Variable Vane Turbo help please

Anyone an expert on variable vane turbos?
As fitted to my PD130

I have been aware for some time of people having problems with variable vane turbos sticking on petrol engines but hadn't really heard of it on diesels until now.

My PD130 won't go properly. Really flat until about 2,500 rpm, picks up briefly then goes into to limp mode. As noted in the deisel section a couple of people have plugged diagnostics into it but the current suggestion, including the diagnosis by the Seat dealer yesterday is that the variable vane turbo is sticking as they have measured it overboosting by about 25% and this then causesit to go into limp mode

The actuator lever on the back of the turbo appears to me to move freely by hand and the vacuum activated actuator certainly operates with the engine at idle.

If the turbo really is sticking, to be overboosting higher up the engine rev range I am presuming that the vanes are stuck in a postion relating to low engine speeds, so causing the excess pressure when the turbo spins faster. However, if it is stuck in low engine speed setting, why does it behave as though there is no turbo boost at lower engine speeds?

To me it is a contradiction for the turbo to be stuck in a maximum boost position yet not boost any longer at low revs. I would like to understand how this scenario can exist before paying out for a rebuilt turbo incase it's really something completely different that's causing the loss of power.

I have also tried running the car with the actuator vacuum pipe disconnected from the N75 valve but cannot feel any difference i the way that the car runsother than itmay be allowing me to rev it forlonger in the lower gears before it goes into limp mode. It will rev past 4,000rpm in first and second but under load in third it cuts out at arund 3,000rpm

Help!

 

Thanks for the links
Veedubs up in the Noth East have suggested unbolting the exhaust and spraying Mr Muscle in from that side
I'm also wondering about blanking the EGR if the car ever runs properly again

 

Bump!
Well I have not got the turbo off the car but have been laid underneath.
Have unbolted the actuator so that i can feel how stiff the arm for the variable vanes is and its absolutely free!
Easily clacks backwards and forwards between the external adjuster limit screw and whatever mechanical limit exists inside the turbo
I'm curious that it feels so free though?
There is no resistance at all, just really easy and slack backwards and forwards
Is this to be expected?
Is any internal resistance to be expected?
Any varaiable vane turbo experts out there?
Help please!

 

If it's overboosting which it is then either the vanes are sticking or the actuator is broken and isnt opening the vanes or the N75 valve is sticking open allowing overboost by diverting air from the actuator.

Unplugging the pressure pipe to the actuator will just make it overboost.

If the actuator rod moves freely then the vanes arnt sticking, therfore i suspect the actuator to be causing the problem or the N75 valve.

Check the actuator feed pipe carefully for damage or air leaks.

 

take the turbo out and check the vanes...only way to know for sure.
ring that opened and closes the vanes does not need much gunk
to stop it.
nothing sprayed in there is going to work, as you have to really scrape the carbon off, plus if it hase been stuck in the same position
it will need thorough strip and clean,

 

Pinched from Caddyforum, hope its of help.
Courtesy of Flyspeck.
http://www.vwcaddy.com/showthread.php?t=51079

 

worth a try ...bit harder if the lump is the right way round, ie golf..
my vnt mech was corroded too as well as carbon and had to chissle it off

 

Yep, as above, stripped one today from an octavia, carbon build up either side of the vanes causes them to stick then over boost. Limp mode happens next. Only way to remedy is strip and clean....Carefully!! New one from stealers is approx 699 + vat. No repair kit available.

 

Doesn't sound like sticky vanes if the actuator arm is free...

I'd go with investigating the air leak/n75 first

 

the actuator should be able to move with a suck on the vacuum pipe...
you could still move it before i cleaned it...not easily though.
after wards was a nice light movement

 

Yep again i agree. Actuator moved ok but once stripped cleaned and re-assembled moved alot better. If you have access to Vag-com you'll be able to see when the vanes stick and cause over boost. There is a 'Desired' boost pressure and an 'actual'. The graph shows that limp mode happens when it overboosts for too long. The one i did had an ASV engine and shouldn't be boosting over 2040 mbar (2 bar) but was boosting over 2500 mbar.
OBVIOUSLY BASICS SHOULD BE CHECKED FIRST BEFORE ATTEMPTING TO DO THIS!

 

Vacuum on the actuator pulls the vanes into maximum boost position, so leaving it unplugged keeps it at minimum boost. Leaving it off isn't making any difference. The engine is still gutless below 2,300 rpm then boosts and goes into limp mode when held for long above that speed.

Knowing that the actuator and arm were moving freely I had reached the conclusion that the vanes may indeed have stuck and had heard of instances of the arm failing/snapping internally.

Tonight I have run the car with the actuator unbolted and the variable vane arm locked into maximum boost position. Low speed running is transformed with the car again pulling hard from 1,500 rpm so i now doubt any mechanical fault in the turbo despite the local Seat dealer having concluded that it needed a new turbo.

 

The actuator clearly gets drawn to full limit with the engine at idle and sucking down the pipe there is no loss of vacuum from a leak.

So I am back to suspecting some sort of control problem and would be thinking N75 valve pack if it weren't for the fact that the car behaved exactly the same way when tested with a used N75 (which admitedly could have been faulty too)

 

For anyone interested, my car appears to be fixed by a new boost pressure sensor

 

did you ever get it plugged in , what were the faults?

 

Yes was plugged in three times
Was initially diagnosed as N75
Then as "overboosting"
Then to Seat dealer who also recorded overboosting and diagnosed the turbo
Trying the boost pressure sensor seemed a good option, clearly it was giving the ECU duff readings

 

My s4 complained of overboost when it had two massive boost leaks. Are you def air tight?

 

click here for a guide on how to de-coke your vnt without removal

 

Or, use the proper stuff..

Or, use the proper stuff:

http://www.spdiagnostics.com/index.php/products/workshop/revive-turbo-cleaner

 

Any ideas where we can buy this?