New S2 Avant Nothelle N300 owner

[Tractor Dave]

I did some maf testing today following UrS4boy’s helpful guide. All the numbers are good and everything seems ok. I cleaned the connectors again for good measure.
I also replaced the last bits of old vac pipe left. These were the short lengths next to the ecu.
I will do another boost leak test again tomorrow.



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[Ian Simmonds]

Well done fixing yours. All my vac pipes are new. I'm still looking for my bug

I followed this -

https://forums.quattroworld.com/s4s6/msgs/20987.phtml

and in particular the vacuum schematics on page 6

[Tractor Dave]

Well done fixing yours. All my vac pipes are new. I'm still looking for my bug

[Ian Simmonds]

Only through N75.
ECU modulates N75, reducing pressure applied to the bottom chamber of the wastegate.
In limp mode the N75 is left open to the wastegate which will open at spring pressure.
If you were to disconnect the hose from the WG (and plug it). The WG would stay closed and the car would overboost till the fuel is cut.

Have you checked that your ECU is seeing boost pressure? It’s been known for the boost/vac line from the inlet manifold to leak or be disconnected at the moisture trap under the carpet on the uk passenger side.
The small cotton covered vac lines at the back of the inlet manifold are usually leaky if still original.

John, see this thread..
https://www.s2forum.com/forum/member...me-love/page13
You utter star!

[newsh]

Interesting point John and something for me to investigate further. Genuine question, (because I really don’t know) is N75 the only way the ECU controls/reduces boost or can it control load through ignition timing and fuel?

Only through N75.
ECU modulates N75, reducing pressure applied to the bottom chamber of the wastegate.
In limp mode the N75 is left open to the wastegate which will open at spring pressure.
If you were to disconnect the hose from the WG (and plug it). The WG would stay closed and the car would overboost till the fuel is cut.

Have you checked that your ECU is seeing boost pressure? It’s been known for the boost/vac line from the inlet manifold to leak or be disconnected at the moisture trap under the carpet on the uk passenger side.
The small cotton covered vac lines at the back of the inlet manifold are usually leaky if still original.

[Ian Simmonds]

This is weird.
If you remove the N75 and fit a manual boost controller you should be able to turn the boost up. So there must be something physically wrong.
WG is very worn and opening itself by leaking through the valve guide.
You have a leak which blows above 0.7bar (but I’m sure you would hear that whooshing)
DV is broken or plumbed wrong.

Interesting point John and something for me to investigate further. Genuine question, (because I really don’t know) is N75 the only way the ECU controls/reduces boost or can it control load through ignition timing and fuel?

[Tractor Dave]

These cars certainly keep us busy

[newsh]

My (long!) process of elimination included power and continuity checks to N75 and MFTS (connected or disconnected), Swapped N75 and ECU (to an N300 vice MTM) put standard spring back in wastegate and vacuum checked for leaks, temporary replaced N75 with a turbosmart boost control (eventually ending up with it wound all the way out), removed air con belt. Car has full set of Roose boost hoses and a rebuilt turbo (last year). Throughout all of this it resolutely won’t go above 0.7 bar of boost in any combination.

This is weird.
If you remove the N75 and fit a manual boost controller you should be able to turn the boost up. So there must be something physically wrong.
WG is very worn and opening itself by leaking through the valve guide.
You have a leak which blows above 0.7bar (but I’m sure you would hear that whooshing)
DV is broken or plumbed wrong.

[Ian Simmonds]

I was thinking the same thing yesterday and looking them up online. I'm just wondering if VCDS can be run whilst driving and can you view any real time values to see what's happening?

My (long!) process of elimination included power and continuity checks to N75 and MFTS (connected or disconnected), Swapped N75 and ECU (to an N300 vice MTM) put standard spring back in wastegate and vacuum checked for leaks, temporary replaced N75 with a turbosmart boost control (eventually ending up with it wound all the way out), removed air con belt. Car has full set of Roose boost hoses and a rebuilt turbo (last year). Throughout all of this it resolutely won’t go above 0.7 bar of boost in any combination.

[Tractor Dave]

Yeah, I’ve chased my tail all day long with all manner of options. I’m thinking knock sensor now.

I was thinking the same thing yesterday and looking them up online. I'm just wondering if VCDS can be run whilst driving and can you view any real time values to see what's happening?

[Ian Simmonds]

Yeah, I’ve chased my tail all day long with all manner of options. I’m thinking knock sensor now.

[Tractor Dave]

Took her out for a long drive. Still cutting boost after doing the fuel pump relay so stopped and pulled the MFTS. Made no difference. I have boost to about 1 bar, then cuts. Perhaps I need to do another boost leak test

[Tractor Dave]

It's been so wet here I haven't taken her out. Hopefully, this weekend I can do some test runs. I suspect a poor earth on the fuel pump plug may have been a contributor. If the pump wasn't able to keep up on boost, it would cause weak mixture and cut boost. The earth wire was damaged where it enters the plug. I will report back after some tests

[Ian Simmonds]

Hi Dave, any more luck on the N75/MFTS/Boost issue?

[Tractor Dave]

I did the fuel pump relay mod today.
The only difference from the very helpful guide on the forum is that I ran new cables all the way to the pump connector. I didn’t like the look of the plug and wanted new wire all the way.
The plug


New connectors. I’ve use insulated female spades here with adhesive backed heat shrink.

The relay slots into one of the spare holes under the seat.

All wrapped up in new tessa and after double checking all my connections, car started to test.


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