59 c4 1.6 vtr leak off pipes

[wotwot]

my sons c4 grand picasso vtr 1.6 diesel threw up the depollution fault and then blew one of the leak off pipes off and chucked diesel everywhere.
he put it back on but will then blow another off. seems there is a big build up of pressure on the return pipe not allowing it back to the tank (or wherever it goes)
after this happens he gets 2 faults which is a MAF fault and a turbo fault both of which go when the pipe is put back on.
any help or pointers would be great.