Megasquirt EFI (and EDIS) for the BMW 2002 - Part 1

[germancarguy]

So initially the question is spark control: Option1 is go with a the bluetooth 123 distributor and some OX sensor. Option2 is a microsquirt/ distributor-less system with a encoder pulley.  Option1 has limited expansion while being very simple. Option2 has more flexibility and expansion potential at the cost of complexity. Building the harness is not a big deal for me (not sure where to get all the connectors). And having to active O2 integration even if I stay with a carburetor will help with much more flexible timing configuration. If I choose to upgrade cam, pistons etc. I can decide where to go from there.

 

Paul 

[AustrianVespaGuy]

4 hours ago, germancarguy said:

So initially the question is spark control:

The major difference between the two is accuracy.  The 123 setup is great because it is very easy and does let  you program the advance curve, and I'd say this is probably the best option if your sticking with carbs.  It's really not in the same league as a crank-triggered setup though when it comes to accuracy.  What we're ideally after is to fire the plugs at just the 'right' time, meaning when the piston is at a certain height during its upward travel on the compression stroke.  Since we can't directly see where the piston is in the cylinder bore, we use crank degrees as the next best reference point.  There is still some slight error here due to things like connecting rod stretch, the tolerance between the wrist pin and small end bearing, and so on, but these are all pretty tight tolerance with small stackup, so without knowing exactly, I'd guess the stackup here adds up to something +/- 0.1 degrees of potential crank revolution 'slop' for a given piston position.  But to get from here to the distributor rotor, you need to then add in all the tolerances for the crank sprocket to timing chain, the chain itself, the chain/cam sprocket, any cam twist (this one's probably negligibly small), the helical gears between the cam and the distributor shaft, and finally any axial play in the shaft itself.  This all adds up to quite a LOT in the end.  Again I don't know exactly, but here I'd estimate it's probably a full degree when things are new, and probably more like 2 degrees with worn parts.  Oh, and then multiply whatever it is by 2, since the cam runs at half crank speed, so any error is actually doubled.  Watch the little timing ball bounce around with a timing light sometime; that's actually seeing this error in action.  But going to a crank-fired setup, we not only decrease the error by an order of magnitude, the resolution skyrockets because with 36 tooth wheel, the system is getting updated engine speed and acceleration input 32 times/revolution where as the distributor type systems only get this information at each ignition event, or twice/revolution.

So the question is how critical is that spark resolution for you?  If you're sticking with carbs, I think having a degree or two of error is no big deal.  Cars can still run just fine on points after all!  But if you are/planning on having a high frequency processor in your car to run, say, fuel injectors anyway, then you might as well take advantage of it to control your spark to ultra-fine accuracy also, right?!  The crank trigger wheel is absolutely FROZEN stationary when I put my timing light on it!

Edit: We'll see if this video helps.  Not greatest quality from my phone, but look how still the white timing on the crank pulley stays; no bounciness at all, that's crank-triggered ignition for ya!

Edited May 7, 2020 by AustrianVespaGuy

[germancarguy]

Closer to the final plan:

 

1) My 76 will need an exhaust system at one point, so I need a recommendation for a full replacement system with header (long or short ?) with a OX bung.

2) Install the OX sensor with readout.

3) Install the 123.Distributor and a new Bosh coil.

 

I am running a stock Air Cleaner with the Ireland Engineering adaptor and a 32/36 Weber.  And start the tuning !

 

Paul

 

 

[AustrianVespaGuy]

Update! Just got around to improving my air cleaner/intake setup and finally did a dyno run! Made a brief post in the forums about it but figured I ought to link it here also since it's pertinent to the whole MS installation information:

 

[sczapiga]

Great writeup! I know it's been a few years but, I purchased a MS3x setup that was already on a 2002 and it came with the same momentary button and red led that yours shows in the photo of the ecu mounting. What is this used for on your unit? I can't seem to figure out what it's for. 

Thanks