S3 Running fault

[IGI]

2002 S3 BAM

Hi car has been running poor past 2days read fault codes
17963 MAX BOOST PRESSURE EXCEEDED LIMITS - INTERMITTANT

Did actuator test of n75 valve - clicks away and had a look at hoses etc for leaks. Has anybody else had this fault ? any common faults? anything else i should be checking ?
Any info would be great thanks

 

[Ess_Three]

Is it re-mapped?
Std N75?

I used to get that - or a similar - error when I hit limp mode, because I was running silly boost/torque.

 

[IGI]

Is it re-mapped?
Std N75?

I used to get that - or a similar - error when I hit limp mode, because I was running silly boost/torque.

Hi nope car is totally stock and with std n75 think it may be leak, sounds like boost pressure is being lost somewhere and cuts the power under acceleration. This doesnt happen all the time other times pulls cleanly up the revs

 

[Ess_Three]

Does it feel especially torquey just before you notice it cutting the power?

Mine used to give that sort of code when it was cold weather (dense air) and high boost...then it would loose all boost, which is the limp mode that the ECU enters after seing a code like that.

If your car felt REALLY quick just before, it could be the wastegate sticking?
Giving maximum boost, maxxing out the MAP sensor, and hitting limp.

But on a standard car...I suppose unlikely, but possible.

Unless the MAP sensor is failing perhaps?
Giving strange readings, triggering limp mode.

 

[IGI]

Does it feel especially torquey just before you notice it cutting the power?

Mine used to give that sort of code when it was cold weather (dense air) and high boost...then it would loose all boost, which is the limp mode that the ECU enters after seing a code like that.

If your car felt REALLY quick just before, it could be the wastegate sticking?
Giving maximum boost, maxxing out the MAP sensor, and hitting limp.

But on a standard car...I suppose unlikely, but possible.

Unless the MAP sensor is failing perhaps?
Giving strange readings, triggering limp mode.

What youve described is basically what the car is doing when it does boost its more torquey than usual then cuts,sometimes along with a noise could be wastegate opening losing the boost pressure
Does the N75 valve control the diaphram at turbo that pulls the wastegate open?
Faulty N75 or wastegate diaphram

 

[Ess_Three]

I'd suggest the wastegate diaphram.

If the wastegate is sticking closed you'll get monster torque (more 315 lb-ft) as the boost builds - at about 2800 RPM I'd say - then you'll saturate the MAP sensor as it only reads to around 2750 mb absolute, and that will trip the ECU into limp mode...which basically removes the boost.

The N75 could be at fault...but I suspect it's more likely it would fail safe, and give less boost. Certainly if I were designing a boost circult I'd have it set 'fail safe'.

But if the wastegate is sticking, you'll get as much boost as the K04 will give, for a split second, before the MAP saturates and you hit limp.

 

[Dave B]

Is it re-mapped?
Std N75?

I used to get that - or a similar - error when I hit limp mode, because I was running silly boost/torque.

Should we upgrade our N75 valve if we have remap,
or is there an advantage to be had?

Sorry to hijack

Dave

 

[Ess_Three]

Should we upgrade our N75 valve if we have remap,
or is there an advantage to be had?

Sorry to hijack

Dave

Can you? Yes.
Should you? Not always...

The H or J N75s will give more boost, for sure...
5 BHP and 10-15 lb-ft in the case of my S3, running 1.89 bar of boost.

But, they can cause spiking and make things horrible to drive...or worse, cause the boost to go so high that you saturate the MAP and get the error that IGI is getting, and limp mode.

To run a different N75 on a re-mapped engine, in my view, you need to dyno it and log EGT, mixture, ignition timing and injector 'on' time as with a very aggressive re-map + N75 H or J, you could be running lean...injectors 'on' more than is considered safe, mixture goes lean, EGTs go up...timing tries to ****** to correct...or engine could go bang.

It works...the N75 swap.

Just be aware of what it can do...and make sure it doesn't/can't on your own car before you decide to run it!

 

[Dave B]

Cheers!

Any recomendations for a N75 valve my remap is not overly agressive and im willing to give it a try, if it goes bad I can always go back.
which one do you run?

I have the "225" variant engine if that helps

Thanks in advance

Dave

 

[Ess_Three]

I didn't run either...
My S3 was producing more power/torque than most and was very aggressive in it's delivery (average 270+ BHP and 320+ lb-ft)
The H valve gave 275 BHP & 332 lb-ft.
The J a little less torque IIRC.

Basically, either would max out the MAP sensor and hit limp mode.
I had an electronic MAP 'clamp' built which meant I could run either without hitting limp, but it wasn't nice to drive.
The H was espcecially aggressive...
A real hoot going sidewards off roundabouts with all 4 wheels spinning...but you had to really watch when driving it...dropping to the std N75 meant it was more usable, more of the time and hence actually faster point to point as you weren't fighting the car.

You will probably find you are OK to run a H or J, depending on who's re-map you have...and what peak boost you are making.

Any idea on peak boost?

EGTs/mixture/injector 'on' time etc are only truly a concern on the engines that are pushing the limits of the K04...so you need to be running 1.7 bar of boost or more to start worrying, I think.

Mine was OK at 1.89 bar peak, 1.3 bar sustained, but I was advised not to try a top speed run...6th gear and the turbo working that hard may have resulted in a melted engine....and I wasn't going to go there to find out.


Each car is different.
You really need to dyno to prove it's safe...and run it to see if you hit limp.
I did in winter when it was cold...but was fine in summer when it was warm.

 

[Ess_Three]

Oh, I'd try the H...purely because it's easier to fit.
It fits the same way as standard. The J doesn't.

 

[IGI]

I'd suggest the wastegate diaphram.

If the wastegate is sticking closed you'll get monster torque (more 315 lb-ft) as the boost builds - at about 2800 RPM I'd say - then you'll saturate the MAP sensor as it only reads to around 2750 mb absolute, and that will trip the ECU into limp mode...which basically removes the boost.

The N75 could be at fault...but I suspect it's more likely it would fail safe, and give less boost. Certainly if I were designing a boost circult I'd have it set 'fail safe'.

But if the wastegate is sticking, you'll get as much boost as the K04 will give, for a split second, before the MAP saturates and you hit limp.

Is there any values i should be checking for this i have access to a vag 1552 and snap-on solus, measuring blocks,values to compare against etc?

 

[Ess_Three]

Is there any values i should be checking for this i have access to a vag 1552 and snap-on solus, measuring blocks,values to compare against etc?

Yeah, you need to reset the faults...
Check there are no N75 related faults.

Then log requested boost vs actual boost. Or simply find the block for the MAP sensor and look at that as live data...if the value saturates at somwhere around 2750 (the MAP sensor reads absolute pressure, so will show 1000 ish off boost - basically atmospheric pressure on the day - and will saturate around 2750 mb absolute, or 1.75 bar boost.), then you are indeed getting all that boost...and it must be the wastegate stuck.

I can't remember the blocks though, sorry.

 

[IGI]

Yeah, you need to reset the faults...
Check there are no N75 related faults.

Then log requested boost vs actual boost. Or simply find the block for the MAP sensor and look at that as live data...if the value saturates at somwhere around 2750 (the MAP sensor reads absolute pressure, so will show 1000 ish off boost - basically atmospheric pressure on the day - and will saturate around 2750 mb absolute, or 1.75 bar boost.), then you are indeed getting all that boost...and it must be the wastegate stuck.

I can't remember the blocks though, sorry.

Cheers for the info i'l let you know when i get to the bottom of it, away to read up on some 1.8 t manuals