Hers a strange one No fault codes found but won`t start

Just got myself another fault code reader and when scan car it says not fault codes found. I will say that have taken off negative battery terminal so this is what gets rid of codes. Now have scanned it it shows no codes but turns over fires couple times then stops Trouble I think is really my limited knowledge of modern cars and how they work. If there were any faults they would have shown up after removing battery terminal and then re attaching it and turning on ignition , it should show up any faults. As it doesn`t then no reason for it not to start. plenty of fuel, sparks are good. new camshaft and crankshaft sensors but if these were faulty it would show up. Unfortunately me thinks as it at end of my knowledge its time to e-bay as spares or repairs. With all stuff have replaced, starter, battery seem a waste to scrap it if some one with better knowledge can fix and use it. Any suggestions as to problem would be greatly appreciated
 
Top