Overboost and the N75 output test - N75 not fully sealing?

[TheNumber13]

Hi,

2003 Audi S3 BAM, stock parts, probably mapped.

My main question is do I have a faulty N75; the actuator outlet does not completely seal:
I performed the N75 output test with VCDS and blew in the bottom/input. It cycled between diverting the air out the TIP outlet and the actuator outlet as it should. However when it was sending it out the TIP, there was still a bit of air coming out the actuator outlet. Is this a faulty N75?

Should it completely seal the actuator outlet?

If I'm correct in thinking it should seal completely, I assume this could this be leading to an overboosting issue?

And a bit more info specific to my situation:
-I have been having a boost spike of between 17-20psi at around 3,500-4000rpm, after which it drops down to 13-14psi. Requested is around 15psi the whole time.
-No N75 fault codes. Very occasionally '17963/P1555 - Boost Pressure Control: Upper Limit Exceeded'. Also two pre-cat lambda codes, new lambda is on its way to fix fuelling issues.
-Car is 100% stock parts from what I can see. I believe it must have had a map/tune before I bought it. Looking into quality of this map is next on my list, after fixing overboost and getting a smoke test

I've included a couple of 115 and 118 logs (2nd gear only, its wet and dont want to get too illegal on my slow local roads).

Thanks for looking, I normally try and sort everything out from the heaps of info already on here, but just want confirmation of dead N75 before buying a new one.



Cheers

 

[badger5]

if its still passing air to the actuator its not going to be an overboost is it.. think about it

go log n75 duty cycle on 118 as well as 115 to see what its being told to do

the request being early does'nt mean its actually possible to achieve that....

 

[TheNumber13]

Argh, thanks Badger. Had my understanding the wrong way round, think I got it now with further reading.
I never expected to get the boost as early as it's being requested, was actually suprised to see how much it was asking for so early (starting to think may be dodgy map on the car before I got it).
My main concern was the spike way above requested, but since the N75 duty cycle (118 + 115 in first post) backs off beforehand, and the boost continues up to spike, I guess it's not the problem I thought.

So much for that solution, back to plan A; -Replace pre-cat lambda when it arrives, more research in the meantime. Get more detailed logs and a smoke test once it's in, try and see whats going on with my map/tune.

Cheers for your input, much appreciated

 

[badger5]

not unusual for an overshoot if the map has'nt been dialed into the car and runs std boost control PID etc....
It does'nt have to be this way however when tuned accordingly

 

[TheNumber13]

Legend.
Thats what I was worried about. I'll get a better idea once I know the cars physically in order.
Thanks mate.

 

[badger5]

remember your logging is limited to seeing max boost of the map sensors range.. 2550mb.. (1.5bar boost)
the spike may exceed this so other "gauging" should be used to verify how far it overshoots..