I have a 2012 tdv8 4.4
I've been told by my mechanic that turbo shut off valve on the big turbo is faulty, he's 30 yrs in landrover main dealers
He's been right so far anytime I've used him
She'll go into limp mode over 2600rpm
Can these units be reconditioned?
£700ish for the new part

Have you checked to see if the COSV valve is free to move? Between Rad and engine at the bottom.

No I haven't, is it a vacuum test

It's difficult to get to but yes. You should also be able to move the valve 90' by hand.
If yours has a nut on the end of the rod it is the old type. There is a revised part without a nut.
If yours is stuck try and free it off and see if it resolves your problem.

The big primary turbo is variable vane, and is on the right hand side of the engine. The smaller secondary turbo on the left hand side of the engine is the one with the turbo shut off valve mounted on the back of it. This controls the exhaust flow to the turbo as required. There is a video as I recall on LR time of the guy stripping one down on his 405 which has the same turbo. But as mentioned above it could be a csov problem

Going over 2600rpm then ‘bong’ is a symptom of the CSOV being stuck. Exactly the same happened to mine, stopped, lock the car, come back in a minute & she’s fine……until the next ‘boot’.
Indie stripped the CSOV (full of oil) and lubricated the shaft & alls well. Worth a look at? 2012 Orkney Grey Westminster 4.4TDV8 with Ivory interior.........nice!
BMW R1200GS
Alfa Romeo Giulietta
Just one Montesa now, 349 White Wonder
Austin A40 Farina MK2
1975 Morris Marina 1.8TC

If the tiny vacuum pipe that actuates the rod is loose, or off, it will give same symptom. It’s fed down the rear of the coolant radiator.