Hi...
my mechanic has replaced both fuel pumps and the filter to cure an intermittent starting problem
but it hasn’t cured it 🤬......

i can get the car running by undoing the 12 mm HPFP nut and cranking the engine...
it squirts a bit of fuel....switch it off....then retighten the nut...hose down the engine and then, when I start it again it sputters into life with black smoke coming out of the exhaust
does anyone have any idea what might be going on before I send it to the main dealer??

its 250km away and with it been an intermittent fault I don’t know if it will fault whilst they have it

thanks
shoots