Help w/ strange TC/Shift issue with Fuel Sipper tune

[cleatus12r]

DJ,

I went out and drove it today. First off.....wow. I'm glad that everyone is entitled to their opinion. It's not a bad program, but it's definitely not for me.


Anyway, I was able to duplicate what I think you are feeling....it did it once for me.

Without knowing exactly what to expect and when to expect it, my first instinct is that as the 4-3 downshift is occuring, the torque converter is unlocking. That's normal. The bump you feel after that is the TC locking back up for 3rd gear since you're still at a road speed that allows TC lockup in 3rd.....but just barely. I think it happened at 37 MPH (indicated) up a small incline, low load, and slowly losing speed. It did "double bump" so to speak.

What needs to happen here? Either the 4-3 shift needs to occur earlier (higher speed), later (lower speed), the TC apply rate needs to be slowed down to take away from the "jerk" feel, or the TC relock time after the 4-3 downshift needs to be eliminated.

Raising the 4-3 downshift speed would allow the transmission to downshift before the engine gets to 1200 RPM and help by not transferring as much torque during the downshift. Lowering the downshift speed would allow a 4-3 downshift without an attempt to relock the torque converter in 3rd.

I would do a combination of a few things. I would change the relock time after 4-3 downshift to something rediculously low like .13 seconds. This will get rid of the perceived "flare" and then jerk on relock. I would also raise the 4-3 downshift speed by a couple MPH.....it's not really doing you any favors having it unlock at 37 MPH. You're also right about the harsh TCC apply. Since it's a file meant for economy, it's not meant to be "hogged on" and therefore very low APP is usually used. I'd lower the TCC apply duty cycle a bit in the lower load ranges too.