Slow to command shift, hitting fuel cut 4L80E

[HRD]

I've been struggling with this one. I've got a turbo'd 5.3 with a CK Performance built 4L80E, Circle D tripple disc billet converter.
The problem is the PCM is slow to command a gear change and the engine is banging the limiter before it shifts. It's generally blowing the tires off when this happens, but I still think it should shift a little quicker. I've been logging current gear and it seems to sometimes take almost a second for it to shift. I've tried reducing the shift speed and RPM (It's currently set at 5500 RPM) and also reducing the shift time but it still does it. I've got the limiter set to 6200 RPM. Check out frames 2267 to 2282 in the attached log. You can see it takes it almost a second to donwnshift to 2nd when I go WOT then it doesn't upshift till I lift. Maybe I'm missing something here. Again at frame 2419, it finally shifts 1-2 but only after its hit the limiter a couple times.
The tune is a 3 bar SD scaled 50%
I appreciate any suggestions and help. Feel free to critique the tune as it is a work in progress and I am still learning.

t32.hpt t32.hpl Gen III 3bar.cfg

[HRD]

No one??

[Russ K]

Ok, first you need to get your calculated tire size to match the current tire size. Then your trans revolutions/mile will be correct, as that is what the PCM uses to determine the shift MPH.

So the formula is; calculated tire/current tire*trans revs/mile. Then close & open the speedo tab, and now your calculated tire will match the current tire size.

Russ Kemp

[HRD]

Thanks Russ. I'll give that a shot. I thought that as long as the MPH reading was right in the scanner then all was good. So now my understanding is the trans speed calculations are independent of the MPH read by the scanner and they may not actually match. Correct?

[HRD]

For future reference, Russ's formula "calculated tire/current tire*trans revs/mile" gives the new trans rev/mile to get the correct calculated tire value.

[HRD]

Well thanks to Russ's help and use of the Bluecat transmission software, it is shifting much better. It will now actually shift under WOT, but occasionally does still hit fuel cut one time right as it's about to shift. It seems like the WOT shifting is not real consistent, often overshooting the shift point by 700 rpm. I've seen a few tunes where the Full Throttle upshift speed has been zeroed out, I'm guessing so that it is only dependent on RPM for WOT shift points. Good idea??
Here's the latest tune and log. See frame 897.

Gen III 3bar A.cfgt33.hplt33.hpt

[Russ K]

Look at your WOT 2-3 shift speed tables, their at 72 mph. Your hitting the rev limiter before that. The WOT shift speeds in the editor need to be ~10% lower than your desired WOT shift speed. The upshift speed has to be met BEFORE the upshift RPM.

Russ Kemp

[HRD]

Man, how did I miss that? Thanks again.

[HRD]

OK, I've dialed the boost back some to get a better picture of what the trans is doing or what is being commanded. The advice that Russ has provided has been extremely helpful in getting the shifts nailed down. However, I'm still having problems with delayed 1-2 shift, especially following a downshift. Is there possibly a minimum time before upshift from 1st following a downshift? Please take a look at log t37, frame 184. In the tune, the shift speed for 1-2 is set to zero mph and 5800 rpm, yet its still hits the 6300 rpm limit before the PCM commands a shift. Now the 2-3 shift on the other hand is almost spot on. It seems like if I nail it before it gets into second so that there is no downshift, the 1-2 shift is much quicker and most often doesn't hit the limiter even though the RPM is climbing very fast. Now the other issue which seems to be intermittent is a delayed downshift from high gear. Look at log t37 frame 433. There is a full second that passes from when it goes WOT till it downshifts out of 4th. Whats causing that?

Now please look at log t37a, frame 598. Again, following a downshift to 1st, it bangs the limiter hard before finally deciding "oh, maybe I should command a shift now that I'm 500 rpm past my shift point."!! Now check out t37a frame 723. It takes over a second for it to command a downshift from 4th at WOT.

Thanks for checking this out and helping me with getting it dialed in.

Joe

t37a.hpl
t37.hpl
t37.hpt
Gen III 3bar.cfg

[HRD]

Bump

[rhackstall]

Im having this same issue, was this ever resolved?

[HRD]

I switched to Holley EFI and was much happier.

[rhackstall]

I switched to Holley EFI and was much happier.

so the controller was the issue? not the trans

[HRD]

Yes. Seemed to be the case

[RDF1]

I switched to Holley EFI and was much happier.

Haha holley makes things so much easier!

[rhackstall]

thanks