Can an increase in WG spring induce surging?

[A80Avant]

My wastegate spring is being wound down(not all the way) but enough to make the boost climb to 1.5bar towards the end of the rev range with the WGFV unhooked.

I was wondering... can that fact induce more surging when going WOT or is that irrelevant?

My map was done with the spring on the original position,however it always seemed to me that boost pressures were never met,so that is how i started tampering with it.Now EGTs and boost pressures are met,but on 5th and 6th gear WOT from 3000rpm,it tends to show some surging here and there,before the boost settles at 1.9bar.

i was wondering if the wastegate spring has anything to do with it.

cheers
vasilis

[Rusty]

Yes, the WG spring can induce surge if it's too tight for the turbo, it means that the boost increases much more sharply. Put it back to near standard, it might take a bit more pre-load but you only need that if the WG is creeping really. Better to wind the spring out and prevent surge.

[A80Avant]

i see!
thanks
im going out for testing...!

[Rusty]

Disconnect N75, set WG sping to 0.4 bar (stock setting) on your boost gauge. Test it at this setting. If you get boost creep then tighten the WG spring and then test for base boost with the N75 unplugged. Repeat. Note WOT pressure at each point both with & without N75, this will give you a reference value for when you are happy with it. I set mine to 0.6 bar with no difference really so I put it back to 0.4 bar as that's what my map is set for. Possibly getting a map for stiffer WG spring...

[A80Avant]

right,
just got back.
I may have some kind of issue,but i cannot pinpoint it.

When the car was mapped + all the updates of the map,were done on basic OEM spring,without any tampering of the screw(as i didnt have it removed back then).SO the map that im supposed to have should give me 1.9bar overboost,hold that up until 6000rpm,then drop to 1.7bar to 7000rpm then to possibly 1.6bar to the redline(7300 or so.)

Went out,unwound the WG spring,got in, N75 unplugged, got me the 0.4bar all the way! SO nice OEM setup.

I then connected the N75,and here are the boost levels i got:

3d gear: 1.5bar initially,climbed to 1.7bar for a few rpms,then dropped to 1.4-1.3bar!!!
4th gear: 1.7bar and kept 1.5bar to the red line!!!

I dont have any leaks on the boost,it goes nicely,no error codes,everything checked and accounted for!

Am i right to assume that there is something wrong with my wastegate?
How can the map ask for so big boost numbers and im getting so less in real time??,AND it is covered by fueling as well(when i was boosting 1.5bar to the red line i had like 820C only!)

I dont understand!

[A80Avant]

could this be a faulty map sensor in the ECU?

[Rusty]

Your boost gauge might not be that accurate, my boost gauge didn't always correlate with that on a rolling road. Fuelling suggests that's not the case tho.

If your wastegate diaphragm is tired then it might leak a little?

Did you try winding the WG spring in a little to cure the problem? Not as much as before tho. What was it set at originally to cause the problems?

[A80Avant]

i did try to wind up the spring.
did it in steps and the boost was gradually coming up to the specified levels.I stopped winding it just a tad of what i had it before.

If the diafragm was torn,wouldnt i be getting weird acceleration? the car goes nicely in any occasion,in any boost level.

Just to make things more complicated...
When i was in greece a friend of mine had recently finished his rs2 same spec as mine,only with the OEM interooler in place.
He had just finished his remap,but we had a chance to try my map as well.
On his car the car was reaching 1.9 to 2.1bar easily with wastegate spring at 0.3bar!!!

how can we explain that?
could i have a faulty map sensor?

[Rusty]

Could be that the temperature compensation map as per ABY is coming into play? I didn't think this existed on ADU? If you're running in the 0degC temps in the UK and comparing to 30degC in Greece then this would cause the same issue on an ABY chipset. Paul is the man to ask about this...

[A80Avant]

but sobig difference??

[A80Avant]

i know about this and i think Erdal has indeed incorporated something like this in the chipset,however if i remember correctly should have made it the other way around,meaning more aggressive in the cold weather,less aggressive in hot weather,since when it gets hot in greece,it does indeed burn! So having the car going fast then would eventually give knock or retard ignition timing.

[Rusty]

My S2 should see 21PSI but with RS2 IC and cold weather it sees 18PSI so yes, it can leade to a big difference.

[A80Avant]

i need to investigate this further
next week i will be in Greece for a week and i will have the motronic with me.I will test my motronic against my friends motronic (with the N75 connected of course) to actually see if this is an ECU problem or a wastegate problem.

I still wonder,if this is a map compensation issue,then why is it when i was in Greece i still had to do the same thing with stiffening the spring?If i remember correctly,i had to stiffen the spring in all maps i had as updates.
However my friend's motronic is able to reach the boost levels easily.(last time i was there when we tried it,it was also quite cold, about 8C so that should be corrected as well.

[A80Avant]

Also i need to mention,if that makes any sense,that when the spring is set to 0.4bar the boost is reaching the lower levels mentioned abruptly and steadily,there is no sign of any creep or struggle.It is as though the map was made to reach those excact levels of boost.

[JP]

Two things to look at that I have come across in testing in my motor which is sensored up to the hilt with different chipsets. 1 - colder the weather the more susceptible the MAF is to topping out at 5v and giving symptoms of surge, a good map can get around that issue by filling in the black spots. 2 - the N75 valve has only got tiny holes in it to sense boost changes over time these get clogged up and give erratic boost control. Be worth replacing this. Very much doub from what I have learned from experimentation that you have a wastegate issue.