SD Memory Card for on-track recording without a laptop, or optionally datalogging through laptop is also supported.

Note these are just the highlights– there are other things to consider such as the fact that MS3/MS3X have a large number of inputs and outputs that can be used for datalogging extra parameters and controlling more on your engine that the MS1 and MS2 don’t support.  This doesn’t mean the MS1 and MS2 can support many of the same features, for example, Nitrous, multiple electronic fans, Boost control, Knock control, sequential ignition, etc.  All MegaSquirt variants can support these, but the MS1 and MS2 might only have enough outputs to support a few of these options at the same time, while the MS3 with MS3X could support all of them at the same time and still have I/O to spare.  It’s quite the powerhouse, and more than some people NEED, which is why the MS1 and MS2 continue to sell so well for those on a tight budget, and they perform very well, there’s no bigger bang for the buck out there.  For those that have the budget to go MS3 with MS3X, you will love it, it’s the same bang:buck ratio, just a few more bucks for a much greater featureset (aka bigger bang!).

Also, you’ll see three different PCB’s mentioned, well, really just two on the DIY EFI kits.  There’s PCB v2.2 which is offered with the MS1 kits, it’s pretty bare bones but extremely cost effective.  If you want to though you can also build a DIY EFI kit running the MS1 processor on the PCB v3.0 which adds a few minor features and improves a few things in a manner that’s probably worth the few bucks more if you can swing it.  The MS2 and MS3 DIY EFI kits are only available with the PCB v3.0, so if you’re building it yourself you’ll be running that newer mainboard.

The v3.57 PCB you might have heard of is not offered in the DIY EFI kits but only in the pre-assembled ECUs (as it’s pre-assembled from the factory, and not as DIY oriented).  It’s very similar to the v3.0 PCB design, just designed to be machine manufactured using tiny surface-mount components instead of the larger and easier to solder thru hole components you’ll be installing if you build a PCB 2.2 or 3.0 board.

Our advice — don’t let the PCB version confuse you much– pick the CPU variant you want for the features you need to control your engine, and then if you’re building your ECU yourself from a kit, go with the v3.0 PCB unless you are looking to shave just a few more bucks off your DIY MS1 by going with the PCB2.2 to keep it as affordable as possible.

Then, we have accessories; here is a rundown of the ones you may want to consider.

Must Haves

Stimulator – This isn’t 100% required but it should be in our opinion, let’s say 98% if you’re building the ECU yourself, and 80% required (or recommended) if you’re buying a pre-assembled ECU. During kit assembly there are several sections that you complete one at a time and test the unit after each section. You will need the stimulator to be able to test the unit. After assembly, or if you buy a pre-assemble ECU the stimulator will help you to get familiar with the MegaSquirt and the tuning software before ever attempting to install the ECU on your engine. This is also an excellent tool for testing your Megasquirt ECU while you are working through building your wiring harness. If you have a problem and don’t know if it’s in your wiring of the ECU you can use the stimulator to figure that out, and if the worst happens and you see sparks fly, you can plug the ECU into the stimulator and make sure it ECU is still working properly so you know you can continue. While not an required tool it is highly recommended- we’ve seen many people come back for one with their project stalled in the meantime, and we’ve never had anyone regret buying one. If you don’t purchase a stimulator for yourself you should at least make sure you know someone who has one that you can borrow when (not if) needed.  We’ve never had anyone regret buying one, we’ve had plenty of people regret NOT buying a stimulator, and then place a second order for it. You can find a JimStim & power supply in the ‘Tools’ section of the catalog.  The JimStim adds the ability to simulate many types of OEM crank and cam sensors and test more outputs.  We recommend the JimStim if you’re going distributorless with a crank trigger wheel or any patterned crank or cam trigger as the JimStim can simulate most of these patterns and allow you to test and preconfigure your ECU as accurately as possible to meet the needs of your vehicle.

Tuning Cable – You’ll need this to connect your laptop/PC to your ECU.  It’s a standard DB9 Straight-thru serial cable, meaning pin1 goes to pin1, 2 to 2, 3 to 3, etc.  You can find it in the ‘Tuning Cables’ section of the catalog.



USB-Serial Adapter – If you’re laptop has a real DB9 serial port then you don’t need this.  If not then you probably do.  Many USB-Serial adapters are very troublesome when used with the MegaSquirt and MegaTune, we tested a couple to find one that works reliably every time.

Relay Board and Cable – Though the Relay/Power Board is not required, it is a convenience and reduces the chance of miswiring during the installation. The relay board provides a central place for all of the required relays, fuse protection, and external wiring for the MegaSquirt ECU. If you are installing MegaSquirt in a previously fuel injected engine you may be able to reuse all of your existing relays. If you are fuel injecting a previously carbureted engine you will need to install relays for the main ECU power, Fuel Pump, and Idle circuit. You can do this manually or you can use the Relay Board to simplify this process.  You can also build the cable yourself with the included DB37 and hood that included (one w/ the relay board, one with the ECU kit), or as the cable is kind of a pain to build I’ve made them available pre-assembled as well.   Note that the relay cable and the wiring harness are mutually exclusive- they are not designed to be used together as once you use a relay cable you just need to run all wiring back to the screw terminals on the relay board, not a DB37 connector like the harness uses.  I have had customers buy both just to harvest the labeled/color coded automotive grade wiring after cutting the DB37 off.

Lead Bending Tool – Makes life a little easier when building out the kits as it allows you to precisely bend the leads to fit properly into the PCB.  Our kit labels are marked with the proper spacing for each component eliminating guesswork.

Wideband o2 Sensor/Controller – Highly useful for tuning as this will display your exact air/fuel ratio accurately so you can tune appropriately.  Narrowband o2 sensors (OE on most cars) are ONLY accurate at 14.7:1 so they are nearly useless for tuning, wideband gauges are accurate from 10:1-20:1.  I have units with and without gauges.  The LC-2 is an affordable unit suitable for permanent in-car installation, or perhaps an MTX-L combination gauge / controller.  You can also buy an LC-2 with a gauge; prices in the two hundreds depending on what gauge style you prefer.  The LM-2 has a built in display and can be used for permanent installation in a vehicle but it’s better suited to someone who plans to tune multiple cars and wants a system designed to be moved from car to car.  The LM-2 also has the ability to read two wideband sensors and data log information from an OBD-II diagnostic port on most ’96 and later cars.  Both the LC-2 and the LM-2 have dual programmable analog outputs.  You can use one to drive a gauge, and the other to feed the ECU, or just use one or the other.  It will also simulate narrowband to fool the stock ECU and prevent CEL (check engine lights).  You can also buy Innovate gauges on their own if you already have an LC-2.

Trigger WheelsMegasquirt works with many distributors and crankshaft position sensors. But if you happen to have a trigger wheel that is not compatible, or if you want to use features your original trigger wheels do not support, you can use our line of 36-1 trigger wheels for a highly accurate crank trigger setup.

Wiring and Sensors

Our 8′ wiring harnesses are designed to be adapted to any engine. They are very nice and fully labeled (printed labeling on the wires) with split loom covering.  All wiring is automotive grade and the connector hood is metal.  MS3 units with MS3Xpander will need a second wiring harness; we carry a ready made one..  Closed element IAT/CLT sensors are available with a 6″ wiring pigtail, as well as open element IAT sensors for turbo/SC applications.  We choose to carry Fuel Injector Connection flow tested Bosch injectors.  Megasquirts have a built in MAP sensor, while the Microsquirt can use a GM 3 bar MAP sensor.

You can usually reuse your stock CLT sensor, and often the IAT sensor IF it’s still there when you remove the MAF/AFM. If it’s a part of the MAF/AFM then you’ll be removing that, and you’ll want to wire in a new one.

Also note that the relay cable and the wiring harness are mutually exclusive- they are not designed to be used together as once you use a relay cable you just need to run all wiring back to the screw terminals on the relay board, not a DB37 connector like the harness uses.  I have had customers buy both just to harvest the labeled/color coded automotive grade wiring after cutting the DB37 off.


 DIYPNP — DIY Kit based Plug-N-Play ECU — Build your own Plug & Play EFI System with instructions!

Interested in building your own ECU from a kit, but like the idea of not having hack up your stock wiring or rewire your car? The DIYPNP might be for you. This is just what it sounds like, a DIY PNP ECU.  You assemble the kit, and once complete you have an easy to install comes in a kit, but the assembly is somewhat simpler than a regular MegaSquirt.  You use jumper wires to make its pinout match the pinout of your stock ECU.  I’d say about 5 hours is a reasonable build time if you have a little soldering experience.  The DIYPNP sports an OEM ECU connector, letting you plug it into your original harness.  We currently have options fitting hundreds of different models for only $452.  You can read about the available models and featureset here if you’d like to take a closer look!


Although this one has more in common with the pro lineup in that you don’t build it or need to open up the case.  The versatile MicroSquirt can make it attractive to the hobbiest market too for less than $400.  MicroSquirt has become a popular entry-level controller for basic LS swaps, but was originally designed for power sports applications – watercraft, motorcycles, etc.  Its small size and rugged construction makes it popular with people who want an ECU that’s easy to put in an inconspicuous location, or racers who want an ECU that will stand up to harsh use, such as road racing or dune buggies.  This unit has two fuel outputs and two spark outputs, a PWM output for idle or boost control, and two on/off outputs.  It’s possible to reconfigure it to use the extra on/off outputs as spark outputs as well.  Although most users will have somewhere from one to four cylinders, it can be, and has been, used on V8 applications.