corsa won't star

Hi i have just replaced the evotec engine and ecu in my corsa, (1997)i had the timing belt done,and the new engine ran ok, my son has come
home and revved the arse off it,when i turn it over it gets to the point where it going to run, but then just stops. i have had it in the garage, the sparks ect are ok, they have checked it on the computer, everything fine with that,and they are at a loss as to why it won't start any clue as to what the problem could be. thanks Nyree
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