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Turbo Boost Issue


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#1 teamonkey

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Posted 30 June 2020 - 09:34 AM

Hi all,

A week ago I had a turbo boost failure while cruising along at 50-60mph. The turbo itself was replaced 26,000 miles ago and has not been driven hard - I rarely take it beyond 2,500 revs.

Took it to the local garage for a diagnosis and their opinion was that the N75 valve is faulty - sometimes called an EGR pressure convertor or boost solenoid.

Can anyone confirm this from their own experience ?

 

I know the EGR itself is filthy and the garage also recommended having the turbo manifold cleaned.

I realise some people like to completely replace/discard the EGR.

 

Any thoughts/examples would be most welcome and appreciated.

 

I'm just off to buy a new N75 from GSF for £36.




#2 adam-

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Posted 30 June 2020 - 09:43 AM

Took it to the local garage for a diagnosis and their opinion was that the N75 valve is faulty - sometimes called an EGR pressure convertor or boost solenoid.

 

I don't like that.  Garages shouldn't have opinions, they should know.  How did the turbo fail?


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#3 northpole

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Posted 30 June 2020 - 10:17 AM

I agree with adam- they should know... the thing is there are 3 valves if you still have the oem setup... n18, n249, n75
N75 = turbo
N249 = egr
N18 = egr return to vacuum reservoir
SO they should diagnose it to what the hell is going on... it could also be a simple vacuum pipe leak or a stuck vnt if they didn't tell you what fault code it was and just replacing parts for the hell of it isn't the way i would want to deal with it... So if they diagnosed it they should've given you a printout of the fault-codes they found. and if they did lookup the fault-code yourself before committing to buying anything.

#4 Bhavick

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Posted 30 June 2020 - 04:38 PM

Am no expert here but if you've got a VCDS cable it might be worth hooking it up to your car to scan it for any faults.



#5 teamonkey

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Posted 01 July 2020 - 09:19 AM

Thanks for the replies.

 

The turbo boost failed while driving by simply not producing its usual boost as felt via the pedal.

They diagnosed the fault via code-reader (which I don't possess) and testing so checked vacuum pipes, etc.

Stuck VNT ?

They didn't supply me with the code which I will now get and investigate further.

 

Cheers all !



#6 northpole

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Posted 01 July 2020 - 09:51 AM

yeah you got a variable turbo means it adjust itself to spool up faster and for longer so basically it is a combination of a small and a bigger turbo all in one...  the VNT mechanism is what does the trick... long story short the reason why we all block the EGR's is because they are the main reason for the VNT mechanism to get stuck, not weird if you think about it... exhaust gasses ( and with that soot particles, actually it's carbon particles, the black stuff that flies out of the rear back-box) get's partly put back into the engine... this and the crank-ventilation ( hot air with oil mist) not only saps away power but dirties up the intake and after a few years of driving it creates a buildup of a tar like gummy substance... this is what cause the intake and turbo's VNT mechanism to get  stuck... ( and the head also get's a good old dose of dirty gummy tar buildup too... now back to why we reacted like that... if you know the above than you can easily see why the vacuum operated valves (n75, n249 and n18) could easily be mistaken as the problem while there is something else that is the culprit.

 

also next-time you have them diagnose the car always ask for the fault codes and a printout of the results... than go home and check it either on here or use google to check the codes and find what it means and a possible solution. 

 

yes they told you the intake needs cleaning... they are probably right

yes the egr is filthy so it will need cleaning ( or even better clean and block it so you never have to clean it again) 

yes the VNT mechanism is probably stuck ( and probably the cause of the problem) - yes it needs cleaning

yes it might be a fault N75 valve... but the chances of that are slim, but can't be ruled out without proper diagnostics 

 

also just replacing parts to sort out a problem will get expensive really quick! so find the source of the problem and sort it out. 



#7 teamonkey

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Posted 01 July 2020 - 11:05 AM

So it could be just a coked up EGR and stuck VNT mechanism then ?

They said they diagnosed the N75 with a code reader - surely this is proper diagnostics ?

 

How is the VNT usually cleaned and time/cost ?

Garage reckons 2 hours to remove/clean/replace the EGR and turbo manifold.

 

I took it to the local garage in order to find the source of the issue - did consider taking it to VW instead for this but since they charge approx £110 an hour labour and as the local mechanic has an A3 and I regularly use them they seemed like a decent bet. However, we all know what tradespeople are like - having spoken to many mechanics over the years it is clear that sometimes opinions and diagnostics vary.

 

As usual, the good old Haynes manual uses different phrases for the same parts.

Don't suppose anyone's got photos of the n75, n249 and n18 valves for an ASZ ? (checked ebay).

 

I'm going back to the garage.



#8 northpole

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Posted 01 July 2020 - 11:48 AM

proper diagnostics? well could be but i would only except that if they would show me the faultcode and print it out... 

 

it is easy to see  the N75 has one long vacuum pipe going down towards the turbo they are all mounted in sight on the bulkhead you can't miss it ... that is the one you'll be needing if it is gone...  but 9 out of 10 times it is fine, and it's either a leaking pipe, or the VNT mechanism is stuck...

 

removing the turbo manifold would take them about 2  hours yes that is correct.. cleaning it however... is another story they either do it the right way and take it apart and it'll take them a few more hours to built the car backup... that is without them taking the intake and egr/asv off to clean by the way...  

they might use a proffesional turbo cleaner from holts or any other brand

 

the first time i did it myself it took me a day to take it off clean it all and put it back on the car with power being back to normal...  



#9 teamonkey

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Posted 02 July 2020 - 01:29 PM

Been back to garage - they wiped the fault code without recording it and now not displaying anything...suggested I should take the car for a test drive (30-40 miles) to try to re-create the issue and the fault code.

Test drove car as suggested (first time driven more than a couple of miles since original issue) but boost seems ok if a little subdued like it was in the few weeks before the loss of power.

Boost is there but doesn't feel as punchy as when newly fitted. Easy to say that it's not "new" any more but as previously said, it's only covered 26,000 miles in 5 years.

Mainly tested between 1800-2600rpm in 3rd or a little more in 4th, and turbo whine can clearly be heard at lower speed/gear acceleration.

 

Been reading a good, detailed post on here on turbo issues and resolutions/cleaning.

https://uk-mkivs.net...boost-problems/

 

Found the N75, thanks.

 

Mechanic reckons on cleaning the EGR with Mr. Muscle !



#10 adam-

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Posted 02 July 2020 - 01:37 PM

Log req/act and N75 DC and this will be solved very quickly. :) 


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#11 teamonkey

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Posted 02 July 2020 - 02:05 PM

Log req/act and N75 DC and this will be solved very quickly.

 

Er, pardon my ignorance - what does this mean ?



#12 teamonkey

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Posted 02 July 2020 - 02:07 PM

Hi all,

A week ago I had a turbo boost failure while cruising along at 50-60mph. The turbo itself was replaced 26,000 miles ago and has not been driven hard - I rarely take it beyond 2,500 revs.

Took it to the local garage for a diagnosis and their opinion was that the N75 valve is faulty - sometimes called an EGR pressure convertor or boost solenoid.

Can anyone confirm this from their own experience ?

 

I know the EGR itself is filthy and the garage also recommended having the turbo manifold cleaned.

I realise some people like to completely replace/discard the EGR.

 

Any thoughts/examples would be most welcome and appreciated.

 

I'm just off to buy a new N75 from GSF for £36.

 

 

Log req/act and N75 DC and this will be solved very quickly.

 

Er, pardon my ignorance - what does this mean ?

Log the requested/actual !



#13 adam-

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Posted 02 July 2020 - 05:47 PM

VCDS will be able to log what the ECU is requesting and what it's actually seeing.  The N75 will show us if it's controlling it, or attempting to.  


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#14 superchickenn

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Posted 03 July 2020 - 07:44 AM

just my opinion but clean the turbo with Mr Muscle, delete out EGR and delete N18 and N249, complete a vac simplification, see how you get on.. all stuff that can be done at home at not much cost. 

 

My ASZ is now on 270k on original turbo, driven hard most days.

 

You mentioned above not revving over 2600 rpm.. i find the PD's need a good blast to clear them out. 


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#15 northpole

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Posted 03 July 2020 - 07:46 AM

Mechanic reckons on cleaning the EGR with Mr. Muscle !

 

Look it up it's common practise... the thing that does the trick is the LYE and the foam as it clings to the sides for longer thus actually breaking down the build up... but if you don't fancy that and you got a gas-torch(that gives you a nice hot flame)  you can use fire to burn it off... basically it'll burn all the gummy buildup and leave you with just dry soot that you can than easily tap out or wash away with water...  the problem with the latter is it could crack the egr/asv and it might deform the ASV plate ( thing that looks like a throttle) so i suggest you do as they say... it's just a few bolts and removal of the intake pipe and you have the thing off, you can even re-use the gasket... 

but if you are using the ovencleaner to clean it out make sure every 30 minutes you rinse the stuff off with hot water, and re-apply the ovencleaner (keep doing that) until it's clean. 







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