Topic: Does the ECU learn down? Debate about it here.

[kennysabarese]

Honestly, I think if the computer system is open and simple, it's a lot easier than having to do points and plugs and adjust carb jets to get the right AF ratio.

But if you really wanna go low tech, get one of these.

http://www.jegs.com/i/GM-Performance/809/19201333/10002/-1?parentProductId=1192223

[kennysabarese]

MY questions is............DOES KELU NEED HIS ENGINE TO "LEARN" AFTER A "RE-FLASH" BEFORE HE USES HIS NITROUS ON A 1/4 MILE RACE?


Most members say, that he needs to have his ecm "learn" first and do some runs................before he race?

why?

My theory is that he will make better power after he drives it a bit after changing the tune.

[SKY888]

My theory is that he will make better power after he drives it a bit after changing the tune.

so basically your theory is saying that, on my last dyno tune run which I get 403whp last year (since it was re-flashed before that run)...................a few runs on the street.....if I go back to the dyno a week later.....I'll get more peak power?

[kennysabarese]

yes that is my theory. and I think Tazz would agree.

[SKY888]

hmmmm...interesting.........

[Arabas]

to reply to the title of the topic, No, i don't think from my experience so far that the tuned ECU learns down.
to answer to the other question, that is if the ECU adjusts to a new tune, i say Yes, it definitely needs a few runs to adjust.
let me explain myself with an example.

i recenlty got Vince to send me a tune, which was: Cruise button off the tune i had been using for the last 4 months and when cruise button on a tune he had send me that felt much more brutal, higher torque form lower rpm, like a kick in th a$$ (in the cruise on, Vince usually sets a tune similar to the factory for the times you just want to cruise, but he was kind enough to try this for me).

so now, i have two tunes loaded and no OEM-like.

when i first flashed this tune in my ecm 1 month ago, i tried the "cruise off" tune and it felt good, just a little bit less powerful than the same tune i had previously loaded. after some miles and some hard accelerations it felt fine. now after a month, it feels exaclty the same.
now, 1 month ago that i loaded this tune, i also tried the "cruise on" tune which feels much more brutal.
at the first acceleration with 4th gear i had some knock and i got dissapointed. but then i did some carefull accelerations (always watching out for knock) and after a few runs, the car drove perfectly but not with the power i was expecting. now, after a month, the car drives as i expected it would. same has happened with other GT buddies.

so my conclusion-assumption is that yes the car needs some time to adjust some parameters to run great (knock, good hp and torque etc).
If Kelu tries a select a tune method, then he can do some trials with the nitrous tune and by the time he gets on track, the car will be great and adjusted to perform its best.

[Kagem]

Along with Arab, yes i'd say the same. I've change 5 tunes till now and every time the car performed better and better every after run, until after a while it adjusted to where it should be. In my opinion Kelu must have some trial runs with the nitrous before he goes and bites the chicken, good luck Kelu....

[Dave@DDMworks]

Short answer - depends on the tune

long answer - The ecm runs on a torque based/load parameter for peak power. This is an adjustable parameter in the ecm that tells the ecm how much calculated torque the engine should produce. The ecm then uses several sensors to help it determine the torque that it is producing and it adjusts different parameters of the engine to hit that calculated torque figure. On a stock car this is why we would see that after making modifications to the car, without changing the ecm calibration after several drive cycles the power would come back down to stock power levels, as the ecm will adjust boost pressure and timing to lower the output of the engine until it hits the target torque figure in the calibration. In this case the ecm will learn down.

Now that we have gained the ability to change the calibration of the LNF ecm we are able to change this target torque figure to something much higher than stock. Once we do that the ecm is trying to reach a figure that is much higher and therefore changes boost pressure to hit this higher calculated torque number. Also there is base timing that comes into play. When you put a car on the dyno and run the car and datalog it, depending on who did the tune on some of the initial runs you may see some knock retard which will decrease during each run until it disappears, once again depending on who did the tune (as a side note, some tunes can be overly aggressive with the timing and never get out of having some knock). Some small amounts of knock on the tune when first flashed in (less than 4 on HPtuners, especially on initial tip in) is not that bad. As then the ECm starts to adjust timing at those points to reduce the timing so that there is not any knock. As Kenny mentioned earlier though, the ecm will keep trying to add timing back at those points while driving to try to reach the timing that is in the calibration though, that is if that timing is higher than what it is running. If the timing that is put in calibration is low enough to not cause any knock then the ecm will not pull any timing and also will not try to go any higher then what is in the calibration.

(as a side note here about boost pressures - the above paragraph explains why we really do not care about boost pressures with the LNF. A lot of people are still stuck on the old mentality of boost controllers that were set to a specific boost pressure and by raising that pressure, more power was made. With the LNF you have to forget that and instead focus on calculated torque and realize that the ecm is going to run whatever pressure it needs to run in order to hit that torque number. In the end all boost pressure is not a good thing, boost pressure is the measurement of restriction to flow in the engine. If you can produce 300ft/lbs with 21psi that is much better than producing the same 300ft/lbs and having to run 30psi. The boost pressure on these motors is controlled by the ecm and is changed to produce the calculated torque the ecm is calling for nothing else. Make the system more efficient and you can make more power with lower boost pressures, which produces less heat and less stress on the turbo charger and motor.)

When the ecm has to pull timing because of knock it pulls more timing then what is needed to prevent the knock in the first place. For instance if you are commanding 10 degrees and there is knock, the ecm may pull timing back to 6 degrees of timing, reducing power. However the car may run fine without knock at 8 degrees of timing. So by having knock and having the ecm pull timing you are losing some power. This is why the car can run stronger with more driving, as once the ecm learns down to the run only 8 degrees of timing, you will have more power then when it was having knock and lowering the timing down to 6 degrees. However in this case if the timing is set to 10 degrees the ecm will try to go back up to that value in the calibration over time. So in this instance the ecm is learning down and up

As for fuel trims, those are used by the ecm to adjust fueling to hit whatever target is in the calibration. The short term fuel trims are small corrections made by the ecm very quickly and the long term trims are made by the ecm very slowly. The fuel trims are good for adjusting to weather changes but should end up being around +/- 5% after driving the car for a little bit. They really do not have any effect on power, unless the fueling is way off and the car is running very rich or very lean on the initial tune and the ecm has to add a bunch or take away a bunch of fuel to hit target air fuel ratios.

So what is programmed in the tune determines if the the ecm is going to learn up, down or not at all.

[kennysabarese]

Strange because 888 is saying he gets more KR over time... you are saying he should get less.

[SKY888]

DDM dave..........so what seems to be different in my tune compared to others?  Howcome I'm observing less KRs after a RE-FLASH? 

[Dave@DDMworks]

DDM dave..........so what seems to be different in my tune compared to others?  Howcome I'm observing less KRs after a RE-FLASH? 

Without a datalog of your runs right after a flash and then after several runs it would be hard to say. The first thing I could think of would be that the MAF scaling is not correct on your tune and the fuel mixture right after the flash is a proper air/fuel ratio for your car to run properly, but as the ecm adjusts fuel trims the system leans out a little which will cause it to be prone to detonation, especially at the higher cylinder pressures you are running. Once again this is just a guess without seeing any data logs.

[SKY888]

Without a datalog of your runs right after a flash and then after several runs it would be hard to say. The first thing I could think of would be that the MAF scaling is not correct on your tune and the fuel mixture right after the flash is a proper air/fuel ratio for your car to run properly, but as the ecm adjusts fuel trims the system leans out a little which will cause it to be prone to detonation, especially at the higher cylinder pressures you are running. Once again this is just a guess without seeing any data logs.

thanks Dave,

but the thing is, there's no detonation during higher RPMs.

those KRs I observed are very obvious on low rpm range only.........especially on an uphill climb.....

[Dave@DDMworks]

thanks Dave,

but the thing is, there's no detonation during higher RPMs.

those KRs I observed are very obvious on low rpm range only.........especially on an uphill climb.....

The lower rpm's is when the pistons speeds on the engine are low and depending on several different factors, the flame front of the burn has more time to be able to spread all the way across the piston and generate peak pressure. Also going uphill you are putting a higher load on the engine. If this peak pressure is developed before the engine reaches TDC then the force on the piston is trying to push the crank in reverse and we can see engine knock. The flame front speed is also dependent on fuel ratio, so that is why I am leaning toward a fuel trim situation causing your knock, but without a datalog, that is just a guess.

As the engine speed increases, the flame front has less and less time to get across the piston and develop peak pressure, that is why you advance timing more and more as engine speed increases. Otherwise your peak pressures come so far after TDC that the peak pressures are low and you do not produce as much force on the crank.

[SKY888]

gotcha!  thanks for the elaborate explanation Dave.

Car is not running right now, and at the shop for upgrades.

Once I get it, I'll try to do some before and after data logs.........and see what's going on.......

[Gentleman Jack]

DDM Dave,

I've never understood the issue better than after reading your post.  Then Kenny posted and I got confused again.

Thanks for taking the time.  Also, thanks for the responses on the P2237 issue as well.  I am picking up the part on the way home from work today.

GJ

[LatinVenom]

This is the reason my Upgraded Wheel with the DDM tune runs so well.

[snaponbob]

So is that what I'm seeing with my tune? I can push my tune back to the car. Then it responds well,  seems to spool faster and has less lag. After drivingin it back and forth to work for a few weeks, I've noticed that it doesn't spool as soon and it seems to be, well just sluggish until I repush the tune? If I go out and rail on it on the way home, the next day it seems like its got all that pep again.

Whose tune is it?

[Gentleman Jack]

Whether its phantom power or real power, I notice the same thing with the tune.  It's the same with all three of the different tuners I have had.

[shabby]

So is that what I'm seeing with my tune? I can push my tune back to the car. Then it responds well,  seems to spool faster and has less lag. After drivingin it back and forth to work for a few weeks, I've noticed that it doesn't spool as soon and it seems to be, well just sluggish until I repush the tune? If I go out and rail on it on the way home, the next day it seems like its got all that pep again.

Whether its phantom power or real power, I notice the same thing with the tune.  It's the same with all three of the different tuners I have had.

After you flash a new tune and floor it the first couple times the ecm adjusts the boost to the set boost level in the tune, obviously its going to overshoot the boost the first couple times until it learns, that's what you guys are feeling. Everything is in the tune, if you want it to feel like the first time you floored it you have to make those those changes in the tune.

[kennysabarese]

Will that fit in '08?

No clue