Turbo lag low down

[johnnyroper]

Recently I have noticed a bit of turbo lag low down rev range developing,gets to about 1800 rpm and it starts boosting normally.
No faults logged in system. I seem to remember it started boosting about 1250rpm before.

About 6k ago when doing head the vnt was cleaned and freed up I can still move actuator by hand ok,the actuator pulls down when engine idling and returns when switching off.
All filters etc are new.

I am thinking poss n75 issue but reluctant to shell out Ã,£100ish for a new one just in case my hunch is wrong.
Is there anyway to test it or anyone got any other clues as to likely cause before I bite bullet and get one?
115bhp auy engine with manual transmission of that makes any difference.

[FGTDI]

Not sure if this will be of any help?
http://uk-mkivs.net/topic/50753-sticking-vnt-mechanism/

[mike wilson]

Note the posts in the link above from #25 onwards.  Some people have modified their turbo housing to allow easier access to the vane mechanism.

[johnnyroper]

Cheers for the replies.
It just so happens to be a recon turbo fitted 18 months ago so will plot a run on vcds and see what's happening.
Probably will mr muscle it again and check adjust the rod as per the post instructions.
Anyone know the part number of n75 as mine has got identical n75 and egr solenoid fitted,I am sure they look same but are actually slightly different internally?

[johnnyroper]

Did a block 11 test today idle rises to 1400 DC goes up and down and actuator moves as it should.

Ran a block 11 test run log from 1200rpm to 4000rpm WOT in 3rd can see boost slow to build low down and then comes in at about 1850rpm. Then at about 3600 DC reaches 94% and triggers over boost and limp mode. Will have to try a mr muscle clean of vnt first and if that works strip and clean properly when time allows. Failing that will need to lengthen actuator rod a turn at a time see if I can get it to 80% DC at 4000rpm.
Got to say if anyone has got boost issues the thread linked above is excellent for diagnosing and resolving them.

[johnnyroper]

Took advantage of the nice weather and had a tinker with turbo I took actuator off and found the vnt was a bit sticky so have it some mr muscle. Took for another spin and it was improved now got low down boost and no limp higher up but it was still reaching 88% DC.
Gave the rod about half a turn and made longer.
Boosting well and getting 81% at 4K now.

It's all very fiddly to do as space is restricted from up top so no pictures taken.

[Mirez]

Ahh good work, those figures sound good.

I never understand how they go out though, its a metal bar connected to a solid mechanism so nothing to wear as such that could cause it to be out so much!

[johnnyroper]

Only thing I can think is over time the diaphragm in actuator wears causing it to lose accuracy or the VNT vanes cause it as they wear?
Very odd though how it can change so much.