Turbo boost issues

[Pops70]

OMG ..... I don't know what to check next.
The other day my D40 decided to loose power. Checked the boost via ODB2 and only had about 1 - 2 psi.
Took the vacuum boost solenoid out, cleaned it as good as I could and got a little more boost.
So clearly it's something to do with the vacuum not opening the actuator.
Just bought a new solenoid and installed it. No change. Bought vacuum hoses and exchanges all of the involved ones right the way to the side of the oil filter. No change at first, but after limping home, it got a little better. Boost ist at about max 5.5 psi. Still far from the normal 20 psi.
Connected the vacuum hose directly to the actuator and did a quick sprint down the road with 20 psi and power like a new car.
Now we all know that the vacuum hose is not supposed to be connected directly to the actuator.
On the solenoid got vac connected to vacuum, out to the actuator and atm to the third hose in the atmospheric side.

There are no fault codes by the way.

Has anyone got an idea what else I have missed?

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[Old.Tony]

Hi Pops, sorry I haven't gotten to this one sooner, we've got sketchy internet in Tibooburra at the moment and will be the same for the next couple of days. Looking forward to being east of Cobar for some decent internet!

You've replaced all the vac hoses with no change, but when you omit the BCS by attaching the primary vac hose to the actuator it works? That sounds like the BCS is faulty. If the BCS has been replaced, then it's the electrical connection to the BCS that's at fault. Check that cable, make sure there's no muck in it and try again. Your problem can't be anywhere else.

You CAN connect the vac hose directly to the turbocharger but you will get full boost at all times and there's a very good chance that you'll overboost (this will trigger limp mode) or even pop the manifold hose off (that's experience talking!).

If cleaning the electrical connection doesn't work, you can do away with the electrical control altogether (like I did) and get either a Tilix valve (like I did) or a Dawes valve. These use a spring to control how much vacuum is allowed through to the turbocharger actuator and although mine is now probably a little less peaky when it comes to power, I've not had a single problem with it in ages.

I am going to play with the needle valve in my Tilix valve - I think it needs to be opened a little, to allow more boost through at low-to-mid revs.