m42 on 55 pin diypnp megasquirt ms2

[downforce22]

I picked up a spare 55 pin megasquirt from diypnp designed for a stock m20. I pulled the cover off and it has 3 BIP drivers for wasted spark on a 6 cylinder.





I also have an m42 318is and am hoping to get the car running on the ms unit. I have looked over the wiring pinouts and it looks like for the most part I can get the m42 to run on the ms unit. There are a couple of problems I have found that I need to address.

1. Ignition system - The m20 uses a single coil while the m42 uses 4 coil packs. I only see one pin for the coil from the m20 pinout while the m42 needs either 4 individual drivers or 2 drivers for wasted spark. If I do wasted spark, how does the ECU know which coil set to fire? Is it via the cam sensor on the m42? How do I determine which input the ms unit is expecting? Do I need to change wiring to make it work or can I just select the coil on plug option from the ignition menu?

2. Cam sensor - Do I need to wire in the cam sensor? The m20 obviously works without one but uses the cap and rotor. What signal is the ms unit looking for my engine?

3. Knock sensor - The m42 comes with an knock sensor on the e36 motor, if i have to add something for sequential ignition, should I add something for a knock sensor? Where do I install that?

Besides that, I think I can just compare the m20 pinout to the m42 and link everything else together with an adapter, right?

[bmwman91]

1) It looks like there is a space for a 4th coil driver on that board, so maybe consider adding it. You will either need to drive all 4 individually, or switch to a different coil pack that was intended for continuous wasted spark operation. The M42's coils will probably not last all that long in a WS setup since they will be working twice as hard as designed (the stock ECU will run them in WS when the cam sensor signal is lost, but that is supposed to be temporary). The crank sensor + 60-2 wheel on the damper determine which pair fires by reporting TDC, and the cam sensor is what is used to determine the individual cylinder to fire by indicating whether cylinder 1 is in its compression or exhaust stroke.

The wiring harness aspect is going to be a lot of work. First, the M42 uses an 88 pin connector, so there's that. Only 43 of the 88 pins are used if I remember correctly, so in theory you could remove the terminals from the 88 pin housing and try to stick them into a 55 pin housing. I think that the pinouts may be different enough that some connections will be a direct swap (important ones like some of the grounds and such).

2) Yes, you should. It is the same type as the crank sensor...variable reluctance (VR). You may need to make mods to the MS board to work with it. There should be sufficient documentation in the MS community on how to configure the VR electronics.

3) You do not need the knock sensors, but they are nice to have. As far as I know, the E36 M42 ones will bolt right in since the block casting is identical. However, there is no provision for these in the stock wiring harness, so the wiring and MS mods are on you.


Make a table of the M42 and M20 ECU pinouts and see if everything has an equivalent or can be worked around. Why do you want to run a MS system though? If you are keeping the engine internally stock and naturally aspirated, there's very little to gain in terms of power. A chip will give all the possible benefits there, plus costing less than the ECU conversion. If you are in it just for the learning and fun, then that is fine, but the performance upside here is limited.