4L80E - Gen 3 ? Inconsistent in Executing 1>2 Shift

Printable View

07-01-2020
AndyGrove

4 Attachment(s)

4L80E - Gen 3 ? Inconsistent in Executing 1>2 Shift

The issue Im trying to solve is inconsistent 1>2 shift execution under WOT w/ gear selector in Drive (3rd).

1st gear holds fine, 2nd gear holds fine, all gears shift fine and feel good under normal cruising or part throttle, there are no DTCs, etc. From looking at my data, it appears to me that its not commanding the 1>2 shift according to the speed/rpms I have set in the calibration. I have not run into this issue before.. but as of today I made 8 WOT pulls through 1st to 2nd, and it failed to shift out of first on 6 of them. For the two times that it did shift out of 1st under WOT, the shift was firm and scratched the tires? felt really really good. The application is a C10 w/ a turboed 6L @12 psi boost, with a freshly built 4L80E (Jakes stage 2 kit w/ 500 miles on it) and Gen3 ECU tuned w/ HP Tuners. I have been tuning for the past few months, working my way up in boost pressure, and just today came across this issue for the first time. I have looked at the calibration and the recordings/logs from today, though I don?t see a whole lot of transmission parameters to choose from, and I have been unable to determine what my issue is.

The parameter that I have been looking at to determine if the PCM is commanding the shift to 2nd gear is [TransCurrentGear]. My assumption is that this is the ?Commanded? Gear??? Meaning, when this changes from 1 to 2, it means that the PCM has commanded the 2nd gear shift to start... Is that correct? What Im seeing is that this stays at 1 all throughout 1st gear until hitting the rev limiter, though I have my tables to shift at 5900 RPM and 61 mph setpoints. If this speed seems high to you, it is because I have 3.08 gears and a stock (tight) converter. I have verified my [Vehicle Speed] is correct and matches a GPS.

I have attached my tune, as well as three recordings/logs from today. A summary of the logs are as follows:

- 1to2ShiftSuccessful_1Jul
* 1 to 2 Shift is successful however occurred later than normal (around 6200) when normally it takes place (around 6000)

- 1to2ShiftUnsuccessful_1Jul
* 1 to 2 Shift is unsuccessful. As you can see, the [TransCurrentGear] remains at 1 until hitting rev limiter at 6400 rpm

- 1to2ShiftUnsuccessful_2_1Jul
* 1 to 2 Shirt is unsuccessful. Something unique about this recording is that if you watch the [TransCurrentGear] it bounces back and forth from 1 to 2 and right away back to 1 prior to hitting the rev limiter.

I did some forum searches and most of what I returned was mechanical. This smells more of a software/calibration issue to me, as the thing shifts great and on time when not in WOT, and if it does actually shift to 2nd under WOT, the shift feels short/firm. And as mentioned before, 2nd gear holds great at WOT, once its actually in 2nd gear.

Im at a loss of what to try next, or if there is additional parameters that I need to be looking at to figure out the issues. Any and all help would be greatly appreciated.
07-02-2020
Hondaeater

I see the rpm is about 5800 at 60 mph. This should match your WOT setting. Also the WOT enable is set low. If that is what you want.... the normal and WOT tables should have the same speeds for consistency EX.78%+ = 61mph not 39.
You REALLY need to speed up the shift timing, at least copy the performance shift timing tables into normal. The 4L80 and 4L60 need line pressure. If you haven't made any internal mods its ok, do not go over the 90psi max. Again copy the performance table into the normal for shift pressure, and it wouldn't hurt to increase about 10-15% after that too. Disable the TM traction control such as hold gear enabled unless you kept all the sensors and abs on that C10.

On your next log please scan for delivered engine torque. We don't have the torque output but the acceleration rate dropped off sharply while still in WOT right at 5700rpm. You should be shifting at that rpm and would be at your desired 61mph. Both flags must be met, WOT rpm and mph and setting the rpm lower can help stage a quicker shift as soon as mph is met. Again your normal table shows 39mph@81%TPS while 78% tps enables WOT. Inconsistent with the desired shift for 61mph at 6050rpm which is too high anyway.
In torque management for engine Max torque is set at 350lb-ft?
Check your trans fluid for burnt oil and right after the failed shift check for bubbles/ aeration on dipstick.
You have a turbo right and has the torque converter been upgraded? Watch the https://www.youtube.com/watch?v=QJatyWwKm4I really all of this series but this is on stator design.

Have fun.
07-02-2020
kingtal0n

Make sure you are using enough shift pressure

I would lower MPH very low so it just uses RPM for the shift

Then set the RPM very low and gradually increase it until it shifts when you want at the power level you are making

Power output will alter time it takes to shift because the more power you make the faster the engine is accelerating, whereas the shift is determined more by hydraulics.
In other words, if the ECU commands a 1-2 shift with 300hp at 5000rpm it will probably actually occur like 5100 or 5200
but when it commands a 1-2 shift with 500hp at 5000rpm the engine will accelerate farther in the time it takes to shift, so maybe 5400 or 5600rpm by the time it actually happens

this means when you set your shift points they need to be set lower and lower the more power you make, so you can't just keep increasing power or changing engine acceleration and expect the shifts to stay the same. Keep in mind the ECU uses TPS and not TORQUE to determine shift pressure. 640ft*lbs is 100% TPS whether you make 200 or 600ft*lbs
07-02-2020
smokeshow

1 Attachment(s)

Change this...

Attachment 101071

Your upshift vs downshift speeds are backwards. Those are supposed to allow dual calibrations to serve as a hysteresis, however yours are telling the transmission to command two gears at once. You can't shift into 2nd at 61mph but downshift to 1st at 71mph...not possible. Swap the upshift and the downshift values and you'll be on your way.
07-02-2020
Hondaeater

Quote:

Originally Posted by smokeshow

Change this...

Attachment 101071

Your upshift vs downshift speeds are backwards. Those are supposed to allow dual calibrations to serve as a hysteresis, however yours are telling the transmission to command two gears at once. You can't shift into 2nd at 61mph but downshift to 1st at 71mph...not possible. Swap the upshift and the downshift values and you'll be on your way.

Yep. The Shift speed vs TPS vs shift tables have downshift table at 100% TPS higher than upshift too.
07-05-2020
AndyGrove

Thanks all. I realize my error now. I must of copy/pasted the 100% TPS shift values and then added 10 mph instead of subtracting. I have updated my tune and will give it a try soon, but I believe this should solve my issues. I have made no changes to the tune in regards to pressure or shift timing. I installed a Jakes Stage 2 Kit, as well as there shift kit. I called them to ask what changes I needed to make to the software to support their kit, and was told just the shift scheduling and normal torque converter clutch changes. I have also read other posts, that if mechanically you have boosted pressure or installed shift kit, that making compensations in the software on pressure or shift timing was not needed. I have smooth shifts and cruise and hard shifts at WOT. So I was just curious, on your opinions if I needed to make any changes here, or leave well enough alone.

Thanks again for the help!
07-05-2020
kingtal0n

Quote:

Originally Posted by AndyGrove

I have also read other posts, that if mechanically you have boosted pressure or installed shift kit, that making compensations in the software on pressure or shift timing was not needed. I have smooth shifts and cruise and hard shifts at WOT. So I was just curious, on your opinions if I needed to make any changes here, or leave well enough alone.

I thought the same thing but I was wrong. I have an HD2 shift kit with the bigger boost valve etc...
The more power it makes the more pressure needed to command. The OEM shift table pressure was like 60PSI and after 380ft*lbs it started slipping 1st and toasted 1-2 clutch pack.

The only reason the OEM gets away with that low of pressure is they use torque management.

As soon as you remove TQmgmnt you need to add back a ton of pressure or it will slip.

The way to verify this is with a transmission pressure gauge. I am sure jakess told you to use a pressure gauge. Do NOT drive the car hard without one. You will NOT feel it slip.