Hier noch die DIY Loesung, damit sie nicht verloren geht.
Quelle:
http://forum.alfa145.com/index.php?showtopic=22853
How works the sensors in a motor twin spark?
There are two sensors in the motor, a magnetic pickup, similar a electric guitar pickup called crank sensor, and a hall effect sensor called the phase sensor.
The crank sensor let the computer count the theet and the phase sensor gives the zero position, boths to synchronize the sparks and injectors time.
When crank sensor fails, the computer can't count (the motor can't start), but when the phase sensor fails (frecuently due to dirt in movement) the motor still runing and starting with the broken sensor until you disconnect the battery, and the computer losses the zero position value, the computer can't obtain again the value as the sensor don't work. Then you think a lot of others things because the motor was starting fine!
Well, the phase sensor is expensive (at least here), but you can repairit with a economic component, a low cost hall effect sensor (less than $2), TLE4905 (could be even betrer: TLE 4924C
http://www.infineon.com/dgdl/TLE4924C_pb.pdf?fileId=db3a304332ae7b090132af75a28d013c)
You have to weld with stain the three wires to the three pins. Figure shows how to connect.
Then you must to fixit with epoxy, insert a plastic piece to let the space like original one, and remove when epoxy is hard. You can paint the plastic with oil to easy removement.
Then you can remove the excess of epoxy with sandpaper. Install and assemble.
Pictures shows how was rebuilt. A piece of wire was used to fix the small component in the correct position when the epoxy was soft.
The motor start, at last after a month! With this sensor: