MS1 Fuel only - Stock ECU controls spark through Coil/Dist

[bluej]

Hi all,

I have an MS1 V2.2 board that I've had for years now that I'd like to finally put to use on my recently low pressure turbocharged '86 325e e30 bmw.

End goal is a squirt n spark setup using the LSx COP's I already have, but in the mean time I need to get it up and running on fuel only as soon as possible.

I've been reading and researching megasquirt systems for years now, but still have some basic questions for planning my install.

First off, it seems the easiest way to get up and running would be to setup the MS in a "piggyback" mode and leave spark up to the stock ECU, pulling engine timing from the single coil. The question is due to the nature of how the stock ECU controls ignition. The six cylinder e30's have a rotor/distributor attached to the end of the cam, with a "swipe" type of contact on the rotor. The ecu grounds the stock coil for spark signal, advancing/retarding as necessary, which the swipe nature of the rotor contact allows for.

Does that mean that I will not be able to use that signal for engine timing to control fuel? I understand that with batch fire, the timing isn't quite THAT critical, but I don't know if the variance due to the ignition advance/retard is something that can be tuned around.

If it's a problem, the later versions of these motors use a crank trigger wheel/sensor setup behind the crank pulley that is easy to retrofit, and I'll eventually be going that route. Not having to source the parts yet would allow me to get the fuel-only setup up and running sooner to be safer than the rising-rate fuel pressure regulator that I currently have installed.

Thanks so much!

-Josh

[bluej]

OK, so I may have answered my own question. It sounds like I can pull rpm from the stock tachometer signal from the stock ecu and set the input for hall/optical. Is that correct? Not sure why I didn't think of that before.

Thanks!
-Josh

[trakkies]

The more usual way would be to simply take a feed from the coil negative. Instructions on how to configure the opto input for this in the manual.

[bluej]

The more usual way would be to simply take a feed from the coil negative. Instructions on how to configure the opto input for this in the manual.

Coil negative timing would be variable based on the stock ecu controlling ignition through the coil. It cannot be locked like a mechanical/vacumn advance and it needs to not be for proper timing control anyways. My question above was if that will matter since the actual rpm seen by the MS will vary from true crank speed based on the stock ecu adjusting timing.

[trakkies]

For fuel only control, all MS needs to know is the RPM. It might be ok to derive that tach feed from the rev counter feed from your ECU - I dunno. But from the coil is the tried and tested way.

[bluej]

What do people do when pulling rpm from the coil does not match actual rpm? Do they have to find a different source, or does it not matter because the variation doesn't effect tuning?

Thanks for responding.

-Josh

[trakkies]

That would be CDI or similar? Most ignitions systems are covered in the manual. If you have an odd one which doesn't supply a reliable trigger from the single coil it would be best to post details. A reliable tach signal is essential for the correct operation of MS running fuel only.

[bluej]

It's an IDI type single coil ignition, but with the stock motronic ecu closing the circuit on the coil for ignition timing and a distributor rotor setup in such a manner to allow for variable ignition timing.

Engine bay (not mine, but the same) w/ coil at the bottom center and wire to distributor at end of cam.


Rotor inside that bolts to cam: