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prj
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« on: May 27, 2012, 03:26:47 AM »
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In the tune I got with my RS4, SDLDSUA is FF'd.
Which as I understand means that the N249 is not pulsed.
Has anyone found that the N249 gives actual benefits to fuel economy? Or is it there mostly as a safety device?
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prj
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« Reply #1 on: May 27, 2012, 01:18:30 PM »
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Alright, I noticed that only the end of SDLDSUA was FF'd, so at pressure levels above 1920mbar.
Basically it predicts the boost change within the next PIDLDSUA*10msec, and if the predicted boost drop is bigger than the current value in the SDLDSUA table, as well as the the throttle pedal is lifted more than GWPLDU, it engages N249 and opens the dump valves.
This is to facilitate faster opening of the valves, than a direct vacuum source could do alone. This is especially important at lower RPM's, as at higher RPM's there is plenty of vacuum to overcome the spring pressure of the diverter valves.
The 1.8T FR talks about KFSDLDSUA, which is RPM by plsol, but in the 2.7 ECU's it seems to be just plsol.
This stuff can't engage unless the throttle is lifted slightly, so I don't see the reason it was FF'd in the first place. On a WOT run it will never engage.
However, it /was/ changed to RPM by plsol in later Motronic revisions, which hints at the fact that using just plsol was inadequate, and caused some sort of issues? The application hints also show a FF'd KFSDLDSUA table at anything above 4400 rpm.
Comments?
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« Last Edit: May 27, 2012, 01:20:02 PM by prj »
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RS4boost
Full Member
Karma: +46/-0
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Posts: 125
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« Reply #2 on: May 28, 2012, 06:16:33 AM »
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Hi,
it makes no sense to set SDLDSUA to FF at hight pressure.
I know non reputable tuner who do this for this ECU.
If you do this, the boost can not escape by a closeing throttle and both turbos runs out of the surge line of the compressor map, because in this moment there is no air flow to the engine.
This will generate hard shock waves inside, which damages your turbos sooner or later.
If you increase the values only a little bit, you will have a better response from the engine at shifting in the next gear, because the boost pressure will reduced a little bit slower.
Tom
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« Last Edit: May 28, 2012, 06:18:15 AM by RS4boost »
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prj
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« Reply #3 on: May 28, 2012, 07:50:50 AM »
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Hi,
it makes no sense to set SDLDSUA to FF at hight pressure.
I know non reputable tuner who do this for this ECU.
If you do this, the boost can not escape by a closeing throttle and both turbos runs out of the surge line of the compressor map, because in this moment there is no air flow to the engine.
This will generate hard shock waves inside, which damages your turbos sooner or later.
If you increase the values only a little bit, you will have a better response from the engine at shifting in the next gear, because the boost pressure will reduced a little bit slower.
Tom
Well, the dump valves can still be opened mechanically. Whether there is N249 signal or not. The N249 signal is needed only at low rpm's and high boost, where there is not enough vacuum fast enough to open the valves. So I don't think there will be a problem on higher RPM at all, but on lower RPM... yes... |
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professor
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« Reply #5 on: July 19, 2012, 12:18:13 PM »
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Welcome back Tony  |
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Seat Ibiza MK4 Cupra 1.8t 20V, stg3.
"Those 1.8T 20V machines are really tough" ©
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TTQS
Guest
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« Reply #6 on: July 21, 2012, 11:19:16 AM »
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Great discussion and thanks for unearthing that patent. I recall discussion on deleting N249 between 1.8T owners on other forums but the real reasons for the valve never got explored other than it was a "safety feature". I paraphrase the key points of the invention summary so we've got the text handy within this thread: ... [the N249 valve] prevents the recirculation/dump valve from being prematurely closed by the negative intake duct pressure on the downstream side of the throttle valve in the event of rapid closure of the throttle valve due to pumping of the boost air column. The boost pressure is uniformly and continuously decreased. Boost pressure fluctuations, and jerking of the vehicle caused thereby, are prevented.
It is advantageous for [ECU intervention via the N249 solenoid valve to occur] if:
1. the load gradient of the engine exceeds a threshold that depends on reference boost pressure. (The load gradient can have a predictive value superimposed on it if the current load gradient has risen as compared with the load gradient existing one timing cycle earlier.)
2. the absolute intake duct pressure lies below a pressure threshold at which the air recirculation/dump valve would open. (A control signal to activate the solenoid valve should then be made available if the absolute intake duct pressure exceeds the pressure threshold.)TTQS |
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prj
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« Reply #7 on: July 21, 2012, 11:24:10 AM »
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Basically, imagine that every time you close the throttle, you are rapidly approaching the surge line on the compressor map.
With just vacuum operated dump valves alone the vacuum is not enough on low loads to overcome the spring pressure.
However, if the ECU can preemptively open the valves, then you will not hit the surge line...
I think this is the main reason to leave this enabled.
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BlackT
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« Reply #8 on: April 08, 2022, 12:58:27 PM »
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Is it possible to set that ECU open DV when: Pedal is more than 80% and boost pressure actual is 200 mbar above boost pressure desired?
I am looking at FR but can't get it
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BlackT
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« Reply #9 on: April 09, 2022, 11:36:33 AM »
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Ok I think I get it
I set GWPLDU to something over 0, I put it 2% (original is -3.xx)
Now every time my boost + SDLDSUA is above plsol, DV open
It is not related to pedal position because SDKSUA can only work opposite way, but I am fine with that,
Will test and report does it infer with anything else
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