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Author Topic: Controlling boost pressure with throttle plate under spring cracking pressure  (Read 1472 times)
olobolo1996
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Hi there,
 I am trying to understand how to control my boost with throttle when WGDC is 0%. I have read S4Wiki and probably every post on Nefmoto covering this, but still can't get my car to run as it should.
First of all the car:
Audi TT mk2 2.0 BWA MED9.1 with K03 hybrid turbo, custom intake (MAF housing same dimensions as stock) and 3 inch custom exhaust de-cated.
My current mods:
Audi S3 BHZ KFMIRL and KFMIOP



Tweaked KFLDRL and KFLDIMX, so I just need to adjust IMX (no seperate linearisation map)- take note it is a very basic map now, it is still under my development.



And now to my problem/problems:
I found on S4Wiki section about Base boost and wastegate spring pressure.
Quote
With aftermarket and/or tighter wastegates, you may experience bucking and choppy throttle response in part throttle near waste gate cracking pressure[29]. The throttle angle desired is dependent on the boost pressure in a turbo car since after a certain angle, throttling losses are negligible and it is better to hold the throttle wide open. But if the turbo cannot be controlled at that boost pressure via waste gate control any longer (because the wastegate no longer can open at that pressure), the ECU needs to be told to continue to use the throttle (and not got WOT) up to the new, higher boost pressure to regulate torque instead
I think this is what I am looking for. What I want to do is to use my throttle to lower pressure in the intake manifold when wastegate is 0% and car is still overboosting. In my case this situation happend when cruising around 120kph (2500+ RPM, accelerator pedal 25-30%)
S4Wiki says:
Quote
To correctly determine how much throttle opening is required to produce the amount of torque requested and prevent the ECU from going WOT prematurely, a few maps have to be tweaked in the module LDRPLS to set the base boost pressure in the ECU. The maps that set base boost are:

KFVPDKSD - Target pressure ratio in dynamic operation
KFVPDKSE - Target pressure ratio in steady state operation

Here comes first problem: In all damoses for MED9.1 there is only KFVPDKSE, no KFVPDKSD. Is it true? There is only this one?
Second problem: KFVPDKSE has different vpssplg_w axis to what I've seen in ME7. Now I should add that in CWPLGU I have "1" value, which means that in my ECU vpssplg_w should be equal to requested boost (absolute pressure)/atmospheric presure.
As you see below values of my KFVPDKSE are <1, which would mean that values of vpssplg_w axis are negative boost Roll Eyes
I suspect that in MED9 wpssplg_w axis represent something like (requested boost-atmosperic pressure)/atmospheric pressure


Assuming I am right let's move on.
On S4Wiki I've read that KFVPDKSE values below PSPVDKUG (0,95 in my case) represent areas where requested boost is below spring/cracking pressure which means that even if WGDC=0%, the wastegate reamins closed. So the row in which value exceeds 0,95 should indicate my stock spring/cracking pressure which in my case should be 0,420Bar.
Since I wanted to check if I am right, I've changed all values over 2500RPM of KFVPDKSE to 0,94. This should prevent ECU from going WOT. After that I've changed values over 2500RPM of WDKUGDN to 10%, cause I wanted to see if it will limit throttle angle to 10%. It didn't  Cry What am I doing wrong?Huh Please help.
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nyet
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WWW

You may need to do dissassembly and/or log more of the FEUDK path. In particular, log vpsspls_w to make sure it is doing what you think it is doing.

I'm unfortunately not familiar with MED9 so I'm afraid I can't give you more useful or detailed information. Please keep us updated on your progress.
« Last Edit: December 08, 2019, 01:41:39 PM by nyet » Logged

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olobolo1996
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Hello Nyet. Thank you for your reply. At least you ensured me that, to some degree, my thinking is correct. Also thank you for your translations of FR chapter. I found them really helpful to understand structure of ME7 system! Cheesy
I've found complete translation/english version of ME7.3 FR which can also be helpful. Link below: https://vdocuments.site/fre07e0-rtp.html
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vwaudiguy
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Looked through a small handful of MED9 complete a2l's and did not see KFVPDKSD in any.
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olobolo1996
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Thanks a lot vwaudiguy. Smiley
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olobolo1996
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It’s been I while. I’ve investigated Bosch documentation many many many times and turns out nothing is as simple as I thought. In the and it all comes to basic boost pressure. Properly adjusted basic boost pressure map helps a lot with proper PID boost control and throttle control.
Generally in my case of MED9.1 throttle plate is controlled like this:
Map KFWDKMSNVP gives two variables:
One called wdkobugs which is determined from mnsdkoos and pspvdb_kge. This angle goes through some filters, diagnosis etc to the throttle body. You should not touch this because it is perfectly calculated to the stock throttle body.
Other wdkugd is determined also from KFWDKMSNVP but from different data: msndkoug and PSPVDKUG whis is always 0,95
These two base throttle angles are compered and the lower value is selected. If the wdkobugs is lower, it goes through some filters etc do the throttle body.
If wdkugd is lower then some value is added to it and then it goes through the filters, blah blah and finally to the throttle body.
The mentioned value is calculated like as follows
1-wdkugdn*(vpsspls-0,95)/1-0,95
vpsspls value comes from KFVPDKSE
BUT
If pssol/plgru is lower than VPSPLGUG=0,95, then vpsspls=VPSPLGUG=0,95
When we put it into the equation, it gives us 0.
This is how the MED9.1 controls boost pressure under spring cracking pressure.

It all looks and works beautiful... BUT I STILL HAVE A PROBLEM
When cruising at around 3000RPM at 6th gear with just a little throttle, my actual pressure is around 1400-1500mbar absolute, while requested is around 900mbar.
How do you fix this? I dont want to raise KFMIRL in this area, because it will cause the throttle to open further and thus to accelerate.
Rising base boost here doesnt help.
Should I mess around with KFWDKMSNVP?
As always: please help!


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olobolo1996
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Below you can find logs and link to them


Link (click on the second tab):
https://log.tunezilla.com/s/nmQKllaQ
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