Stock RS2 boost pressure too high

[Berjamin]

Hello team,
I have been member for long time but due to different circumstances i was not active for while. I am glad to be back and I need your help

I am having an issue with boost pressure with my RS2 and I am running out of ideas, so I will appreciate if anybody can give me any input that might halp point me in right direction.
To the problem, car ist completely stock and it started having issues with boost levels going too high, basicly if I make pull in 3rd, 4th or 5th gear for example boost will goes to 1,6-1.8 bar and I notice that is not pulling right once it goes past 1.4 bar (which sould be max pressure as far as I know). Boost does fall back but it never reaches 0.9 bar level , here too it stays higher aroung 1.1-1.2 bar. It runs great on idle and pulls very strong until it goes past 1.4 bar and currently will not drive past 220- 230 km/h.

What I have done so far:
- Checked for fault codes with VCDS - no codes what so ever except one for crank sensor but I know that is ok when engine is not running
- Checked my boost gauge by adding another one and connecting near ECU - boost level same as my gauge installed in car permanently
- Checked for boost leaks using 1.4 bar pressure - one very small leak at IAC valve on conector side. I replaced this valve with new one coule years ago but it was barely driven since then
- Wastegate hast been rebuilt few years ago by very reputable person here in Germany, so I assume that is fine
- Checked membrane using vacuum pump on top port - hoding vacuum 100%
- Checked hoses from turbo to N75 and from N75 to wastegate , no issues
- Replaced N75 with brand new one from Audi, with same Part number and index - no change
- Checked - hoses from Intake manifolt to ECU including moisture trap using smoke maschine . no leaks found
- Connected another line temporarily from Intake manifold to ECU - no change, boost still too high

I at the point where I assume that MAP sensor inside ECU is probably defective becase it probably interprets actual boost level lower that it is. I dont know how to check this and I dont think I ever heard people having issue with factory MAP other that replacing it if they are runnung higher boost levels than sensor can handle. Also what is interested is that ECU does not set fault even boost reaches level way higher that it should, so to me that is another indication that MAP sensor is not doing its job, but since I am not sure I hope someone here can help

As I said I am running out if ideas, so any suggestions are more than welcome.

Thanks in advance
Berjamin

[le mans]

I believe the stock hard cut boost limit on RS2 is 2.09 bar (309kpa absolute) so 1.8 bar may not register an error code.

The only personal experience I have with over boosting on this platform involved an incorrectly plumbed N75 (aftermarket ECU). If your N75 plumbing hasn’t been changed then you can rule that out. That then leads me to think perhaps the wastegate is stuck and needs a refurb?

Regarding your theory about defective internal map sensor, I suspect that would trigger an error code, but cannon be sure.

[Berjamin]

I did check the plumbing for N75 as I was installing a new one. I found plenty of info here on forum what ist correct orientation and I also checked hoses going from turbo to N75 and from N75 to wastegate.
Wastegate was rebult in 2019 by guy that is known here in Germany for doing it right. It has been while since rebuild but I have not driven car much since then due to whole situation with corona and so on.

I should probably mention that here in last few week was very hot, like around 40 °C, so would that cause the boost to be higher than normal? Even if it does, I suspect car should run right and have normal power, right?

[Berjamin]

I was checking measuring blocks values yesterday and it seems that there is no measuring block for MAP sensor. Is that true? There is value of altitude sensor but not for MAP as far as I can see

[LHD_Kid]

Have you tried running with the N75 unplugged, see what pressure you get?

[Berjamin]

Have you tried running with the N75 unplugged, see what pressure you get?

Yes i did, I get 0.6 bar exactly

[K Simmonds]

Baseline boost with the N75 unplugged should be 0.4 bar, peak boost with it plugged in should be 1.6K.

Could you try an ECU from another car? If the problem goes away then you know it's probably the MAP sensor. Though it's more likely to be be something mechanical, the wastegate is the most likely part to be at fault if you've tried two different N75's, even if it was rebuilt a few years ago it could be sticking.

[Berjamin]

Baseline boost with the N75 unplugged should be 0.4 bar, peak boost with it plugged in should be 1.6K.

Could you try an ECU from another car? If the problem goes away then you know it's probably the MAP sensor. Though it's more likely to be be something mechanical, the wastegate is the most likely part to be at fault if you've tried two different N75's, even if it was rebuilt a few years ago it could be sticking.

I apologize, it was 0.4 bar, it was typo from my side.
I went to talk to guy that owns PK Motorsport here in Germany, I dont know if his work is know here in forum but he did not think that boost that I am seeing is that problematic. He thinks that car is running rich and that is why it dont pull all that great in higher loads (suspect is mass airflow sensor, which as we all know is not available any more). I did borow air/fuel measuring device and i will measure next chance I got to see if that holds true or not.
Also he took car for test drive and told me that usually RS2 should at 2900 Rpm reach full boost and my car reaches it at 3200. I dont know if that is sign of maybe trubo being still original and somewhat "tired" or its related to boost issue I am chasing.

Unfortunately he did not have MAF or ECU that I could try, so I have to try to solve this any other way I can think of

[hashluck]

Have you checked your Diverter Valve (lives under the N75 Valve)?

[le mans]

From what you've said the wastegate is likely mechanically ok.

Factory boost pressure is 1.3-1.4 bar at 3000rpm (2300-2400 mbar absolute). This applies even in hot conditions.

[Berjamin]

Have you checked your Diverter Valve (lives under the N75 Valve)?

Diverter valve is new, but i did take it out and did visual inspecion anyways. Also I checked membrane using vacuum and since i checked for boost leaks using 1.4 bar pressure and found no leaks that would mean that divertar valve is not leaking.

[Berjamin]

So here is update on my situation. Since I was runing out of ideas I went back to basics. I do run adjustable cam gear because last time i did timing belt, i replaced cam seal and had to remove cam pulley. At that time i noticed that key on pulley had broken off and since original pulley is NLA I had no choice but to install adjustable one.
So went ahead and took timing belt cover off and valve cover to check if everything is where it should be. What I found is that cam pulley was adjusted half tooth off in retarded direction. I used S2 pulley (unfortunately i dont have my original cam wheel anymore) installed it on cam and lined it up with groove on valve cover, then took it off and installed adjustable pulley and line was half toot off to the right ( retardet direction)- Now dont scream at me, I know that once everything is timed right mark on pulley is about half tooth off to the left on RS2. This was just my way to check if pulley is adjusted correctly since there is no difference where timing mark on pulley sits between S2 und RS2, difference is in trigger wheel position.
I readjusted the pulley , installed it back on, threw timing belt back on, checked timing , crank was TDC on flywheel side, and cam was half tooth off to the left (advanced)
Took car last night on Autobahn and now it reaches 262 km/h top speed. Overboost problem seem to be better, i stll see boost goes to 1.6 bar and drops down to 1.0 bar but maybe that can be also tolerance of boost gauge.

I now know that pulley is now properly adjusted to be same as original as far as the part where belt rides on, but trigger wheel is adjustable also so I used some pictures here from forum where the difference in position between S2 und RS2 wheel is to be seen. Based on this I think trigger wheel ist good.

Does anybody have by chance original RS2 Cam wheel that is willing to sell it? I think this would be best solution for me, since I dont plan on tuning this car other then just good chip set.