EFI Conversion

I heard somewhere that carburetors are semi-controlled fuel leaks. Kind words. I grew up with carbs and hate them. Tuning, cracked floats, bad/ dirty jets, old gas gumming things up, etc. I was an early adopter of Megasquirt and am a huge fan. There is a lot of competition now and you should pick the system either you, your mechanic, or dyno tuner feel most comfortable or can just get the best deal.

Regardless, one of the first things I did after getting the 2002 home was rip out the 32/36 weber and manifold and start collecting parts for the conversion (primarily from the E30 318). I will not go through the whole process as there is a lot of better guidance out there but I will address a couple key points with my conversion. Please email me if you have questions.

Tachometer Input

The original tach signal comes from the coil negative post. I tried the “diode solution” without success. Finally, I followed the solution described by AustrianVespaGuy on the FAQ and the capacitor on EDIS#11 worked. Check out his Megasquirt posts! They are very helpful.

Idle Air Control (IAC)

For the IAC, I used the adapter from 02Again, a Jeep stepper motor/ valve and wired it as follows tp MS pins 25,27,29,31.

Power Distribution

My car has a 12-position fuse block which I modified to use a 10-position ATC/ ATO blade fuse block. This allowed for a main power fuse to the MS but not for the ignition, injector and fuel pump fuses needed for EFI. Originally, I installed a combo fuse and relay box I found on Amazon but was unhappy with the quality (flimsy, loose connections, difficult to troubleshoot).

The combo fuse/ relay block looked OK but the quality was not acceptable

Rather than gamble on another fuse/ relay block, I bought a fuse block and some relay holders from Autozone and mounted them on an ABS plastic sheet. Not the most elegant solution but much easier to install and troubleshoot.

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The current Megasquirt versions will easily drive a coil pack in a wasted spark setup but I used the Ford EDIS on previous installs and had the pieces in my parts stash. I mounted the driver to the firewall and the coil pack to the distributor plug. The plug and the toothed wheel on the crank were sourced from 02again. I am not sure he still sells them but believe Ireland Motorsports now does.

In the future, I will likely remove the EDIS module, drive the coil pack from the MS and move the coil pack to the firewall. I have had some (typical) oil leaking down the backside of the engine and suspect either the distributor plug or the port to the oil pressure sensor but they are very difficult to access in the current configuration.

Throttle Position Sensor (TPS)

For the TPS, I used a Bosch 0280122001. These are readily available online and fit the shaft of the E30 BMW 318 throttle body I used. The only issue is clocking the TPS to correctly read the full range and a spacer as the shaft is a bit longer than the TPS is wide. I designed and 3D printed a spacer that also rotated the TPS into the correct position.


The base tune that Tuner Studio and Megasquirt start with for the basic BMW configuration should get the car started. You will then need to do a little work on the fuel, AFR target and ignition maps. Again, the base maps will work and there are a lot of “go-bys” out there but everyone’s install is a bit different and you should really tune to your specific car. I am a big fan of the EFI Analytics Tuner Studio and the autotune function. Generally, you get the car warmed up, start logging, turn on autotune and start driving around. The program will modify your fueling values based on your AFR targets. For ignition, try to find a curve from your original distributor to match then modify as needed.

My current maps as of June 2021 follow (open in a new tab for a bigger/ more readable size). Be careful as each car is a little different and mine in particular is also turbocharged.

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