Introduction & Parts needed | Part 1 - Gutting the box
Part 2 - Building the MS/Motronic Box
Part 3 - Getting it working
The popular Motronic 1.3 Engine management unit, was used by BMW, Audi and Porsche during the late 1980's and early 1990's.
It's
a reliable system, but compared to modern day standards, it is rather
outdated, with limited scope for improvement. The good news is that
the heart of the system, the ECU, can be exchanged for something more
modern, whilst keeping much of the existing wiring, sensors, injectors,
and coil as they are. Only one component need to be replaced (Throttle Position Sensor - TPS),
and one component added (Air Temp Sensor - IAT), both of which can be found at a
scrap yard, or purchased new. Any other extras, are purely optional. Changing the
ECU can be done in three ways. Rewiring the engine loom, splicing into
the existing loom, or going for the "Plug 'n Play" option, of converting
an old ECU box, ripping the guts out, and putting Megasquirt in it's
place. This article looks at the Plug 'n Play approach.
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| About this guide Having converted several BMW E30 Motronic systems over to Megasquirt, what is written here is my prefered way of doing it. I have developed two small PCBs which make the job easier, but thay are not essential, and you will see alternative ways of doing it during the guide. A kit, with all the bits shown in this guide can be purchased from me at shop.diyefi.co.uk
Parts List Scrap 55-pin Motronic box
MS V3 or V3.57 board with vertical DB37 connectors (vertical DB15 on 3.57 board)
Wiring loom - preferably multicoloured, to MS spec.
DB37 solder socket.
DB15 solder plug (V3.57 board)
2 x Fuse holders & ~2 & 20 Amp fuses
3 x Diodes (1N4004 etc)
5 x M3 Hex Spacers 12mm (max)
8+ x M3 screws, bolts, washers. (Torx or whatever)
2 x M4 nuts/bolts (for ground connections)
4 x M4 ring terminals (yellow crimp/solder type)
Heat shrink (various diameters).
Various bits of wire Optional:
Spark Drivers, resistors (Wasted spark/COP)
PowerPole or other connector (Wasted spark/COP) (plus nuts bolts)
3-wire Idle Control circuit board (see below)
LED & resistor for Fuel pump indicator. (helps with diagnostic) Parts are availabe from shop
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Idle Control Value
You can run the engine without one, but it will probably be hard to keep running when it's cold.
The Bosch 2-wire idle control valve (M40/42/43/44/50), works with little or no modification. If your using the Megasquirt V3 board, you will require a higher output driver. See here for details. Users of the V3.57 board can use the FIdle output without modification.
Bosch 3-wire idle control valves require an additional circuit, to provide the push-pull PWM arrangement. DIYEFI.co.uk can provide a circuit/pcb to do this.
Spark options Option 1 - Standard coil & distributor
For
standard spark output, you may use the stock coil and distributor.
Just connect Megasquirts single spark output to Pin 1 of the motronic
connector. Option 2 - Wasted Spark (solid state)
Wasted
spark uses one coil for every two cylinders (two on a 4 cylinder
engine, three on a 6 cylinder engine). By operating in wasted spark
mode, you can move to a soild state system, and thus eliminate the
distributor. Doing so, boosts spark output, and removes the need to
replace costly distributor caps in the future. The extra setup cost,
may be cheaper than replacing those caps! Option 3 - Coil on Plug (solid state)
Requires more drivers, and more coils. Little to gain from Option 2, but if you already have the parts, its worth pursuing. | 
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Tachometer Unless your opting for the Standard coil output, you need to get
the teachometer signal directly from the meqsquirt board. This
requires a transistor, and resistors. The output must be fed into Pin 6
of the motronic connector. Our Multi-IO board takes care of this for you. | |
Megasquirt V3 & 3.57 board
The Magasuirt 3.57 board is preferred for this project, as it has the additional DB15 connector which makes the job easier. If you purchase the board from us, we will pre-wire and configure the board accordingly. However, the V3 board works just as well, but you may need to hardware the connections, or use your own connector. Full wiring details details are given later.
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