[Matt 130]

Hi,

Posted this in the engine forum, but was kindly suggested to post it here also:

Got a 2nd hand Y reg GT TDi (130) Yesterday, and it appears the Turbo sometimes cuts out at high revs and doesn't 'cut back in' until I restart the Engine.

Anyone have any idea as to the severity of this please...?!

I've just come off the phone with the sales man, he says it's a common fault and that it's the air filter(??) cutting the turbo out. Is he spinning me a yarn...?!

Thanks

 

[MRK IV]

Yes. Two things to check: MAF and your throttle body. Is it drive by wire?

 

[asgh4r]

i had exact same problem matie. it is something to do with an overboost. vag com will sort it. i was crapping it, thought my turbo went. lol. if you know anybody with vag com, they can sort it. i think a few people coming to the midlands meet will have vag com

 

[sssstew]

Quote: posted by MRK IV on 11/06/2004 19:10:17

Yes. Two things to check: MAF and your throttle body. Is it drive by wire?

diesels dont have throttles. But alas as the other post says its very likely to be an overboost problem leading to it going into limp mode, have a quick search for those key words and you will see some more info.

But usually a split intercooler pipe can lead to this, but vag com should confirm this.

 

[Matt 130]

Cheers to one and all for that, I'm taking it in for a quote on Wednesday, then I can tell the dodgy bloke I got it from, what VW say is wrong with it...

He's(and his mechanic is) adamant that it's some filter or other which he says are 175 quid...? Either way he's gonna put me a new one on?!

Unfortunately I don't know anyone with VAG COM, or anything about it for that matter...?! [:I]

 

[jackster1]

mine had same prob, just smacked my a++se for ?900 for new turbo to be sup/fitted, now i smack others a==rse on motorway, what a difference like a new car

 

[Stewart]

?175? They could mean the MAF (Mass AirFlow meter/sensor) this sits inline with the air filter, just behind it...

 

[Matt 130]

Quote: posted by jackster1 on 19/06/2004 17:58:55

mine had same prob, just smacked my a++se for ?900 for new turbo to be sup/fitted, now i smack others a==rse on motorway, what a difference like a new car

Indeed, I've taken it into a VW garage and it is the Turbo that's gone... ?1005 all in... I'm now in the process of arguing with the garage where I bought it, getting them to pay for it.

 

[sssstew]

chuffin hell! ?1k!! ouch! best of luck matey.

 

[A3TDI]

It`s not the turbo, same happend to me everyone i spoke to wanted to sell me a new turbo, it cost me ?12 to repair myself, for a few gaskets. it`s the variable veins on the turbo, they rotate in the manifold and after time a layer of rust inside the manifold jams up the smooth rotation causing overboost and cutting out the turbo. it wants stripping and cleaning and it will be as good as new. http://www.technologie-entwicklung.de/Gasturbines/VNT15-Turbo/vnt15-turbo.html will take you to a stripped turbo to look at.

 

[rhemingway]

guys this is exactly what happend to me a week or so ago. I thought it was probably MAF related.

THe people who have experienced this problem can you tell me how often it happened to you. So far my car has done it once, but I was hustling it which I dont often do. I assumed it had to be electronic / sensor related because it was fine after turning off and on the motor.

Surely it cant be a new turbo.......that must be the garage having a laugh.

Rich

 

[rhemingway]

guys this is exactly what happend to me a week or so ago. I thought it was probably MAF related.

THe people who have experienced this problem can you tell me how often it happened to you. So far my car has done it once, but I was hustling it which I dont often do. I assumed it had to be electronic / sensor related because it was fine after turning off and on the motor.

Surely it cant be a new turbo.......that must be the garage having a laugh.

Rich

 

[Milkfloat]

Get it on VAG-COM and see what codes are being thrown up. Th ecar is simply going into limp mode, which can be seen as a safe get you home mode.

 

[weeloon]

On your model of car I can only see it being an overboost fault, the fault code will probably read 'pressure regulation limit exeeded', what happens is the wastegate on the turbo goes a bit sticky meaning its movement is slowed down, when you boot the car the pressure is regulated by N75 operating the wastegate to a steady 2.1 bar but if the wastegate is slow to move the pressure can go up to 2.6 bar for maybe half a second or so and this can be long enough for the ecu to recognise the overboost and it then tells N75 to open the wastegate full time to prevent damage to anything (until the ignition is turned off and on again)

So you can get someone to adjust when the ecu recognises overboost via vag-com (which isnt a good idea as its sticking) or you get the problem fixed which is usualy a new turbo as the wastegate is built into it and only specialists should realy tamper with them.

Anyone reading this that has vag-com if you check measured values 11 block 2 and 3 in the engine they should read spec 2160 and actual (should be similar but can read up to 2590 is sticky) when on intitial full throttle, best seen using the scope view

 

[rhemingway]

I connected up vag-com and was doing a run down the motorway when it happened again, it went into limp mode. This time I got the code:

17965 - Charge Pressure Control: Positive Deviation

From searching threads I understand it could be:

Leaking intercooler hose

Leaking pipe from waste gate

MAF

Turbo variable guide vanes sticking (strip down and clean)

Turbo waste gate (new turbo needed)

Can anyone tell me from experiance which it is likely to be. I am going to try and find out if the maf is goosed this afternoon. Will post results soon.

Thanks for any help.

 

[weeloon]

rhemingway, did you read what I wrote ? Its written from experience

 

[rhemingway]

weeloon

thanks, i did read everything you wrote. You have been a big help. If you could let me know what you think of the graph below it would be very much appreciated, or any one else for that matter.

I did not get chance to do a 'proper'(ie 3rd gear full load etc) test so used the log from my last run. As I said, shortly after full rpm it went into limp mode. I would ideally like to know what anyone thinks of the MAF.

Any comments much appreciated.

here is the link to the .xls with the data (and graph)

http://www.baymotorcycles.com/richard/logmaf.xls

here is the graph. (CLICK TO ENLARGE)

 

[weeloon]

Its showing that the actual airflow is higher than the ecu wants which suggests its being forced in by the turbo right up until the ecu kicks in valve N75 and then its less than the ecu wants.

As yours is the 150tdi I would check your readings in block 11, it will give you actual and specified boost pressures, under full load yours should reach about 2630 (2.63 bar)but if the wastegate is sticking at all I have seen them at 2960 (2.96 bar)

 

[rhemingway]

thanks again for the informative reply. I will do a proper run next week (on holiday at the moment in Germany).

I now understand the purpose of the wastegate and it appears its easy to check its operation using vag-com as you mention.

one thing I am not sure about is why the actual airflow is so much higher than the requested. Why isnt the ecu activating the N75 sooner? and is this normal? I think that on the graph, when the MAF Actual flatens out completly was probably when it went into limp.

CHEERS.

 

[weeloon]

N75 is activated as soon as th ecu sees overboost, its the fact the wastegate is slow to move is the reason it overboosts so much