The Mega Experiment: Part I – Skills & Starting

megasquirt_pcbStandalone Engine Management is not for the faint of heart. I’ve read a lot of forum posts where people become frustrated a few wires into their installation, fry stuff, and blame the people they bought it from. When in fact it was their own lack of understanding when it comes to automotive electrical and tuning. If I were selling and supporting these systems, I would almost have you answer a few questions before being allowed to purchase – but that’s me. 🙂

What should those basic questions should be?

If some of those four are puzzling, then it’s time to phone a friend, or carefully re-consider setting up and tuning standalone engine management yourself. Some people often suggest starting with a fuel controller first and moving into standalone later. I think that with modern cars (post 2000) this is sometimes more complex. For example: Just turning up the fuel is okay for a turbo add-on, but you have no control over spark and timing. This is why bolt on turbos simply up the fuel pressure or the injector size. The “We add air so we must add fuel” approach. Now the car idles weird and you have to trick the stock computer into thinking the fuel injectors are still under its control – when they are not. The fuel curve with throttle is fine, but idle and cruise can be excessively rich or lean depending on what the stock computer is expecting (or giving). Not really helpful if you’re looking to tune a naturally aspirated motor. Take over spark and timing and now you really have to trick the stock ECU. Modern computer driven cars are smart – a lot smarter than you ever thought. They average sensor readings and make lots of adjustments on the fly. If it doesn’t see the data it expects it might ignore a sensor and go into a limp mode, or shut the car down all together. 🙁 This also throws troubleshooting out the window.

The best example of this I’ve seen is changing the boost line “T” on a stock Subaru WRX with one that has no built in restrictor. The car now boosts to 16+ psi and the throttle response is immediate! That first full throttle run is the beginning of the end though. As manifold pressure is known to the ECU, it dials back the boost slowly, and after a day of “Holy shit my car is fast!” it’s back to 14psi stock and your changes are null. I’ve seen other internet tuners change the voltage of the throttle position sensor. Wide open throttle on MY car may be 3.9V and yours is now 5.0V – but again the first few times it adds extra fuel, is super responsive, and soon it will expect 5 volts for WOT and go back to the daily commuter it was designed to be. The Subaru ECU’s will just learn around sensor tricking (like the APEXi S-AFC) in a matter of hours. It’s almost frightening…

Once you control fuel and spark and know where the crank and camshaft is – and what the intake temps and coolant temps are… What are you keeping the stock computer around for? Gauges? It’s just too much of a hassle and a flashing CE light for speed and RPM. Need to go back to stock? Then make a wiring loom so that you can. Man up – go standalone 😀

Tools and skills needed:

  • Ability to solder, crimp, and heat-shrink
  • Read and understand simple wiring diagrams
  • Voltmeter / Ohmmeter / Continuity Tester
  • High quality crimpers / Pin connectors
  • An Oscilloscope
  • Patience

You’re tuning a modern car with modern signals and sensors right? The crankshaft, camshaft, and vehicle speed sensors are all a waveform. PWM circuits drive the Idle Air Control valve, boost, etc. There is almost no way to measure these signals without a scope. You don’t need a $600 bench model. A USB Oscilloscope or an inexpensive portable scope is more than adequate.

This helped immensely when I was diagnosing my crankshaft signal. The car refused to start and it could be 1 of 150 things. Being able to see a clean signal on my scope narrowed it down to a software setting.


Selecting the MegaSquirt
I’ve watched the development of MegaSquirt for a few years now. About 5 years ago it was suggested to me – and I felt at the time it was a bit of a “science experiment”. It was hard to setup sequential fuel and it didn’t have half the inputs and outputs needed to run a fully equipped vehicle. There were several boards and versions and at least 4 or five of the circuits had to be setup and soldered by hand. Some shops offered it as a service, but in 2007 it just wasn’t a mature product.

In 2013 the list of “standard options” on an MS3Pro or (MS3 with MS3X) is numerous. Sequential fuel and spark of 8 cylinders; AFR and VE tuning with cranking and warm-up enrichment; Idle air control, launch control, boost control, VVT control, etc. Advanced options like driving a second set of injectors, anti-Lag, and traction control come standard with no circuit soldering needed. Also the ability to do a plug and play on a lot of vehicles. Various communities continue to push development, MegaSquirt has a cult following with 1st & 2nd Generation Dodge Neon and Mitsubishi Eclipse owners (similar engines with the 420a) and the Miata Turbo forum has been a great source of info.

Other options included AEM and MOTEC. Certainly more durable, but also much more expensive. Tuning yourself is possible, but these are more closed source installs – where an “authorized retailer” or experienced tuner sets it up for your vehicle. Which in the end is probably the best option if you have no desire to mess with engine management. I wanted to take up the challenge, but I know I’ll still be paying for dyno time from an experienced tuner.

Next Up: What’s it like to remotely control your car with BlueTooth? It’s awesome! Especially when you can make it shoot sparks! Stay Tuned!



  • PWM is simply modulating a pulse of energy at the same voltage. Instead of varying the voltage, you change the duration and frequency (duty cycle) of the pulses. LED’s and Fuel Injectors typically only operate at 1 voltage unlike a lightbulb – so in order to dim them / vary the flow of fuel – you use pulse width modulation.
  • Ground your engine controller to your engine! This is critical for reading sensor information. Cars are extremely electrically noisy, and good grounding is key to success!
  • 14.7:1 Air to Fuel ratio for gasoline. (14.7 parts air to 1 part fuel) This varies with different fuels of course.
  • When you switch off power to an electromagnet (coil / inductor) the magnetic field collapses and creates a voltage spike (EMF) potentially many times higher than the input voltage. (12V spiking to 50V) Solenoids and fuel injectors are just electromagnets and without a flyback diode that voltage will not dissipate, and can cause damage to circuits.