Another E92 Mystery Timing Pull

I just got my unlocked TCM installed and I have corrected to the proper WOT MPH shift points so now I don't shift early on the WOT 1-2. However, this has caused it to read certain operating conditions to make some weird timing pull. I can see the "Torque Management Advance" pull 12.3 degrees of timing at 6100rpm. I know its not a predicted torque situation since throttle remains at 100%, and therefore, from at least my understanding of the way the E92 works, is this isn't a problem caused by a low driver demand torque value. I am running E85 and have a ported intake and throttle body, so I should be getting a little more airflow than stock, but my tune remains mostly stock, but I have tried upping the driver demand although I know this isn't a good practice.

At first this issue looks like its similar to what WS6FirebirdTA00 was talking about in a similar thread below, but I think mine is something else since you can see there is no change in torque sources for immediate or predicted, immediate torque source just stays at "none".


I think this could be due to some random E85 thing that's caused by tables we don't have access to.Attachment 86174Attachment 86175Attachment 86176

Thanks for the help

TMA could be for multiple reasons. Are you sure you're not spinning the tires? Anyhow, post the tune and the log file if you want help.

I don't believe its spinning, but I didn't log driven and undriven wheel speed to confirm. I wish all the torques made more since, I can see the TCS torque request at -625ftlbs then jump positive. Now if the "Traction Control Torque" is an actual meaningful PID and it represents maybe a percentage of full torque?? then yes I guess it could be a traction control event. You can see the traction control desired torque go from 100% to 0% then a few frames later the predicted torque source changes from "RPM Limit" to "Axle". Which kind of makes sense, since in the run I launched with launch control so maybe it was trying to limit RPM using predicted torque control at 2200rpms for the launch, then it never got another predicted torque request. Its so weird that it can pull 12.3 degrees of timing due to TMA, then the immediate engine torque source be "none".

As a side note, I am going to assume that when the immediate engine torque source is "none" then timing is referenced from strictly from the base main timing table, and the ECM is not trying to achieve a target torque by using anything including timing, cam advance, etc.
Attachment 86219Attachment 86220Attachment 86221
So I thought the tune and log file posted in my original post? I attached my log, tune, and tcm tune again. Thanks TriPinTaZ you always seem willing to help everyone. If I only had my own shop and engine dyno maybe I could actually get things to work and figure some stuff out, this stuff is just so frustrating since we are basically just having to guess and check.

With the predicted torque settings, it doesn't just pull throttle, but also spark.

On an LT4 set up, tune was dialed in perfect with no pull in either, but once E85 was added spark was being pulled from the engine similar to what was happening above. Keep adjusting your tables.

Thanks for the info! What tables are you recommending to adjust? I tried adjusting the torque coefficients for E85 about 10% higher following the same difference the flex fuel 5.3 has, and I have also tried leaving them alone. My stock tune has them the same, but then again the LT1 was never meant to be flex fuel.

You changed the coefficients by 10%? Or you properly edited the torque table with the virtual editor?

I edited the torque tables by 10%, then calculated coefficients. Does anyone know how the traction control torque works? I'm assuming its a percentage of full torque, so if its at 75%, its targeting whatever the virtual torque coefficients calculate for that airflow, rpm, etc. multiplied by .75?

Also it looks like a traction control event isn't reported on the "torque source" PIDs, and if there is a traction control torque reduction its counted as "Axel"?

If this is true that TCS is reported as a percentage of full torque, that I am never getting full torque, since it never goes to 100% at WOT when I know I'm not spinning. The TCS desired torque and TCS requested torque don't make sense either since they just sit at 640, and 879 ftlbs.


I guess I need to keep in mind that I'm in "Stabilitrac Competitive Mode" so who knows what kind of torque reduction requests are going on considering the fact I think that TCS calculations are done in a module that's not the ECM or TCM, maybe CCM or BCM?? I really wish we had access to tune TCS and launch control, I think we could make it really useful if we could tune out the over aggressiveness of it.

Also as a side note, does anyone know what causes RPMs to actually decrease, at WOT in first gear right before the shift I can see noise of say +/-50rpm, where RPM is rising then it will decrease? Physically I know there's no way its actually happening, and this is before any pressure is commanded for the on-coming clutch in the transmission.

if you just go into the minimum base timing and raise that table you can make it go away without a bunch of other adjustments if this is the only goal.My zl1 was pulling a lot of timing on the shifts after I got the throttle to stay open so once I set both minimum timing tables to around 10 degrees at shift points it stopped to large timing pulls. I still get a little but im ok with it dipping the torque a little on a car thats making this kind of power I feel it it throws everything it has at the trans it might not like it. Im seeing around 12 degrees now vrs -20 on the shifts so not losing a ton off total timing. At this point it isnt noticeable and still pulls through the shifts with out that hitch or back step they do stock.. Do both minimum spark base and long term at your shift points.

Also after looking at that screen shot the timing dip before the shift can be the soft touch rev limit becoming active too early. I had my zl1 doing that also it would drop the throttle to 40 percent on the 4-5 shift as it got too close to the 6800 redline I had set. I moved my shift rpm down just a little 50 rpm and I zeroed the accel threshold table and turned off use predicted torque under fuel>cutoff /dfco> control method.

Thanks for the tip, and I was thinking the same thing:

Attachment 86471

Except I only did it to the specific range I am seeing timing drop (.8-.9 airmass and 6000-6300rpms) hoping that it will still allow a legitimate torque reduction when I need it like protection during shifts.



I was also reading another thread on here about the way the modern TCMs control clutch to clutch shifting. Apparently there is a initial phase at the start of the shift where engine RPM will remain constant, this is where the off-going clutch is reduced at about the same rate the on-coming clutch is increased. At the end of this phase, both clutches will still be slipping, but the on-coming clutch will have assumed control of torque through it, this happens precisely enough (off-going decreases at the same rate on-coming increases, accounting for clutch torque capacities) to where RPM remains relatively constant. The next phase of the shift is what the driver usually feels and you actually see on the tachometer, and also is where the majority of torque reduction comes in, since you get a pseudo torque increase from the momentum stored in the engine and rotating components going from a high rpm to low rpm, the engine decreases torque to keep the delivered torque constant because of the pseudo torque created.

Anyway at high rpm before the shift you can see this. On the logs you can see "Trans Slip RPM" jump up, the "On/Off-Going Clutch" PID changes, but the engine hasn't dropped RPM at all, it is just kind of hanging and you see a lot of noise, up and down. I haven't looked close enough at the trans pressures PID to confirm this theory, but to me it makes sense especially since you see the trans slip PID jump up.