A5 B8 cranks but wont start

[SteveQ]

Hello Everyone

This is my first post .I hope someone can throw some light on my problem.

My A5 B8  3.2 fsi had been 

really good. Because of using it as a second car the battery started to loose its cranking ability. No problem it always started with a jump start.

I then bought a Topdon starter which seemed great.

But being in a rush one day I connected it with the polarity wrong. I dont think I pressed the button but could have.It obviously didnt start.

Since then the car cranks fine but wont fire.

I did find the pyro fuse was missing and the small connector had a resister added. I have reinstated both now and fitted a new alternator in case it has been damaged.

Obd eleven is not telling me much either

Any help would be much appreciated . 

 

[Steve Q]

Could it be an imobiliser issue? Any warning light on the dash? 

If it's not imobiliser then could it be an issue with cam sensor?