Ever since my engine has been built and running there is a overfueling issue that I can’t get to the bottom of spec is as follows:

205 block
7:2.1 low compression pistons
Standard head and cams
UtT38 turbo
Siemens 3102 55lb injectors
3 bar map sensor
071c plugs
MSD chip to suit
Fuel pump rewire
Twin fan rewire

i have replaced every sensor, had the TPS set up ,checked fuel pressure regulator, changed ecu even tried another loom (second hand) and it’s still emitting
black smoke out of the back when you rev it my next step is to check the fuel return pipe to make sure it’s clear beyond that I don’t know what to do? New engine loom? I want to get it set up on a rolling road and a custom map but while it’s overfueling I can’t get a MOT on it so I’m limited