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Author Topic: ME7.9.10 - Understanding the torque model  (Read 17012 times)
IamwhoIam
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« Reply #210 on: May 16, 2018, 10:22:39 AM »

long term trims on VAG are rkat_w and fra_w as far as I can remember
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I have no logs because I have a boost gauge (makes things easier)
woj
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« Reply #211 on: May 16, 2018, 11:47:02 AM »

There is no doubt about fra_w.

I looked at both rka_w and rkat_w, and actually, rka_w is the one that is applied at the end of the day. rka_w is either directly rkat_w (if a bit on one of the codewords is set, can't be bothered to check what codeword that actually is, but it is not on in my bin anyhow), or rka_w is derived directly from rkat_w with the help of the current nmot (some sort of rpm dependant scaling, again, can't be bothered to dive into this). So it probably does not really matter, provided one of them is logged.
« Last Edit: May 16, 2018, 11:49:47 AM by woj » Logged
woj
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« Reply #212 on: May 17, 2018, 12:42:53 PM »

I wonder if anybody has enough experience with E85 to help me ball park my cranking tables (FKSTT). On the first attempt (the _old file in the attachment) I looked up factory tables in the Saab files I was pointed to elsewhere here. I figured out their meaning / unit (or so I think) and converted them to my FKSTT E85 table that blends with the factory one (top of shots). The values seemed excessive to me, "but then, what do I know about diamonds", I just decided it's the best guess I can do.

Well, it isn't. Warm starts are OK, but "cold" (~20-25*C after long stay, that's the weather we have now) are not. The car starts on the first attempt, but rpms choke down to ~500 for a while and then it comes to life (the symptom happened twice, consistently the same at similar temperatures). Clearly overfueled, not to mention the fuel smell. And that is on 22% content, so the effective factor for these temperatures was ~7-8, so more than twice as much as stock.

For now I arbitrarily rammed the E85 table down (second shot) and will see how it goes tomorrow. But this will be a lot of experimentation, the values still seem high to me, could use some help here with approximation.

This can of course be also due to after start enrichment that I have not touched yet, it is stock for both fuels, perhaps it is not overfueled in cranking, but undefueled in afterstart. What do you think?
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prj
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« Reply #213 on: May 17, 2018, 02:49:48 PM »

You can't blend 1:1 between the tables, they are not linear, you need a table for a blending factor.
Same with ignition timing, need a separate table for factor based on ethanol percentage.

They are not excessive, because ethanol does not evaporate easily, only the gasoline portion evaporates.
So basically you're washing fuel down the bores really hard on cold start with ethanol. On E70 you need 3x as much enrichment as on gasoline on crank when really cold and so on...
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woj
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« Reply #214 on: May 17, 2018, 03:17:02 PM »

They (the cranking tables) were lineary blended on the Saab bin I think, but I'd have to double check that. For ignition and boost I do have a kline factor for blending the two tables (following your earlier hint in the other thread Wink), but these are so far just stock for both fuels. The code fix is easy then, but it still does not tell me what the kline for fkstt this should be.

OK, but 3x enrichment for E70 on freezing temperatures does not scale (in my mind) to effective 2+x scaling I got for rather warm start ups on E20, so at least in the upper part of the table that is now applicable for me, the values are too high, kline or uniform blending, no matter.
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jcsbanks
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« Reply #215 on: May 17, 2018, 06:52:17 PM »

If you have available flash for the tables and code, and RAM for a few variables, if you are not doing and instead using linear equations, like prj recommends I would make tables for blending. I use three for fuel, ignition and load. You could share ignition and load perhaps, but on my target engines they have different needs where you may have very gentle ignition retard after reaching MBT with increasing ethanol content due to the faster flame speed of ethanol, but steeper drop in max engine load due to running out of pump on engines with a single DI pump.
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prj
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« Reply #216 on: May 18, 2018, 12:34:36 AM »

Linear blending does not work on Ethanol for cold start, end of story.
I highly doubt it is done that way in any OEM bin.
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woj
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« Reply #217 on: May 18, 2018, 01:07:06 AM »

Well, actually I have been just now rechecking the Saab maps, it is far more complex than just non-linear blending. For E85 it seems the cranking injection times are done in varying pulses depending on the temperature and number of combustion cycles. Eg. when very cold it actually first does less injection (50%) for 4 combustions, then scales it up to 200%, while on warm first two injections are at 200% and the rest at 100%. I still do not see a scaling map for blending there, but the whole stuff is hardly penetrable, and I am guessing this blending is hidden in all the maps like the one I have seen. All E85 treatment there seems to be much more complex than one would expect.

I still do not have any answer to my initial question though - put blending method aside - the actual E85 cranking factors or the scaling distribution between 95 and E85 ("3x at very cold" does not cut it). For now I looked at my first map (and even the second one I made) and realised it is totally inconsistent, adds 3.8 times more fuel at -15, 7+x more fuel at 0, and then 4x more fuel at 20. That is essentially crap, should have noticed it earlier. Today's morning start with tuned down table was better, but still choked. Will sort it out experimentally for my E22, this will give me at least one scaling point for the non-linear blending.

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woj
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« Reply #218 on: May 18, 2018, 04:15:55 AM »

This is going to be a nightmare to get right under these conditions. My first map was overfueled, but the problem lies elsewhere, the choke is due to throttle closing, just did a quick log (engine temp 30*C). This was done with stock FKSTT, fuel is E22. The startup reaches 1200 rpm nicely, then the ECU decides this is too much and aggressively rams it down. Now that I think of it I get occasional things like this also on stock maps / fuel, it has something to do with throttle adaptation, and this gets reset each time I flash I believe. So getting the fkstt factors right is one thing, the other one is to be patient enough for the ECU to finds its ways. Possibly there is a way to reduce the throttle reaction instead, have to look into this. And yes, I know that the cranking fuel will also affect the reached start rpms...
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woj
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« Reply #219 on: May 18, 2018, 12:48:09 PM »

Found some information of the sort I was looking for:

http://www.ft86club.com/forums/showthread.php?t=94751&page=5

Though totally different technology / cars, there are some numbers that I was expecting to see. I cannot see them mentioning non-linear blending for cranking fuel (but I did not read through the whole thread), yet they only have sensibly looking values down to only 10*C, clearly it's a warm climate down there. But that's what I am looking for at the moment, will not be colder here that 10*C for a good few months. Ball parked my maps based on these and also added non-linear blending scale to play with later on when it gets colder.
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