4L80E/4L85E 8.1 TCC Minimum Speed and Factory Lockup-Shift Tuning

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January 25th, 2022
nonnieselman

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Attachment 24025

Just for the heck of it, give this a try and see if the TCC acts different.

I searched all my tunes and i don't see that OS. I know on the larger trucks with the 8.1L there are several tables that we cant get to.
On a friends Kodiak with a 8.1L the Throttle wouldn't go over 50% over a certain speed. Ended up finding the original guy that did the calibrations on those trucks for GM and sure enough after changing some stuff to the 2500HD Truck tunes it made all the difference.
January 25th, 2022
joecar

Quote:

Originally Posted by gearheadE30

I've tried to reply and it says the post has to be approved by a moderator. Is it just going into some black hole in the internet?

EDIT: any time I write more than a sentence, I get the moderator approval message. This is frustrating.

For some reason it happens automatically, I'm not sure why it happens.
January 25th, 2022
joecar

Quote:

Originally Posted by gearheadE30

So all of your points are what prompted me to post here in the first place.
a. I would tell me I am crazy too, if I didn't see it for myself. With the stock, untouched tune straight from GM, a WOT acceleration shifts from first to second, locks the converter around 3500 rpm in second, and then eventually shifts into 3rd with the converter still locked. I have the datalogs to prove it on the other computer, can share if interested. But no joke, that is how GM set it up. I even verified on youtube with all those silly 0-60 videos people post: every 8.1 suburban out there you can see locking the converter in second at WOT.

b. stock tables will kick down before unlocking the converter in both 3rd and 4th when given heavy throttle. You're right, if it didn't kick down it would probably slip, but the stock tune is pretty aggressive about staying locked. I'm not interested in making it any more aggressive at high load than GM did.

c. Stock tune drives lockup in 2nd at 45 mph over 93% throttle, and 3rd at 55 mph over around 50% throttle so towing often gets you to part of the map where it locks up in 3rd before you hit the 3-4 shift point.

TCC slip is in all my logs now but I haven't done a WOT test since I added it. I'll have to see what it is doing during those shifts.

Very true - not wanting to go that low on this truck. The main motivation is I can watch instant economy (and injector pw) go from 13 mpg to 16-17 mpg as soon as the converter locks between 45 and 50 mph. Most of my around-town driving is 40-45 mph, so holding lockup down to 1400-1500 rpm instead of 1600-1700 would make for a meaningful improvement.

I've since tried a few more cals, with limited luck. Still trying to answer this question: is there some reason why I can't get the torque converter to lock below 45 mph? This seems to be the minimum regardless of gear, i.e. if I have the shifter in 3rd and the converter table is set to lock 3rd at 30 mph, it still doesn't lock until 45.

In an effort to get rid of GM's 3-4 shift with the torque converter locked, I'm trying to move the 4th TCC apply speeds up higher. But either that isn't working, or there is an error of 15+ mph between when the TCC apply is commanded and when it actually occurs. I'll keep moving it out until I see it make a difference, but haven't found that point yet.

Various of GM's tunes are not done sanely, they have other objectives in mind (or maybe they gave it to the interns).
January 25th, 2022
gearheadE30

@joecar - no worries, I'll just be brief in my messages or multi post longer stuff. Now that I know it will let me do short posts at least I can work around it now.

@nonnieselman - I think you'd get a giggle out of my current tune - I ended up at very similar changes to the shift patterns that you have. 3-4 upshift in particular, the lines are almost on top of each other.

Is there something different in the engine OS section? It's telling me the checksum changed, but not giving me a visible parameter for it. I'm in the habit of checking tunes having bricked an ECM with someone else's tune on a different car in the past - nothing personal just being cautious before I go test it :thumb_yello:
January 25th, 2022
gearheadE30

@joecar - no worries, I'll just be brief in my messages or multi post longer stuff. Now that I know it will let me do short posts at least I can work around it now.
January 25th, 2022
gearheadE30

Quote:

Originally Posted by joecar

For some reason it happens automatically, I'm not sure why it happens.

Strange. Okay, I'll deal with it then.
January 25th, 2022
gearheadE30

Quote:

Originally Posted by nonnieselman

Attachment 24025

Just for the heck of it, give this a try and see if the TCC acts different.

I searched all my tunes and i don't see that OS. I know on the larger trucks with the 8.1L there are several tables that we cant get to.
On a friends Kodiak with a 8.1L the Throttle wouldn't go over 50% over a certain speed. Ended up finding the original guy that did the calibrations on those trucks for GM and sure enough after changing some stuff to the 2500HD Truck tunes it made all the difference.

I think you'd get a giggle out of my current tune - I ended up at very similar changes to the shift patterns that you have. 3-4 upshift in particular, the lines are almost on top of each other. I also didn't find anything else with this OS, but there is so little information about the 8.1 around. That's pretty interesting about the Kodiak - if I had a .bin I'm sure I could go crazy trying to find stuff in there, but I'm not sure I care enough to expend that kind of energy.

Is there something different in the engine OS section? It's telling me the checksum changed, but not giving me a visible parameter for it. I'm in the habit of checking tunes having bricked an ECM with someone else's tune on a different car in the past - nothing personal just being cautious before I go test it :thumb_yello:
January 26th, 2022
nonnieselman

I understand completely.
I only changed shift points and TCC settings. nothing in the engine side of the tune.
Ill look for the Kodiak tune in a little while.

To play it safe just do a compare and copy the TCC and Shift parameters over. Id be interested if anything helped or if there is anything in the background that is limiting you..
Similar to the 4l80e Minimum TPS TCC unlock on the LS1B pcms. You have to make a CAX file or use HP Tuners to change it.
January 26th, 2022
gearheadE30

Quote:

Originally Posted by nonnieselman

I understand completely.
I only changed shift points and TCC settings. nothing in the engine side of the tune.
Ill look for the Kodiak tune in a little while.

To play it safe just do a compare and copy the TCC and Shift parameters over. Id be interested if anything helped or if there is anything in the background that is limiting you..
Similar to the 4l80e Minimum TPS TCC unlock on the LS1B pcms. You have to make a CAX file or use HP Tuners to change it.

the minimum TPS thing definitely is definitely true here too, even with those TCC tables. I'm not sure the .CAX that Lextech was using would work or not, and even if it did he doesn't seem to be too active these days. I've not found a copy of that file to try out, but it sure would be nice to be able to stay locked at 0% throttle. I don't care enough to go out and get HPT just for that though.

There is also some other processing going on for it to decide if it wants to lock. Sometimes it will go in at 45 mph. Sometimes it will wait forever at 55 mph and then lock. Not getting any misfires or anything, it just seems like it is waiting for some other condition to be met.

I did get a chance to try it out, but only briefly. Biggest difference is the VSS and speedo are way off compared to GPS. The stock settings are dead nuts on VSS and 2 mph off at 55 for speedo. However, if I ignore the speedo and just look at GPS, yes it does make the converter lock up at a lower speed in 4th. No lockup in the other gears, so it is responding to changes. So I suppose one option would be to skew the VSS high and then change the speedo output signal to make that accurate again if I really want to pull lockup speed down. Not sure what side effects that would have.
January 26th, 2022
nonnieselman

Ok good atleast that answers one question.

So there is a difference in the Speedometer versus what the PCM calculates in the background.. I found out the hard way. Just cause the speedo shows "45mph" it might be calculating "42mph" in the background..
I caught a ton of issues with a truck last year that had a 4l80e / 38s /"4.10" gears ( he told me it had 4.56 but it didnt) it took me quite awhile to figure out what was going on. Once i got the tune fudged enough everything started working but the speedometer needed adjusting to match the VSS in the scan tool.

Lex is around. I email him every now and again and he gets back to me pretty quick to be a busy working man.
Never hurts to ask him. Do you have his email?

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