Just done mine, and whilst I thought originally it was impossible from the top - it's not (unless you're doing it the hard way!
) and i'm a COMPLETE novice when it comes to fixing cars!
Disconnect battery (negative first)
Disconnect MAF sensor (black plug connecting to the air intake pipe just to the side of the top cover)
Undo the Air Intake Pipe from throttle body (if you follow the pipe to the back of the engine, that silver block it goes to is the throttle body)
Unplug the two big connectors on the top of the throttle body and one on the bottom of it
Remove the throttle body (mine had 4 torq bolts holding it in)
Now you should be able to see down the back of the engine (yes this is the space you have to work with
), you will see the starter motor directly below (silver cylinder with BOSCH written on it) and the good part? the crank sensor is UNDER that
Do not try to reach along, over and under the starter motor, you'll never make it; instead, reach around the cables between the engine and dashboard side of the engine bay.
This will allow you to get straight under the starter motor, and you will be able to feel the allen key bolt and end of the sensor.
Undo the bolt (patience required here as your arm will be aching a bit and it will probably be very tight so be careful not to ruin the head of the bolt
) and with a little twist from side to side you should be able to free the crank sensor from its socket and pull it out.
There's a little rubber O ring that goes around the sensor as well - make sure you have this too as it will most likely get stuck around the edge of the hole it was in (easy to pull out).
Once you've done all that, fitting is just the reverse
There's 2-3 cable clips holding the crank sensor lead down as well (brown connector at top of engine), these are a bit fiddly to get off as well
If you want to re-visit my go at replacing it - the thread is here! -> http://www.alfaowner.com/Forum/alfa-...roke-down.html