Im going to start dismantling this car in the next few days,but would ideally like to get it running first.
It turns over,sounds like its firing occasionally,but wont start.
Pedal trick shows spanner light constantly flashing (is that immobiliser issue ?)
Known good crank sensor fitted.
Petrol is being pumped up to the fuel rail ok.
Not going to spend a lot more time on it,but am curious.Normally petrol + good crank sensor means they will run ime. 
If it is, you need to go through the motions, ie Key out off ing., open door, lock, un lock door key in Ing, again all with the right Key and Chip otherwise it wont start even with the correct Key and Chip.
If that makes sense.
That's not right. No amount of sync'ing a key like that will make the chip in the key talk to its immobiliser ECU
The fact the car has started is shear coincidence

Its not sync'ing, its a restart thingy, if there is an issue with the Transponder Chip talking to the ECU then it will refuse to start, even if the problem has cleared itself, untill you go through the Lock up and Unlock motions.
Ive had it before a couple of times, and thought it may pay off for Albs, which it seems to have done. Not to say it may not come back and haunt you though.
I'm still sure it was a fluke
. As fas I know, no communication with the immobiliser won't stop the car from initially starting ....... it just stops very soon afterwards, or at least that was the case with an Astra that SWMBO had when I had a new key Tech II'd for it.
In my experience of the FL Migs, it wont start, just turns over with flashing EML.
Example, 2 keys in your pocket for the same Car, one has a missing Chip, try and start with the missing Chip, wont start, realise what you have done, pull the working key out of your pocket and try and start, still wont start even though its the correct key, go through the lockup procedure, car starts.
When Albs mentioned flashing EML and not starting, thought it might be worth a shot.
