if you still have constant spark, it's not anything from the ignition coil to the distributor. the distributor and rotor are fine. Since you are getting constant spark, your wires and everything else electrical is fine there is no need to replace any of those parts. The problem is all mechanical. Since your BMW has a distributor system, there is a thing called dwell which has to do with the timing that your engine fires at. If the dwell is too short, you will have misfires or no fire at all. There is a tool you can get that measures dwell and you can time your car so that all cylinders will fire and fire correctly. There is a "cheaper" way to do it. and you can turn your car on and turn the distributor left, till the car runs really crappy, then turn it right till it runs really crappy and find the middle "crappy" point. If that doesn't work, then get the dwell tool or just take it to your nearest shop and tell them you need your dwell fixed.
"You gotta have a passion. If you wake up every morning doing what you love, you'll never work a day in your life."