Pedal position vs. commanded TAC position weirdness

[gmtech16450yz]

Has anyone logged actual pedal position vs. actual throttle position enough to notice anything weird on these E38's? I've been trying to figure out why the correlation between pedal and throttle vary between two distinctly different modes. Most of the time the throttle will open ahead of the actual pedal position, which makes acceleration feel stronger since your foot isn't pushing down more, but the throttle is still opening more. Stock trucks do this normally. (I'm talking about E38's in 5.3, 6.0 and 6.2 trucks and SUV's.)

The other mode, which seems to come and go at random times, is that the throttle will stay tracking pedal position, without the throttle opening faster and more than the actual pedal movement. When it goes into this mode (I call it low throttle mode) it will stay that way all day. It almost always goes back to normal the next day. It might not do it again for a few weeks. It has nothing to do with the actual tune, it will switch back and forth between these two modes on the same tune. (Meaning it's not something I change in a tune, it goes back and forth in between tune changes.)

My guess is there are some parameters that we don't have access to that affect the relationship between pedal position and throttle position. I wish I could figure this out, there is a huge difference in the feel of the power when it's in this "low throttle" mode. I can tell it's doing it as soon as I start driving, it just feels a little "flat" compared to when the throttle is advancing ahead of the pedal. I believe what I'm trying to describe is the equivalent of the throttle cracker and follower in the older LS1's?

Thanks guys, hopefully someone has seen this. If I get a chance later I'll try to post up a screen shot of the logs that show the difference.

[gmtech16450yz]

Here's the screen shots...

I'm betting the only guys that even noticed this on other E38 are the ones that have a lot of logs with pedal position and TPS (either commanded or actual, doesn't matter) logged.

The interesting thing here is that if you're trying to tune or assess changes and this happens you'd think whatever change you made lost power, when actually it had nothing to do with what you changed in the tune. Have any of you truck owners ever started driving one day and thought "Hmm, this thing just doesn't seem as strong today", but not enough to make you really think something is wrong? Anyone tuning a car or truck with ETC (throttle, not traction) should be logging these two pids so you can really see what's happening between your foot and the throttle.

Here's a couple screen shots of what's happening, hope they're big enough to see, I didn't want to make the images huge but I might have to if it's too hard to see. All you have to do is look at ACC (pedal position) and TAC (commanded throttle position) and you'll see what I'm talking about. Normally you'll see something like the 23% pedal position resulting in 38% throttle position, this is what a stock tune would even look like. In this "low throttle" mode, you won't get the throttle advancing farther than the pedal, actually it's behind pedal movement if you take into account the fact the throttle doesn't go to zero like the pedal percentage does. In the "low throttle" jpeg (bottom image) the ACC is at 38% and the TAC is also at around 38%. This results in kind of a slightly "dead" power feel, even though you've done nothing to actually change the power, it's just how much more the throttle is opening ahead of pedal position.

Obviously if this can be figured out, or if someone already has the answers to this, wouldn't it be awesome to actually be able to change the mapping of pedal vs. throttle? All I want is to keep my truck from going into this "low throttle" mode.

Thanks guys, sorry for the long post.

http://i841.photobucket.com/albums/zz337/j16450yz/normal-throttle.jpg

http://i841.photobucket.com/albums/zz337/j16450yz/low-throttle.jpg

[GAMEOVER]

This is interesting, I've felt that about my truck also. Sometimes little pedal movement gets my truck going & other days I really have to get on the throttle to get it to move (like it lost power) The craziest thing I notice is how after a cal only flash it feels really good & strong but the next day It goes into that "low throttle" mode, like you're referring to.
I always thought it had something to do with a Torque Management table that I haven't tried messing with yet...:)
I have never logged that TAC Pid...

[swingtan]

Looks somewhat like "throttle Follower" to me. In the second image, it appears that the pedal / throttle is much more stable than the first. It is possible that in the second, you have gone over the setting in B1604 ans follower has been disabled. It may be worth logging air flow at the same time to see if there is any difference there.

[gmtech16450yz]

[QUOTE] The craziest thing I notice is how after a cal only flash it feels really good & strong but the next day It goes into that "low throttle" mode, like you're referring to./QUOTE]

Yes! That is definitely one of the clues, I've also noticed that after flashing a tune, no matter what the change is, it always runs in the mode that makes the throttle advance ahead of the pedal, making it seem stronger. And yes, it will change all by itself even though you're still running on the same tune. That led me to believe it has something to do with throttle learn, and simply doing a reflash resets the learn somehow. I've also noticed that it seems to have to do with how the first cold start of the day is. If the idle is too high or too low it will effect what this "follower" does for the rest of the day. I've even thought it might have something to do with whether I jump in and go, or let it warm up for a while before starting to drive. There has to be some modifier tables or throttle learn parameters that we don't have access to that control this.

Gameover you have the same truck as I do, log that pid and see what it looks like. Log TAC_PCT and APP. If you put the APP scale at 0 to 100% and the TAC_PCT scale at 8 to 100% it will be really easy to see when it switches modes. If the TAC_PCT lines are above APP, it's in the "normal" mode, if the TAC_PCT lines are below the APP, it's in the "low throttle" mode. I set my TAC scale that way (the bottom of the scale starting at 8%) because anything below 8% is pretty much idle.

[gmtech16450yz]

Swingtan, B1604 in my tune is lower than stock (stock is 31.999), it's been that way for quite awhile. It seemed to me that B1604 had more effect on decel than accel, I had success lowering it to get the coastdown rpms to drop faster (like lessening the dashpot on a carb). Good point on going over maximums (or under minimums), sometimes these tables have hidden max values that if you go over them they don't work anymore. Oh yeah, those two screen shots are from the same tunes, I didn't do any reflashing in between.

I have noticed that you can create the same effect by playing around with B1650-Max ETC Area. If you go lower on the numbers, it makes the throttle open ahead of pedal movement since it thinks you have a smaller throttle body than stock. Opposite also has the effect of making the throttle follow pedal movement closer, since it thinks you have a huge throttle body and small movements would make bigger airflow changes.

I don't think either of these tables are the answer though, putting the settings higher or lower than stock don't seem to have an effect on this random "low throttle" mode.

Thanks guys.

[ringram]

Adaptive Abuse Management? :)

[gmtech16450yz]

Anybody figure anything out on this?

[gmtech16450yz]

Anyone find anything on this or see what I'm talking about? It seems to me that this has to do with the throttle/idle learn that the E38's do on startup. If you do a cold start up and start driving right away it won't run the idle learn, which most times will leave the relationship between pedal and throttle in the higher mode. If you do a cold start up and let it idle for a few minutes before driving, it will learn the pedal/throttle relationship lower and the throttle will not track ahead of the pedal movement.

Ross, Paul, Joecar, have you guys looked or have you seen any other tables in the E38's that have to do with throttle or idle learn? It also seems like it has to do with the computer seeing more airflow at a certain throttle position that it likes so it just scales back the relationship between pedal and throttle. I know there are DTC's that will set if it gets too far out of range, but I think it's also reducing throttle opening slightly to try to keep airflow/tps/pedal position in what it thinks is the right range.

So many guys are just looking at full throttle power, which this does not effect, I wonder how many are adding throttle response and power with their add-ons only to have the computer take it away?

Thanks

[gmtech16450yz]

Hello? Anyone out there? 4 months and not a word from any EFILive guys on this?

I own and use both EFI and HPTuners, I hands down believe EFI hardware, software and BBL is WAY better than HPT, but come on guys, at least the competition is trying to help me figure this one out.

Supposedly there are tables that control pedal to throttle mapping, and PID's that show what modes the throttle curves are in. (There are 4 or 5 throttle modes, I just have no way of knowing why it's changing modes or what mode it's changing to.) This does have to do with idle/throttle learn, if I reset idle learn with the scanner or a Tech 2 it will go back to the higher throttle mapping every time. I just can't get it to stay there consistently. (Obviously "idle learn" does more than just the idle.) If all we got was a couple PID's that showed anything about idle/throttle learn, that might help. Or any tables or on/off settings that control when it does the idle learn. Anything. Please. :)

Thanks

[GMPX]

I'm not sure about 5 throttle modes, but there is a series of tables that map the pedal position to blade opening, we don't modify them. It's a little more complex on the E38 to do that than the LS1 was (we did allow it in them).
Normally the response tables are changed by the driver, such as 'Sport Mode' etc, I don't think the ECM determines what response map it uses.

[gmtech16450yz]

Modes of Operation
Normal Mode

During the operation of the throttle actuator control (TAC) system, several modes or functions are considered normal. The following modes may be entered during normal operation:
• Minimum pedal value--At key-up the engine control module (ECM) updates the learned minimum pedal value.
• Minimum throttle position (TP) values--At key-up the ECM updates the learned minimum TP value. In order to learn the minimum TP value, the throttle blade is moved to the closed position.
• Ice break mode--If the throttle is not able to reach a predetermined minimum throttle position, the ice break mode is entered. During the ice break mode, the ECM commands the maximum pulse width several times to the throttle actuator motor in the closing direction.
• Battery saver mode--After a predetermined time without engine RPM, the ECM commands the battery saver mode. During the battery saver mode, the TAC module removes the voltage from the motor control circuits, which removes the current draw used to maintain the idle position and allows the throttle to return to the spring loaded default position.
Reduced Engine Power Mode

When the ECM detects a condition with the TAC system, the ECM may enter a reduced engine power mode. Reduced engine power may cause one or more of the following conditions:
• Acceleration limiting--The ECM will continue to use the accelerator pedal for throttle control; however, the vehicle acceleration is limited.
• Limited throttle mode--The ECM will continue to use the accelerator pedal for throttle control; however, the maximum throttle opening is limited.
• Throttle default mode--The ECM will turn off the throttle actuator motor and the throttle will return to the spring loaded default position.
• Forced idle mode--The ECM will perform the following actions:
- Limit engine speed to idle by positioning the throttle position, or by controlling the fuel and spark if the throttle is turned off.
- Ignore the accelerator pedal input.
• Engine shutdown mode--The ECM will disable fuel and de-energize the throttle actuator.

These are "failure" modes, but I think what I'm seeing is the computer putting it into "acceleration limiting" mode at times. (?) This is all GM gives us as far as an explanation of what happens, pretty vague. I have no way of knowing what they mean by "acceleration limiting", like how severe is the limiting or is it a minor step before it sets a DTC and light and shuts the pedal down all the way?

This is different than the user switchable modes you mentioned, but the computer may be using some sort of these modes automatically when it sees something it doesn't like, like too much airflow.

I don't know of any E38 cars or trucks that have a user controlled mode switch. If there was and by chance it was hard wired into the E38, that would be something I'd like to look into. Have you seen any tables or checks on when and how it does the idle learn? I'd like to be able to turn off the idle learn, I believe it would solve my "low throttle" problem and probably wouldn't have any adverse effects.

Thanks Ross.

[Highlander]

To disable idle learn zero out the correction tables for the idle section.

[gmtech16450yz]

To disable idle learn zero out the correction tables for the idle section.


Awesome! Now we're talking! Thanks Highlander. That's what I was hoping for, someone to come along and mention something I haven't tried yet. I never thought about if it never corrects, it can't "learn" what to correct to.

I have tried reducing the correction tables quite a bit, and did turn them all off when I was getting the base idle nailed down, but they've been back pretty much to stock for awhile now. Next time it gets into that "low throttle" mode I'll turn all the corrections off, do an idle learn reset and see what happens.

What about B1601 and B1602 (airflow correction coolant and baro tables)? If I left those on at least I would still have a little cold start and altitude control. Do you think it will still try to do the idle learn if those tables aren't zeroed also? I guess I could just start with everything off and if it fixes it I'll try adding back in just those tables and see if it relearns to the low throttle mode.

Thanks again, I'll let you know if that does it.

[gmtech16450yz]

Oh well, so much for that idea.

Zeroed out all idle correction tables and the "low throttle" mode popped back up after a couple days. Dammit I wish we had access to whatever controls the pedal/throttle mapping. Or I wish I could figure out what the ECM sees that it doesn't like to put it in this mode. Same tune, a couple days driving, maybe a dozen logs and it will be in "low throttle" mode once or twice with no rhyme or reason why. It will stay in whatever mode it's in during the entire trip or log, it has never switched from "normal" to "low throttle" mode in the middle of a log. It's "learning" or switching into this mode on start-up. Why dammit?!

Ok, here's an idea, I will PayPal $100 to the first person that nails this for me. Tell me why it does it, what to turn off or on to stop it from doing it, or provide me (us) with the tables to control this. (Ross, Paul?) Basically help me figure out how to keep my truck from going into this "low throttle" mode and I'll send you $100.

Thanks