simple test.... pull spark plug out put plug wire back on it and lay it on the exhaust or intake manifold or on anything metal that the spark plug will ground to... have someone turn the key and see if the plug sparks.... if you have spark then you obviously don't have fuel.... if no spark then it could be an ignition module, coil, bad connection in the wiring... the list goes on and on... sounds like your mechanic isn't exactly qualified to be doing the work tho.... mechanics shouldn't just throw parts at a problem they should be able to accurately diagnose and correct the problem.... maybe you should consider taking it to another shop and see if they can find a problem