The art of fine-tuning an engine computer is viewed as one of the blackest in the aftermarket. Table after table of arcane numbers, weird figures, lambda this, AFR that, wastegate duty cycle etc…it’s enough to make one’s head spin. However, it’s also a necessary step in squeezing the last drops of performance from an engine.


MSEFI is basically a DIY engine management system as explained before, it is a unit put together by assembling a compiled list of components which when put together results in an inexpensive solution to engine management. Many users of MSEFI have also reported huge gains in gas mileage as well as drivability. Recently I had the privilege to work on a 1989 BMW E30. This was a completely stock engine 2.5L engine which the owner decided to turbo charge with a few parts which he proudly boasts he purchased on ebay (my type of guy). We decided to do the project together since he too was interested in the actual putting together of the kit. So while discussing it I asked what was going to be his method of engine management, then he gave me a box containing a wiring harness the length of the car and a black box with a serial port cord connected to it, no labels, no brand, no names…….. “what the fuck is that?” That’s what I thought, anyhow he mentioned the name and it struck a cord, oooooooooh shit! That’s Megasquirt? Modasss!

After getting over myself I was anxious to know more so I read up on it, did many internet searches and actually downloaded the tuning software “Megatune” and the datalog software “Megalog viewer” I started looking at the screen shots and messing around with it, looking at the screen tables, and settings.



It took me a whole month to get through all the settings and understand what they were for and the effects they had on the engine as a whole. We used MS-I V2.2, with 440cc high impedance injectors, (N.B low impedance injectors with less than 10 ohms require a special board or damage maybe caused to the U7 chip and or the injectors), GM coolant temperature sensor (factory sensor can be used accuracy may be a factor), GM intake air temperature used as well and LC1 Wideband 02 sensor (narrowband sensor works fine as well). Basically that’s all that was needed in order to run Megasquirt, only 7 of the wires from the actual MS harness were used.


This is a basic wiring diagram for MS, this is the step you follow once u have either received a completed MS box or completed your ms and confirmed that it is fully functional and ready to go. Alright the MS has a simple harness which is connected to the MS via a DB37 connection similar to what’s used on old school printers and computers.

Nuff said, MS can fire up to 10 injectors per driver, with two drivers that’s 20 injectors. However on the BMW for instance we had 6 injectors (it being an inline 6). Basically you group your injectors, injectors 2, 4 and 6 will be fired by injector driver 1 (light blue wire) and 1,3 and 5 by driver 2 wires (dark green wire on the right).

Next is TPS (throttle positioning sensor) ground, signal wire and 5v verify. You can later calibrate this on your MS via Megatune (tuning software for the Megasquirt).

Then your oxygen sensor, MS works with either Narrow Band or Wideband O2 sensors such as the LC1 or the LM1. The LC1 is not my personal favorite for tuning it might be cheaper but reading can be unpredictable so LM-1 is standalone wideband which is so good for tuning. We will speak about this further.

Now to hook up your IAT ( Intake Air Sensor) GM sensors preferred for their accuracy, the your CTS (coolant temperature sensor) GM Sensor preferred if not you would have to use software called easytherm to calibrate/make sensor correction. Then your tach signal to the negative terminal on the coil.

Connect your crank sensor, your fuel pump line and your grounds, to ensure best ground run all necessary grounds neatly to the negative to terminal for the best possible ground and less interference. The Map sensor inside the Megasquirt has to be ran into the vacuum lines on the intake manifold. This is the great part bout Megasquirt cars running AFMs, which are restrictive. Once this is complete put the car back together as you would normally.

Now to configure MS. You open Megatune, then go to MS configurator, in file menu, go to car1 then settings, open settings then settings code variant. Unset ms I and set msns-extra. Select your wideband type and set your Map sensor type (readings are in KPA, 1kpa = 0.15psi remember this cause 100kpa is 15psi or 1bar). Now you save those settings and open Megatune again. I think it is better to add in your constants and familiarize your self with the settings and set up before starting the car. I will post the rest of the set up later so you others can get ready to Megasquirt.