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.