Offroad-Express

Have a boost issue that hopefully someone can shed some light on.
Had a scarles turbo fitted 9mths ago, no intercooler, ran well, with max boost of 10 psi, no probs at all since fitted.
Week ago using it for first time since Christmas (not a daily driver) on club trip discovered it was showing no boost on gauge and was definitely not feeling or sounding like turbo working, ie at full revs 0psi. was like this for the whole day .
This week, pulled inlet off- to check turbo was spinning - all good there. thought maybe internal waste gate stuck open, so disconnected actuator, moved it a few times and reconnected, it appears that the actuator rod in rest position is holding gate in closed position. Disconnected boost line to actuator, fed air in and actuator still moves out and boost gauge showed the pressure. Reconnected and took for drive.
Suddenly ive got boost again, but now its 6psi max instead of the original 10psi.
thought ok- maybe actuator prob, so Disconnected actuator rod off wastegate spindle, wired the spindle in the shut position, took for drive, this time, its barely does 3psi. Put actuator rod back on, again its drives well again, rev well etc, but only 6psi max, note boost quickly to 4 psi just off idle like it was when new.
Plan to drop in to a turbo specialist on Monday night, but maybe someone on here can guide me on the issue.
Ive never played with diesel turbos before so im unsure if im missing an obvious issue.

Maybe the diaphram atop the pump, turbo can only create boost if the extra fuel load is there to match it.

some thing stupid but check your air intake & filter is clear

You could also try disconnecting wastegate and going for a drive to see if it creates more than 6psi to eliminate a turbo problem.

I would make sure you don't have a split intercooler joiner , restricted intake or exhaust or blown/leaking exhaust gaskets , is it a non turbo pump ? make sure there is no fuel restrictions , blocked filter guaze in feed banjo etc , Possible a fexed turbo also