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Blog: E36 318Ti Build: Microsquirt Standalone ECU

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E36 318Ti Build: Microsquirt Standalone ECU

Many 4cyl owners choose to swap their cars with the 6cyl engine because the conversion is essentially “drop in” when using the correct wiring harness, ecu, and hardware. It’s an easy way to boost the performance to essentially M3 level, but my goals are slightly different. I am concerned with balance, and more specifically, keeping the weight as low as possible. The M42 engine is a whopping 90lb lighter than an S52 engine, and this fact alone is why I am choosing to retain the 4cyl configuration for this build.

Naturally, I have decided to tackle the “Lack of power” drawback of the Ti by adding a turbocharger to the M42 engine. This will allow me to retain a significant portion of the weight advantage from the 4cyl, while pushing the headroom far past what is possible with a naturally aspirated S52. 


Now, before any of this can happen I need to sort out a few things. The factory engine management system from Bosch is sufficient for its age, but it will be a MAJOR setback when doubling or even tripling the air/fuel flow through this engine. The factory mass air flow sensor is a “barn door” design, where incoming air must physically hold open the door in order enter the engine. This will create cascading losses in flow energy as more torque is demanded.

The factory fuel system operates with what is known as “wasted fuel”, meaning the injectors are wired in as pairs and fire together; contrasted to “sequential fueling”, which means each injector is fired independently. Since "wasted fuel" results in slightly worse fuel economy, worse idle quality, and lower peak HP and TQ, I will be modifying the wiring harness to support fully sequential fueling.

There are many factory ECU’s that are capable of running a non-standard turbocharged engine with minimal custom wiring, but my factory system is too far from ideal, and I want to have full control over the tuning, performance, and safety of this engine. For this reason, I am using a standalone “Microsquirt” ecu. Many enthusiasts have seen the plug and play options that Megasquirt offers for a wide range of engines, but unfortunately nothing of the sort exists for the M42. The Microsquirt is the smallest module that the company offers, and is regularly used to run small engines found in ATV’s, motorcycles, boats, etc. In this chapter, I will go over how this system can be adapted to run a 4cyl engine with full sequential fuel injection.

Let’s begin with the ECU itself. The Microsquirt module consists of 50 main I/O pins, an additional 10 pin array, and two fuel injector drivers. Immediately it's clear that we have a hardware shortage, I need to run 4 independent injectors but there are only 2 outputs on the board itself. Fortunately, DIYAutoTune offers a sequential upgrade board which provides 2 extra injector drivers.



Now of course, this ECU could not possibly survive without some kind of protection, so my course of action is to hide it within the OEM Bosch ECU case. I sourced a “dead” ecu and began removing its internals.