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Discussion Starter · #1 ·
One of the girls at work has a T.D.I 110 and when over taking her turbo cuts out resulting in lack of power. She then has to stop & restart the car to get the turbo working again. It's been into VW last week and they replaced the air mass meter.

Anyone any ideas what's causing it?
 

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I would go with the turbo on this one, either that or the 'N75' valve.

What happens is the ECU recognises the turbo is overboosting and it shuts it down by holding the wastegate open permanently until and ign off/on has been done.

It is 'almost' common now that the wastegates on higher mileage TDI get sticky and on initial full throttle in higher gears its doesnt move quick enough to maintain a steady boost and you get a pressure surge of up to .5 bar more than is wanted, and the only fix is to repace the turbo unless you know a 'turbo specialist'.

The reason it could be the well talked about 'N75' valve is that this is the valve which the ECU uses to control the wastegate which determins boost pressure, and if it is faulty it could be allowing the turbo to overboost by mistake.

There was a big thread about it a couple or three months ago which pretty much went along the same lines.
 

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I was under the impression a diesel had neither an N75 or a DV??!!

I agree with NikB - Deffo a split hose! The symptoms you describe Mart4875 are exactly what my Anni TDI had and that was a split intercooler hose
 

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Royster they dont have a dump valve but they do have a wastegate, they are 2 completely different things.

On a petrol when you lift of the throttle the butterfly closes over and unless the excess air was dumped the turbo would effectivly stall due to there being no more air getting in.

Since diesels dont have a butterfly to close off the intake they dont need to dump the air, it simply blows through the engine.

The wastegate is there for the pressure control under all occasions, to prevent overboost being high priority on any turbo car.

Anyway, would the hose reset by turning the ignition off/on ?
 

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Only a 90bhp tdi has a wastegate(which I think changed near the end of its life), the 110,115,130 and 150 don't have one. I do believe they have N75's though, still have to control the boost
 

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I seem to remember a post about 2 months ago, with this in mind. He removed the turbo and cleaned the actuator, it gets coked up, being the diesel type. It sorted it, worth a search.
 

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I think your going to find its the wastegate on the turbo mate. Whatever you do, dont get VW to diagnose it, it cost me ?260 and they had the car 2days.

As far as i am aware you have to replace the Turbo, VW qouted me ?1300, so I went to a turbo specialist and they did me a re-con unit for ?250, I then paid a garage to fit it, think it was only a 2hour job so quids in on the VW qoute.
 

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Weeloon - All but the 90bhps do not use a wastegate, they are VNT turbos, it uses an actuator just like the wastegate turbos do but NO gas is bypassed, the vanes change angle to stop from overboosting.
 

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Quote: posted by weeloon on 23/01/2005 12:52:16Royster they dont have a dump valve but they do have a wastegate, they are 2 completely different things.

I know mate I've had a 1.8T[;)]

But when I asked this question about a year ago (and someone else did) the general concensus was the "N75" was missing from the TDI certainly the name "N75"[:p]
 

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For those reading this expecting the wastegate to be at fault, read this http://tdiclub.com/TDIFAQ/TDiFAQ-1.html#g

quote, 'To improve performance in "off-design" conditions, the A4 engines (and the A3 110hp engines) use a variable-geometry Garret VNT15 turbocharger. There is no wastegate, and all of the engine exhaust passes through the turbine all the time.'

The same applies to the other tdi's that use VNT17's
 

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Discussion Starter · #14 ·
Thanks for the replys guy. She's had it back in @ VWs twice now and they found a split hose first time which they replaced but then low and behold it's still doing it but not when the techy drove it.
 

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You should get a vag-com and check actual vs requested boost. If the boost keeps rising with revs a lot higher then requested, your VNT turbo might have a case of sticking variable vanes. This might also explain why you had split a hose (too much boost).

This could be avoided by giving the car some lead foot and high revs from time to time so the vanes keep moving.
 

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mine is doing this at the moment.although only about 75mph in 5th. they had it in. changed a valve. still the same. It is now booked in on the 7th feb for three days to do tests on the turbo. If it wasn't under warranty i wouldn't have it near the dealers.Lets hope they fix it this time or i'll be having words. A search on google shows pictures of the turbo and a common fault is it sooting up and causing the actuator to stick. It is only controlled by a vacuum pipe.
 

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farmer - the valve they changed will be the one that controls this actuator, the valve is commonly known as N75 and it controls the wastegate actuator (and as aiden says on the variable vane type it controls the butterfly actuator, which is the same as a wastegate when it comes to overboost and is not as widespread as he thinks especialy on earlier models)but anyway its the rod for this actuator that sticks/moves to slow and allows excess overboost, and as its an internal part of the turbo it either needs a new turbo or a specialist to sort it, and not all can be sorted depending on how long its been running damaged for.
 

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Discussion Starter · #19 ·
Quote: posted by farmer on 26/01/2005 18:45:27

mine is doing this at the moment.although only about 75mph in 5th. they had it in. changed a valve. still the same. It is now booked in on the 7th feb for three days to do tests on the turbo. If it wasn't under warranty i wouldn't have it near the dealers.Lets hope they fix it this time or i'll be having words. A search on google shows pictures of the turbo and a common fault is it sooting up and causing the actuator to stick. It is only controlled by a vacuum pipe.

Let us know the out come mate.
 
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