# The N75!



## KentishTT (Jun 28, 2007)

What does it do and how do I check it and what symptoms do you get when it's failing?

Just wondering b/c I have a bit of a flat spot until I get boost now (comes in around 3.5k rpm) and feels less linear than it used to, like it's tailing off. Boost is strong form 3.5k to around 4.5/5k rpm and then it feels a bit dithery.

No fault codes stored.

I had a new MAF from Wak last Dec so hope it's not that!

Wondered whether it's my "original" N75 failing?


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## KentishTT (Jun 28, 2007)

It would appear the N75 is a bit of a mystery - does nobody know what it does and what the symptoms of a failing valve are?

:?


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## KentishTT (Jun 28, 2007)

Uhhm. looks like I'll be the first here to uprate my N75


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## T3RBO (Dec 9, 2003)

The N75 valve is used to regulate the maximum turbo boost pressure, when the actual pressure at the intercooler reaches the command pressure (pressure demanded by the engine management ECU) the N75 valve starts to open which controls the waste gate in the turbo. This has the effect of diverting the exhaust gasses past the turbo reducing its effect and resultant charge pressure.

The N75 valve position can be read by VAG-COM in block 113


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## KentishTT (Jun 28, 2007)

Thanks very much for the info, I think I'm still on the original and I suspect it may not be working too well.

I'll check the readings with vagcom.

Thanks!

K


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## softalino (Feb 16, 2009)

Again sorry for my bad english.

I also suspect that my N75 is not working good anymore, so I made a log on the VAG COM where I monitor the commanded pressure and the pressure at the intercoorer. Further I looked at the N75 duty cycle and I compared the actual load against the spec. load. It looks like this:








It would be a good idea to compare this figures with some other TT's. I suspect that my N75 is not so good anymore because the actual load is smaler than the spec. load. (please correct if I am wrong)
The resistance on de N75 between the two pins is 37 ohm in my case, you shoud measure that too. It must be between 25 and 35 ohm.

Greetings from Bosnia!


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## softalino (Feb 16, 2009)

I also found a good article on some german website about the N75. It is a good way to test the N75. I will translate it and post it tommorow.


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## dogsoldier20 (Dec 3, 2006)

I had a dicky N75 valve on my old 225 coupe, I was out one night for a bit of spirited driving when I noticed the car pulling a lot harder than it normally would, thinking it must have been the cold air, I thaught nothing of it, after a mountain twisty section, came onto a roundabout, dropped it a few cogs then on exit planted it and there was nothing, there was a lot of wooshing noises and no go at all, backed off, floored it again and it went like a bullet again, untill the next roundabout, same again, and so forth, did some reading into it and found that it was signs of a N75 failure.
So one afternoon, got myself a bunch of new jubilee clips and decided to remove the N75 for a quick clean, I had nothing to loose, as it was knackered anyway, so I got a can of electronic PCB board cleaning fluid, Isopropryl I think, and gave the 3 ports a good squirt, the colour of the fluid when it came out was orange, so i kept on squirting untill it ran clear, left it to dry out for an hour or so, refitted it and went for a drive, all was fine, no spiking or flat spots, never gave me any more grief after that. It's worth a try £5 worth of cleaning fluid and clips or £40 for a new one.

You could always try an N75 race valve in it's place (The H or J variant I think), but they don't always work, they do on some 20V Turbo's but not all.

Rhys.


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## roddy (Dec 25, 2008)

dogsoldier20 said:


> I had a dicky N75 valve on my old 225 coupe, I was out one night for a bit of spirited driving when I noticed the car pulling a lot harder than it normally would, thinking it must have been the cold air, I thaught nothing of it, after a mountain twisty section, came onto a roundabout, dropped it a few cogs then on exit planted it and there was nothing, there was a lot of wooshing noises and no go at all, backed off, floored it again and it went like a bullet again, untill the next roundabout, same again, and so forth, did some reading into it and found that it was signs of a N75 failure.
> So one afternoon, got myself a bunch of new jubilee clips and decided to remove the N75 for a quick clean, I had nothing to loose, as it was knackered anyway, so I got a can of electronic PCB board cleaning fluid, Isopropryl I think, and gave the 3 ports a good squirt, the colour of the fluid when it came out was orange, so i kept on squirting untill it ran clear, left it to dry out for an hour or so, refitted it and went for a drive, all was fine, no spiking or flat spots, never gave me any more grief after that. It's worth a try £5 worth of cleaning fluid and clips or £40 for a new one.
> 
> You could always try an N75 race valve in it's place (The H or J variant I think), but they don't always work, they do on some 20V Turbo's but not all.
> ...


veree iteresting !! for a newbie can you please tell me where the N 75 is as i ( very seldom but somtimes ) have similar prob


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## rustyintegrale (Oct 1, 2006)

Hi Kev,

I have the S2 N75. 

What does it do? Apart from empty your wallet of about £35 which it definitely does it is also supposed to keep boost at peak for that little bit longer.

Let's call it Viagra for your right foot... 

Cheers

Rich


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## softalino (Feb 16, 2009)

This is a picture of an VW but it looks the same!!!


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## chrishTT (May 14, 2006)

my visit today to audi brough up the n75 as the n249 on etka
ordered both to see if these are my probs
but will be returning if they aint the prob
my n75 is on 94% on my liquid
whats others got?


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## dogsoldier20 (Dec 3, 2006)

It's on your Turbo Intake Pipe, the black pipe which goes from your Air Filter down to your Turbo, it has a few branches on it, your Diverter Valve is in one port, and behind that further up is the N75 valve, it is a solenoid valve with 3 ports and an electrical connector. If you remove your main engine cover, the one with 5V Turbo writen on it, the N75 is found under the back right hand corner of the cover.

Here's a pic for you to picture it better.









Hope that helps and I didn't over complicate it 

Rhys. 8)


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## dogsoldier20 (Dec 3, 2006)

Pipped to the post. :roll:

That's a better pic anyway, plus mine didn't work 

Rhys. 8)


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## roddy (Dec 25, 2008)

softalino said:


> This is a picture of an VW but it looks the same!!!


thanks stef i should be able to find it from there , give it a bit of a clean !!


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## softalino (Feb 16, 2009)

Here some more information:

The N75 has one connector with two pins.
Pin 1 goes from the N75 connector to the ECU pin 104
Pin 2 goes from the N75 connector to the battery supply via fuse 34.

*Testing the N75*
- take of the connector on the N75
- measure the ressistance between pin 1 and pin 2
- the N75 must have an ressistance between 25 and 35 ohm
- when the measured value is out of this range, the is N75 is not so good anymore









*When the engine is runneing*, take of the connector and measure the voltage on the two wires:
- on pin 1 you must have an voltage between 11 and 14 volt (that is the battery supply)
- on pin 2 you must have between 3 and 5 volt (that is the voltage from the ECU)
- if you mis one voltage than you have an broken wire (that was the case on my TT)


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## boosted (Jun 3, 2007)

rustyintegrale said:


> Hi Kev,
> 
> I have the S2 N75.
> 
> ...


Is that the N75'J'? I had one on my Ibiza Cupra and it made a fair difference down low, the boost came in much earlier and it peaked a wee bit higher too.

Found the C and F variants to hold the boost a bit higher top end though.


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## roddy (Dec 25, 2008)

dogsoldier20 said:


> Pipped to the post. :roll:
> 
> That's a better pic anyway, plus mine didn't work
> 
> Rhys. 8)


thanks anyway DS much apreciated


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## roddy (Dec 25, 2008)

softalino said:


> Here some more information:
> 
> The N75 has one connector with two pins.
> Pin 1 goes from the N75 connector to the ECU pin 104
> ...


good man you are 2 but sparks are not really my thing IYKWIM


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## zabzy-TT (Jul 9, 2008)

softalino said:


> quote]
> 
> Hi,
> 
> ...


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## softalino (Feb 16, 2009)

Your pressure at the intercooler is alot better than myn and the actual load is far more. What engine do you have (1.8T 180bhp or the 225??) Is it original (or chipped) and is the N75 original or race.


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## KentishTT (Jun 28, 2007)

Blimey, this post is a quarter of a year old :wink:

Thanks for the replies and info.


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## zabzy-TT (Jul 9, 2008)

softalino said:


> Your pressure at the intercooler is alot better than myn and the actual load is far more. What engine do you have (1.8T 180bhp or the 225??) Is it original (or chipped) and is the N75 original or race.


I have a standard 225 not mapped, no engine mods, i did the run in 4th gear if that makes any difference?


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## chrishTT (May 14, 2006)




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## softalino (Feb 16, 2009)

> I have a standard 225 not mapped, no engine mods, i did the run in 4th gear if that makes any difference?


The fact that you have an 225 can explain that your boost pressure and actual load is bigger than mine.
On saturday I will test another TT 1.8T 180bhp and I will compare this with mine to see what the differece is.


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