2017 Camaro ZL1 engine overpowers braking

[ZLRob]

I know I'm not the only one who experiences this, but has anyone else currently or in the past actually experienced this issue and found a solution for it (ie is it a tuning issue, is it a stock throttle body airflow issue, or maybe is it even both)? I have searched and searched deep and don't come across any clear cut answers so here I am now.

This is the way it feels for me coming to a stop:

If I'm revving up to come to a stop (it feels more prevalent in paddleshift mode once I've downshifted to first gear) everything feels fine up until I come to the light or stop sign, then suddenly as the RPM is coming down on the lower end, I feel the engine wants to somehow overpower my braking then I have to step on the brake harder to override that unfavorable engine behavior. I have really looked at it and do not notice the RPM rising as it occurs, but it definitely feels like some sort of engine torque management issue or something.

Anyone got anything? HP Tuners parameters of interest perhaps? Thanks guys.

[Tunercharged]

Just have to log everything that could cause it there, timing, air mass per cyl. Or just lower timing in high octane table a little for your idle speed as an initial try.

[ZLRob]

Just have to log everything that could cause it there, timing, air mass per cyl. Or just lower timing in high octane table a little for your idle speed as an initial try.

You know what, I found it. It is weird. It's almost like there is indeed a sudden timing spike upwards and with that timing spike it induces a sudden lean spike all the way up to 14.5- 14.8% LTFT when coming down to a stop. I'll attach some screenshots at what I'm looking at. Notice I am in 1st gear and at a very low speed when this happens.

Attachment 124840

Attachment 124841

Attachment 124842

I revised the timing map but I am not seeing where or why it would suddenly induce the sudden spike in timing at all.

[ZLRob]

I may have found the issue. I am noticing 6.3 degrees of variable cam timing while this is occurring which eventually steps down to 4.7 degrees after the timing and lean spike event occurs. I looked and found the VCP spark table is the only thing that could be adding timing outside the high octane table. Could this be the cause of it?

Attachment 124844

[TriPinTaZ]

Are you logging torque management advance? What about Driver Demand Commanded Torque, and other Torque PIDs?

Typically the reason for spark to jump like that would be if torque commanded spiked....which could be many reasons.


Post your tune and Log, although your log may be missing important PID's to help.

[ZLRob]

Are you logging torque management advance? What about Driver Demand Commanded Torque, and other Torque PIDs?

Typically the reason for spark to jump like that would be if torque commanded spiked....which could be many reasons.


Post your tune and Log, although your log may be missing important PID's to help.

I am, but not graphing it. I do see an advance of 30.5% when that occurs but it doesn't seem to be affecting it because it stays around that advance even while it's not doing it. I can add those PID's, however and run a log though given how predictably easy it is to duplicate.

Any other PIDs you recommend here? I have added the TQ managment on the graphing side as well as driver demand torque percentage.

[TriPinTaZ]

Screenshots aren't going to cut it if you want help. Post tune and log. If you don't want it to be public, email it to me and I'll see if anything stands out.

There are quite a few torque PID's that are helpful. There are threads on what is helpful. Pretty sure I have a list in one of them too.

[ZLRob]

Screenshots aren't going to cut it if you want help. Post tune and log. If you don't want it to be public, email it to me and I'll see if anything stands out.

There are quite a few torque PID's that are helpful. There are threads on what is helpful. Pretty sure I have a list in one of them too.

Sent to you over email. Thanks for offering to take a look at it for me because this one has me scratching my head. Torque Management sucks. Haha.

[itspeat]

When I first tried tuning SD with the MAF disabled, I had an area where the numbers were slightly off. The result was, when decelerating, the requested torque would be negative... then around 2k RPM the car would maintain speed.... almost like cruise control was on.
I looked at the torque and it was requesting a positive value. Just enough to maintain speed, I had to tap the brakes to get out of that area of the map and then the car would decelerate as usual.


Another time, in the very beginning, I also accidentally uploaded a tune with calculated coefficients for the VVE table with an entire zone completely messed up. The zone was way higher than the others.
I went to pull out of the parking lot and it hit that zone and it tried to ask for like 900ftlbs of torque at 1,300RPM. Scared the crap out of me lol.


bad VVE Zone.png


torqueJump.png

[ZLRob]

When I first tried tuning SD with the MAF disabled, I had an area where the numbers were slightly off. The result was, when decelerating, the requested torque would be negative... then around 2k RPM the car would maintain speed.... almost like cruise control was on.
I looked at the torque and it was requesting a positive value. Just enough to maintain speed, I had to tap the brakes to get out of that area of the map and then the car would decelerate as usual.


Another time, in the very beginning, I also accidentally uploaded a tune with calculated coefficients for the VVE table with an entire zone completely messed up. The zone was way higher than the others.
I went to pull out of the parking lot and it hit that zone and it tried to ask for like 900ftlbs of torque at 1,300RPM. Scared the crap out of me lol.


bad VVE Zone.png


torqueJump.png

Are you suggesting that the issue lies somewhere within the VTT's? If so, given the things tried already by myself, Jason, and another tuner, I wouldn't be surprised if that answer is a yes at this point because I feel like this is where the issue is leaning into. Either that or a re- cal of the TCM which will require full T87A unlock.

Did you ever find a resolution for your issue? I'm going to assume you have a Camaro which gives you the same BS issue mine does for me right?

[TriPinTaZ]

Are you suggesting that the issue lies somewhere within the VTT's? If so, given the things tried already by myself, Jason, and another tuner, I wouldn't be surprised if that answer is a yes at this point because I feel like this is where the issue is leaning into. Either that or a re- cal of the TCM which will require full T87A unlock.

Did you ever find a resolution for your issue? I'm going to assume you have a Camaro which gives you the same BS issue mine does for me right?

The file that you sent me had stock Virtual Torque Values so I don't see that as the issue. Also, as I said in the email, your MAF values do not seem correct for a stock intake box with a drop in filter. The values are lower everywhere vs stock and MAF values are directly involved in calculated torque. This COULD be causing the car to think its making less torque everywhere so that when its coasting it is just enough to think its not making the requested torque that it should so it opens the throttle and adds timing. Try putting STOCK MAF values in below 6500Hz or so.

[ZLRob]

The file that you sent me had stock Virtual Torque Values so I don't see that as the issue. Also, as I said in the email, your MAF values do not seem correct for a stock intake box with a drop in filter. The values are lower everywhere vs stock and MAF values are directly involved in calculated torque. This COULD be causing the car to think its making less torque everywhere so that when its coasting it is just enough to think its not making the requested torque that it should so it opens the throttle and adds timing. Try putting STOCK MAF values in below 6500Hz or so.

I remember you mentioning that but given the issue has been happening well before that makes it seem really unlikely that setting the values back to OE on the lower scale of it's range will fix anything. The only reason they have been touched is due to that 5% pulley and E55 but I'm not an expert on the range values for the MAF so I won't pretend to know exactly why they were changed down low to be lower than OE values.

The thing is this has been an issue since I first bought the car and even touched it tune wise. I thought it was normal behavior but after a while I realized it was not.

[TriPinTaZ]

Typically you add fuel. But if your fuel trims aren't trying to add fuel, then it should be ok.


By the way, I see you have split pulse fueling at idle enabled. This is usually disabled. Any reason you have it enabled?

[ZLRob]

Typically you add fuel. But if your fuel trims aren't trying to add fuel, then it should be ok.


By the way, I see you have split pulse fueling at idle enabled. This is usually disabled. Any reason you have it enabled?

I think I may have fat fingered it (and by that I mean fat finger clicked) on accident. I re- disabled it on my original stable file.

[TriPinTaZ]

Literally nothing else makes sense for your issue. It doesn't hurt to try the MAF table out and see what happens with the stock curve. Just don't go WOT. What's the worst that can happen? You have to flash it back? lol

If that doesn't help then I believe you have a mechanical issue, meaning issue not caused by the tune. Having experience with the A8/A10 ZL1's, I can say they do tend to push a little, especially if you drive a manual like myself. I noticed it immediately, but it never did what your car is doing by adding timing very abruptly when coming to a stop.

Maybe verify you have the stock throttle body, its not sticking, the motor is functioning properly, and then try the throttle relearn procedure with VCM scanner?

[ZLRob]

Literally nothing else makes sense for your issue. It doesn't hurt to try the MAF table out and see what happens with the stock curve. Just don't go WOT. What's the worst that can happen? You have to flash it back? lol

If that doesn't help then I believe you have a mechanical issue, meaning issue not caused by the tune. Having experience with the A8/A10 ZL1's, I can say they do tend to push a little, especially if you drive a manual like myself. I noticed it immediately, but it never did what your car is doing by adding timing very abruptly when coming to a stop.

Maybe verify you have the stock throttle body, its not sticking, the motor is functioning properly, and then try the throttle relearn procedure with VCM scanner?

Well no, even with stock MAF values the issue would occur. Like it didn't matter if the MAF was altered or not.

That's probably not a bad idea you know that.

I don't understand why GM would allow these engines to push a little on decel though, to the point where it is potentially dangerous. You mentioned that yours does it too and that they all push a little. I have owned many cars through my life and have never once encountered one that does it to this degree while you are off the throttle. I'll try a throttle release, maybe even pull the TB and give it a solid cleaning (that is a potential factor given the car has 33K on it).

[itspeat]

What ever happened after you changed the VCP spark table? Or did you not zero that 0.16 row out?

[ZLRob]

What ever happened after you changed the VCP spark table? Or did you not zero that 0.16 row out?

I never touched it because I determined that the issue is actually originating from a Torque Management timing spike when the event occurs. There has still been no resolution to it yet though.

[ZLRob]

Literally nothing else makes sense for your issue. It doesn't hurt to try the MAF table out and see what happens with the stock curve. Just don't go WOT. What's the worst that can happen? You have to flash it back? lol

If that doesn't help then I believe you have a mechanical issue, meaning issue not caused by the tune. Having experience with the A8/A10 ZL1's, I can say they do tend to push a little, especially if you drive a manual like myself. I noticed it immediately, but it never did what your car is doing by adding timing very abruptly when coming to a stop.

Maybe verify you have the stock throttle body, its not sticking, the motor is functioning properly, and then try the throttle relearn procedure with VCM scanner?

What ever happened after you changed the VCP spark table? Or did you not zero that 0.16 row out?

I just wanted to update this and say that I FINALLY resolved this issue after a day and a half of modifying my tune, flashing, rinse, and repeat. Taz and itspeat, the issue lies within the virtual torque tables which need modification in the low RPM range. Mine were bunk from the factory or something (and I get the feeling my tune file wasn't the only one released that way). After I swapped my cam the issue stuck around. It was only until a buddy and I really started deep diving into the log outside of WOT tuning that we found the issue. TQ management interferes too much and the closer you can get it to 0 at idle (obviously it's not a perfect world when it comes to those damn tables) the less interference you get from it, the less the engine will want to overpower the brakes and behave like a normal vehicle coasting down to a stop.

[motorhead74]

Try relearning brake pedal position sensor. I have had learned values go out when tuning.