07, 6.0 Wont Start..........

[tourerjim]

Hi from UK, new to the forum because ive searched google to no avail, I work for a garage that dabbles in American Pickups & have a 2007 Ford 6.0 Powerstroke Diesel that just wont start, its been on the ford diagnostics & there's no codes & all diagnostics test where within test guidelines.
When you first turn the key on you here the injector clicks then if you go to start its like it starts to fire on 3 cylinders & just as you think its going to start the cylinders drop off then if you wait few second & go through same start up process its just the same no matter how many times you try it.
Because it wouldn't start when they used the ford diagnostics the only thing they couldn't test was the crank & cam sensor so we changed them but made no difference.
Anyone got any good thoughts on this.???