Hi, I have 2008 Focus 1.6 tdci hoping the kind people on this forum can answer a question for me, I’d like to know if the vacuum supplied to the turbo actuator increases or decreases the turbo spool? 
Basically I’ve got a problem with getting too much boost pressure and think I’m narrowing down the reason to the vacuum but knowing the answer will maybe help diagnose further I.E. if not enough vacuum would produce overboost then I can consider some kind of leak or possibly the vacuum solenoid, if too much vacuum would cause overboost then at least I can rule out a leak somewhere.

thanks for any help I may receive.

AFAIK, there is either a wastegate or variable vane design but in any case, why not disconnect the actuator pipe and see if the fault changes.
If it doesn't then the actuator system needs looking at (can you see it working)?
Test the actuator and vacuum connections with a vacuum pump if nothing found then the control solenoid then the wiring.
I'm saying this as an initial thought without any real knowledge of that vehicle and you don't give the exact fault codes or how they were obtained (Forscan or ?)

Hopefully someone else may come along and answer your specific question but in any case, Welcome!

Wastegate on 90ps.  VNT on 110ps.

Thanks Shearers for your help, it is a variable vane turbo and can confirm when engine starts that the actuator arm retracts under vacuum still don’t know if this is effectively turbo on or off but yes I could pull the vacuum pipe and see what it does to the pressure readings using forscan to probably get my answer, I could do with some pliers to do this and currently in the middle of nowhere without tools 😁 so still would appreciate the info if someone is familiar with the turbo on 2008 1.6tdci focus

Just pull the vac pipe off.  If you've still got boost, then vacuum opens the vanes.  If you haven't got boost, then vacuum closes the vanes.

I owned and worked on plenty of these but can't remember which way round it is now unfortunately.  You'd expect a failsafe default to vanes open but I've got a feeling the vanes are naturally closed on these.

Thanks, yea I’ll have a go doing that tomorrow, I did google about this and though couldn’t find anything too definitive I think you’re right, my best guess is that the turbo is on without vacuum which is kind of surprising if so given like you say you’d think fail safe would be other way round. 

Okay so managed to whip the vacuum hose off the actuator and getting no boost so vacuum=boost. I’m getting too much boost is it likely the vacuum solenoid could be faulty? I’m really out of any other for this overboost problem, it’s definitely correct readings as I’ve had two different MAP sensors on and the turbo and actuator have also been replaced the overboost has been same throughout. Also if anyone has any other thoughts other than a faulty vacuum solenoid? Thanks 

So, to confirm, with the vacuum pipe disconnected, you get no boost (the actuator doesn't move?)
With the vacuum pipe connected you get the overboost fault?
To me, that says the actuator is being incorrectly supplied likely with full (or excessive) vacuum.
If you don't have a way of measuring that, the solenoid actuator is the next place to go.
Test it for resistance (there should be some, perhaps 12 Ohms  as about 1 Amp would seem reasonable???)
If there's infinite resistance, it's open circuit and has definitely failed.
If you can suck from the inlet to outlet i.e. the actuator is always receiving full vacuum then that will give you the overboost and it's stuck in that position.

When connected across battery, it should click or show a slight spark meaning it is trying to work and the vacuum flow between the two relevant ports should change to blocked or open as the current is on and off:
https://www.youtube.com/watch?v=6RWS_kogk9c&t=11s

This one has a commentary and says 28-30 Ohms for that specific type:
https://www.youtube.com/watch?v=SKtezjfO-W8

But he's using pressure rather than vacuum and I'd either use Mityvac or just blow through as a basic test.

This shows what's inside:
https://www.youtube.com/watch?v=dkPuEmwP4oQ

This one shows air filter (yet another failure point):
https://www.youtube.com/watch?v=3Mty5n9UpF4

 

 

Wow thanks for the super detailed help, regarding first paragraph yes that is all correct. Regarding the rest that is really helpful on how to check the solenoid etc, I’m actually on a road trip round Europe at the moment so none of the checks are going to be easy for me to do but my missus is flying out to me on 3rd of August, I’m thinking I might just order a solenoid and get her to bring it out to me. So that’s probably it for this post for a while, thanks so much for all the responses you’ve all been very helpful.

I don't leave home without a multimeter 😉.

Hope you can get it sorted, do let us know and enjoy your holiday!

Thank you and yes will update once fitted 🙂