My '99 GT suddenly became difficult to start. Sometimes it takes 2-3 times of cranking it before it will start and backfires before finally firing up. Once started it runs fine. I have replaced the fuel pump and filter,had a proffessional fuel system cleaning,had my Ford dealer run an injector leak down test which it passed and than checked each injector one by one for leaks and could not find any problems. 2 out of 3 times it starts just fine the first crank and than all the sudden you go to fire it up and the problem is back. Any suggestions would be greatly appreciated.

Also forgot to mention when it does backfire the fuel load smoke comes out the right side pipe and that it seems to be worsein hotweather.

 

Any suggestions?