I'm confused, I know my VRS has it, but I seem to be getting conflicting opinions on how it works. I've watched these two videos on youtube and they seem to say the opposite thing!!

- Vanes open at low boost!!!

- Vanes open at high boost!!!

Now which is it??? Or am I just being thick here? On a VRS, should there be vacuum at the actuator on tick over???

Cheers

Rich

http://www.honeywell.com/sites/ts/tt/turbofactsbenifits_VNTworks.htm

Its less about "high and low boost" and more about it being more "willing" to boost faster with the vanes closed. If the vanes remained closed, the turbo would overboost massively and essentially self destruct. This is why the VNT vanes move open, to allow the boost to reach maximum sustained point in a controlled fashion.

So in essence it is closed for low boost, and open for high boost, but it is a little more complicated - it's something even I have only just learned about recently with my turbo rebuild.....

http://www.honeywell.com/sites/ts/tt/turbofactsbenifits_VNTworks.htm

Cheers, just re-watched the youtube videos, and I think I'm having a thick moment! They are both the same, I was reading turbo rpm as engine rpm, my mistake! Sorry.

So at tick over then, are the vanes wide open as no boost is required? In which case I assume it'd show no vacuum on the actuator pipe??? This is assuming the vanes are spring loaded to the open position(none or low boost) when turned off??? Sorry for all the questions, just trying to get my head round how this thing works, and sort out a few on going issues!

Cheers all.

It's all slowly sinking in(I think), I guess the turbo only has to spin so fast to create the correct boost, so additional exhaust gases(ie engine revving faster) are countered by opening the vanes to prevent it spinning too fast creating too much boost???? Am I on the right tracks here?

It's all slowly sinking in(I think), I guess the turbo only has to spin so fast to create the correct boost, so additional exhaust gases(ie engine revving faster) are countered by opening the vanes to prevent it spinning too fast creating too much boost???? Am I on the right tracks here?

Yup you got it. The VNT is simply there to reduce turbo lag. The N75 vacuum control lives inside the black vacuum box on the drivers inner wing near the windscreen end. This applies vacuum to the VNT actuator mounted on the actual turbo. The vanes are closed ( or more correctly positioned in the restrictive flow position) at light throttle. As boost demand increases, the N75 applies more vacuum, the vanes are opened progressively to control the boost.

The whole process is fairly complex, as there is exhaust gas flow rate, fueling, engine load, actual boost as measured by the absolute boost pressure sensor mounted on the inter-cooler, all used to calculate correct boost, without killing the turbo.

When the VNT sticks, it almost always sticks shut, and the car will over boost briefly, and then the ECU will slam into limp mode, to protect the turbo and engine. A good Italian tune up keeps the vanes clean(ish)

Yup you got it. The VNT is simply there to reduce turbo lag. The N75 vacuum control lives inside the black vacuum box on the drivers inner wing near the windscreen end. This applies vacuum to the VNT actuator mounted on the actual turbo. The vanes are closed ( or more correctly positioned in the restrictive flow position) at light throttle. As boost demand increases, the N75 applies more vacuum, the vanes are opened progressively to control the boost.

The whole process is fairly complex, as there is exhaust gas flow rate, fueling, engine load, actual boost as measured by the absolute boost pressure sensor mounted on the inter-cooler, all used to calculate correct boost, without killing the turbo.

When the VNT sticks, it almost always sticks shut, and the car will over boost briefly, and then the ECU will slam into limp mode, to protect the turbo and engine. A good Italian tune up keeps the vanes clean(ish)

That's what I'm thinking. Had limp home mode 4 times now, always under hard acceleration. cycle the ignition and it's fine again. Have replaced boost pipe seals, MAF sensor, checked vacuum lines but can't see anything wrong. Had error codes read and there are none. Have been underneath and unbolted the actuator and the VNT seems to move freely enough. Hoping to try swapping the VNT valve block for a friends at work, just to see if it makes a difference(he's a bit iffy that it might screw his car up too). Have read good things about Forte diesel cleaner so I've bought some of that(I'll try anything :-)) and then I'll get some Innotec turbo cleaner and try that! If that fails, I'm using it as one big massive bbq! :-)

Cheers

As the owner of a 1.9 TDi110, VNT faults are a subject close to my heart!

On the 110 (and the 90) the problem is normally that the nozzle sticks open, leading to over-boost, limp home mode, and leaving an overboost error code in the fault log. I can't remember the number, but if you put a code list into something like Word, and search for overboost and synonyms... (by synonyms, I include overboost, over-boost, over boost)

Cheers, but that's the weird thing, I am not getting any error codes!!! :S

Oh, another thing which I thought I'd mention, my car has the PD160 intake pipe. Had it on when I bought it, don't think it had been remapped though, as it felt no different to a friends standard car!!!

Edited 14 June, 201016 yr by jacko2111

Cheers, but that's the weird thing, I am not getting any error codes!!! :S

Oh, another thing which I thought I'd mention, my car has the PD160 intake pipe. Had it on when I bought it, don't think it had been remapped though, as it felt no different to a friends standard car!!!

Very strange. Limp mode should always throw out at least one code. Do you get a CEL light warning? Do you use VAGCOM or a simple OBD2 hand held scanner, the smaller scanners don't scan all the system modules, although they do scan the ECU for sure.

Very strange. Limp mode should always throw out at least one code. Do you get a CEL light warning? Do you use VAGCOM or a simple OBD2 hand held scanner, the smaller scanners don't scan all the system modules, although they do scan the ECU for sure.

Right, last night I went over the boost pipes and vacuum lines again, couldn't find any issues. So I took the turbo actually off(again) and moved the mechanism by hand, and now it does seem to be sticking towards the top of it's movement! So I spent a good 5-10 minutes moving the mechanism up and down till it felt a bit looser. Took it for a blast, and when I first accelerated I got a cloud of crap out the back(Hopefully loosened carbon). Up the bypass got it up to a decent speed then boost dropped again, but this time I have got the CEL light on. Anyway, will get this read and see what it says. Will probably try some of this http://www.innotecworld.com/c-1064-turbo-clean-set.aspx as it seems to get good reviews on varous Golf and Seat sites. If it ain't this, then I really haven't a clue! The annoying thing is I've only had the car 5 months, I bought it to replace an ageing and rusty MX5, as I was getting fed up with 28 mpg and having to weld it up all the time!!! Starting to regret buying the damn thing now!!! :(

Sorry, mean't to add, don't have VAG COM, but a friend with a small garage business has a scanner device that he uses, he reckons it should be compatible with it!!! :S

Edited 15 June, 201016 yr by jacko2111

OK, got my el-cheapo scanner today, took the car for a drive first after adding some Forte diesel cleaner tothe tank, then when I stopped after about 5 miles the CEL light went off! Anyway, did a scan and I have a 17965 code, positive boost pressure deviation(Over boost I think). So I'm hoping some Innotec put through the turbo will sort it!!! Aside form all this, I've also ordered some silicon vacuum hose to replace all the little pipes even though they appear fine! Cheers. Will let you all know the final outcome, thanks for the help!

There's a PDF with loads of pictures on how to strip down and clean the VNT over on the TDi Forum. I'll see if I can find a link.

Here you go

http://pics.tdiclub.com/data/500/Drivbiwire_VNT_repair_procedure_small.pdf