As a newby to ford and turbos I was looking for advice to curing this problem.I run a fiesta xr2i with a frst engine and box fitted with a t3 turbo,the car is caged up and stripped internally.Took it to Cadwell park and found it would do a couple of laps and then would start cutting out at 4k,gently accelerating above 4k it was ok but hard down it was missing although it was more like the engine was being switched off.I realise I have plenty to learn about these engines and turbo charging.Not under load the engine would rev cleanly and does not overheat and the boost gauge shows about 12psi.Thanks for reading Dave