N75 VALVE - How do I change it? +Torque spike

[Jimmy D]

Hi guys,

I have been looking on the net for a while now but I have been unable to find a 'how to guide' for the removal and replacement of the N75 valve on a S3. I know its attached to the turbo but how are you supposed to get access to change the damn thing. I have been under the car and removed the under tray but the route to blocked by what looks like a heat shield along with other engine components.

I'm changing the valve as my car has developed a power spike around the 3300rpm mark. I cannot be sure if the valve is responsible but it cannot hurt to change it (I have also swapped the DV valve to a version 'D') My car runs fine and I have no error codes or warning lights displayed.

If anyone has any ideas what maybe causing the spike I'm all ears. Below is the dyno print out.



Note: I have had the car remapped recently in an attempt to iron out the spike but it has made the spike worse. Anyway my car is stock expect the stage 1 map.- 2007 plate with 40 odd thousand on it. The cam belt has also been changed within the last 6 months.

Cheers

Jimmy

 

[Craig Cull]

Hi guys,

I have been looking on the net for a while now but I have been unable to find a 'how to guide' for the removal and replacement of the N75 valve on a S3. I know its attached to the turbo but how are you supposed to get access to change the damn thing. I have been under the car and removed the under tray but the route to blocked by what looks like a heat shield along with other engine components.

I'm changing the valve as my car has developed a power spike around the 3300rpm mark. I cannot be sure if the valve is responsible but it cannot hurt to change it (I have also swapped the DV valve to a version 'D') My car runs fine and I have no error codes or warning lights displayed.

If anyone has any ideas what maybe causing the spike I'm all ears. Below is the dyno print out.

View attachment 28044

Note: I have had the car remapped recently in an attempt to iron out the spike but it has made the spike worse. Anyway my car is stock expect the stage 1 map.- 2007 plate with 40 odd thousand on it. The cam belt has also been changed within the last 6 months.

Cheers

Jimmy

It's definitely worth changing mate, for the amount it costs.
On the golf gti's you can remove the off side front wheel arch liner, this gives access to the diverter valve. I realise yours is different, but It may give you a chance of getting to the N75 as it's on the same side but slightly to the right. I think you will have more chance of getting it from the wheel arch as apose to underneath. Got to be worth a shot

 

[Rick @ Unicorn Motor Dev.]

The S3 does have a spike as std, but that looks excessive. Before you start changing things, it's best to see what the ECU is actually asking for. Does it register a boost spike? Is it holding the N75 open for too long? From there you can home in on the issue.

Rick

 

[Craig Cull]

Rick knows his sh*t lol! Mines a weapon thanks to him lol!

 

[Jimmy D]

Right , ill get it logged and see what's happening before I attempt to swap the valve. To be fair the car seems to run fine when driving it. I'm getting the impression its not a 15minute job. Thanks all

 

[Rick @ Unicorn Motor Dev.]

Is it just on the dyno you have seen the spike? Or was there a problem on the road? It could just be the dyno ramp rate is exaggerating the spike.

Rick

 

[Jimmy D]

That's just on the dyno, my mate who has the same car run his straight after mine and his was pretty flat. Yyou can feel the power surge under acceleration but its not causing me any problem, its just a shame it doesn't hold all that torque.

 

[Craig Cull]

That's just on the dyno, my mate who has the same car run his straight after mine and his was pretty flat. Yyou can feel the power surge under acceleration but its not causing me any problem, its just a shame it doesn't hold all that torque.

Might be a long shot, but have you gone for the RS4 fuel pressure return valve?