adjusting the length of the VNT rod - 2.5 TDI

audi2.5tdi

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ive been doing some reading about the length of the control rod for the VNT mechanism on the turbo, the turbo is a GT2052V (701s)

i found a thread on another forum about how to check if its correctly adjusted, 2000-4000 rpm in 4th the duty cycle of the N75 valve should be between 70-80% @4000 rpm

if its below 70% @4000 rpm the rod length should be shortened and if its above 80% @ 4000 rpm the rod should be lengthened

i ran a log in VCDS and accelerated from 2000-4000 in 4th and the duty cycle @4000 rpm was only 58.8%

so i shortened the rod and did the same test

now @ 4000rpm its only 35.5%

which is the opposite of what i was expecting to see!?

this is the tread i got the info from

http://uk-mkivs.net/topic/34834-vnt-tdi-turbo-how-to-adjust-actuator-cure-boost-problems/


and this is the paragraph about adjusting the rod

"How to adjust the VNT rod length
When these turbos are new straight from Garrett, the rod length and stop screws are setup professionally in accordance with their specifications. since they do not publish these specifications alot of re built, re manufactured, re furbished turbos do not have them properly set up. This includes so called "Garrett approved turbo re-builders" most of the time they will just leave them as standard and expect them to work, and they will work most of the time but obviously there is going to be times when they don't. And because the hybrid turbos are different specifications, the rod length and stop screw specifications from Garrett will no longer apply. this means the turbo must be set up either on a flow bench or on the car.
Adjusting the rod length is necessary if you are getting errattic boost problems, if your duty cycle is above 80% at 4,000rpm then it needs made longer, and if your duty cycle is below 70% at 4,000rpm it needs made shorter. between 70-80% is ok, the closer to 80% the better.
How I do it is remove the TIP and get at it from above, it is possible to do it from below but theres limited space down there too, I prefer the top way.
so once you have removed the tip, you will be able to see this-"



is the 70-80% duty cycle what i should be aiming at at 4k rpm? should i try lengthening the rod past the original point and see if it goes the other way?

is there another way of doing/checking this?
 
right, i think it should be the other way, @4000 rpm it needs to be down near the 30% mark

ive wound the rod in a bit more (shortened) and its now down to just over 30% @ 4000rpm

its much more responsive low and mid range and still pulls cleanly all the way through to 4500rpm

seems to pull from lower down now too, it has instant pick up from about 1500rpm and really comes alive at 1800rpm+

the car has the following done to it;
1999 2.5 TDI Quattro AFB engine (150bhp)
2003 AKE turbo (701s)
2003 AKE injectors
EGR delete
Cats gutted
rear box gutted
Steenbauer tuning box

all belts etc changed 10k miles ago, pump timing done with VCDS
 
You should never have to alter the rod length on the actuator. Usually there is some other undelying issue that is causing a problem, fuel supply, boost leak, MAF sensor , MAP sensor etc.
Unless the turbo has been fiddled with or it's a recon that hasn't been set up properly.

The link you pasted is for the EDC15 ECU on the PD engines and I think you have found out that on a lot of engines it actually works the other way around.The mark space duty cycle is seen the other way around.

The acid test is to see what the duty cycle is at idle, this will be pulling in the VNT rod to the maximum to give the most low down boost on a PD it's something like 15-20% , I suspect on yours it's more like 80% as the boost increases the duty cycle changes.
It sounds to me like you have it set right now .
If you ever need to know anything about these engines Chris Adams @adamss24 is the man to speak too.

Karl.
 
85.2 % at idle, should that be less than that, 80%?

in which case the stop screw should be wound in to open the vanes slightly at idle?
 
Well that proves it does work backwards and 85% sounds about right. i wouldn't touch the stop screw if it's running alright.

Karl.
 
excellent, saves taking the vacuum unit off to try and loosen the lock nut

i would suggest that it is a rebuilt turbo that wasnt set up properly as its covered in marking fluid on the lock nut for the stop screw and actuator rod

its defiantly more responsive now
 
If you have a read through here I did some messing about a while back with actuator rods and stops that may help you.

The UK-MKIVs site is for 1.9s, where the measuring value is reversed, look at my graphs and you can see what is going on.
 
Hello

If you need correctly adjust the VNT, quite helpful is this movie:




If I know what is your turbocharger OEM No, I will give you data concerning pressure actuator to set precisely VNT in your Audi.