Hi folks having problems with a 2008 r56 cooper d,we replaced the engine and turbocore about 6 months ago never regained the original power i thought the replacement core was the issue so last week i installed a known good turbo complete and new intercooler still the same total lack of power,struggles to accelerate in all gears with hardly any boost.

All the turbo oil lines gaskets,banjos,seals etc were replaced but the car is still struggling there does not appear to be any leaks from the turbo hoses or manifold can't figure out what could be the issue all i can think is the car was maybe remapped at some stage before i got it and the ecu map is thrown off with the new engine and turbo ?

also the car is not throwing any error codes at all just really weak performance

any ideas guys i'm new to turbos so have little info or experience to go on