My M42 Powered E30 recently died in similar fashion.
After reading this thread, I went out and checked the resistance of the Crank Position Sensor, and it read high. I traced the wire from the plug (under intake manifold) down to the sensor head and found that the wire was rubbing on a pulley and wore through...
Now, can anyone point me to a reputable online vendor that sells the Crank Position Sensor for a reasonable price? (The Cam sensor is easy to find, but Crank Sensor seems elusive). It's part number 12-14-1-721-968
Someone linked BAVauto which has it listed for $155. Is there any place that has it for less?
Pelican Parts lists it as a special order part, at dealer pricing of $177
On a similar note: Here is the Real OEM diagram that has the part number for the Crank Postion Sensor
(Item#11 "Pulse Generator")
http://www.realoem.com/bmw/showparts.do?model=AF93&mospid=47305&btnr=11_0156&hg=11&fg=10