Turbo knackered?

Hi guys.

Just fitted a 200TDi to a friend's Defender from a 2.5N/A. Engine conversion is all done and the engine seems to run sweet on the spot. Took it out for a drive and to start with it boosts very nicely, you can hear the turbo spooling up and it feels much nicer than the old N/A. Only problem is once the revs hit what I expect is around 2500rpm the car really noticeably backs off. This is any gear, and if you back off the throttle and go back on with the revs lower, it boosts as normal again up until higher revs.

The engine has been sitting for a while, so I discovered the wastegate actuator was seized shut, but I've now freed this up, but it's still the same. I've also checked the boost pipe to the fuel pump which doesn't seem to have any breaks in it, likewise the diaphragm in the pump is free too.

The turbo does have a little play in it, but not more than I've seen before on a used (but still working) turbo.

I can only conclude that the turbo is knackered and I'll replace it for a good used one, but my only concern is that it boosts very well upto a point, and every other car I've driven with a knackered turbo is pretty much dead on it's arse right from the off.

So is the turbo knackered, or are there any other ideas of things I can check before swapping it?

check if any of the pipework from turbo to inlet manifold is holed or clips are on tight so your not leaking boost at higher revs

We're using a new silicone intercooler hose set, which I can't see any splits on, and it all fits quite well, all tight at the joins etc.

Just a thought I've had though, which is something I can't physically be able to see out on the road is if the hoses to the turbo inlet are collapsing under higher load restricting the turbo. The boost hoses are all new and good, but the low pressure feed hose from airbox to turbo is just a scavenged bit of available hose that's softer.

I might take the inlet hose completely off tomorrow and take it for a quick spin to see if that's the issue. If it still happens, I know it can't be a restriction or soft hose on the low pressure pipework.

Almost certainly not the turbo either a fuel or air problem, rough guide if the turbo alloy vanes are not touching the housing its good to go.