Transmission tuning for economy

[Extinct]

Anyone try any trans tuning to improve fuel economy? My new daily commute has me on surface streets quite a bit now and I noticed that the truck shifts quite late compared to my gassers - probably 500-600 rpm later. Also, in looking at the stock tune it looks like they wait quite a long time to engage the TCC in the lower gears - any reason GM did that? I'm sure there is probably some mpg on the table there, just wondering if there is any possible harmful side effects if changes are made at really low loads (I am typically below 25% tp).

[Wheelz]

Only noticeable improvement I've seen is locking the TCC up in lower gears. I'm locking it up from 3rd and up. Just be sure to let it unlock if you go into high load or shift

[CwF]

Yes I have, but I think it's better to take the TCM as part of the powertrain that is as a unit tuned for the desired result. Tuning the Allison for my desire was a main purpose of EFILive as much as the Duramax.

Taken together, I set up a flow chart to develop my tune to avoid trying to tune factors to early highly dependent on others. Tuning the TCC in my opinion is one of those factors where others should be ironed out first. Always keep the desired torque curve matched and develop this FIRST. I can't imagine it shifting later than a gasser, even stock the tune is short shifting with a light switch throttle. You mention 25% TPS, that is the key to how it all works. I softened my curve pretty drastically to open up the range of adjustment in the tranny. So with a lazier build of power you have a few cells to allow adjustment instead of just one. My city cruise range is closer to 33%, highway over 50%. My cruise control became much tighter and smoother, even though logs hit 95%+ while there is more pedal left. I don't get that, TPS under cruise does not equal TPS under foot. Then , changing the torque ramp yields much better finesse, eliminate the light switch effect driving in traffic, and greatly reduces the slip range of the converter - ultimately eliminating the need for the TCC under light throttle and yields a much smoother drive. Misapplication of the TCC really just makes the truck more jerky unless the curve is more akin to a ZF6 tune.

Decide on a city path where you can hit common speeds, 25,35,45, etc and log it. Pick times when it can be made how you want it with little or no traffic. Log the tranny factors and watch the slip. Change the curves and see the effect. This takes a few times and note, the tranny will slowly adapt and temp will make a huge difference. It took me a few months to iron it out for my preference. I saw a factory slip of -200 to 500 rpm or so lightly throttling around those speeds and reduced it to 0-200. This is all throttle control and a match of the tunes, not just a tranny tune.

Next, my TCC will engage in 2nd, does hold through changes when throttled to do so. It also says disengaged in as high as 5th throttling a low rpm where the tcc would make that impossible while the slip is in a tight range. It can all be blended together to have action controlled by tps. The factory did not do that. The TCC will also stab every so often, ramp up to reduce slip by a few hundred rpm then disengage, often a split second after a upshift is engaged and the throttle steady.

Load is pretty irrelevent since you do have a TCM DSP2, right? The tow/haul switch. Make it a light throttle short shifter slash high throttle lockup master in normal mode and do whatever to the T/H settings for proper action with a load.

And I gave up on 2-3. I just can't get it perfect. Overall, my changes greatly improved city mileage and the overall drive. Other changes around 4-6th in the 45-75 mph range improved my mountain driving, much smoother, better gear holding, lack of that annoying tendency to downshift on tps lifting, and much better coasting. This gave a few mpg. And again, hit T/H and all that goes away.

[CwF]

D5196 compare:

[Dozerboy]

I played with shift points and didn't gain anything. The ECM is where all the improvements seem to be.

[THEFERMANATOR]

I played with shift points and didn't gain anything. The ECM is where all the improvements seem to be.

With a stock converter there isn't much to be gained as lowering the shift points simply makes the converter slip more since it is so loose to begin with. With my PI ML triple disk, I did see improvement by lowering my shift points down some as it couples at a lower RPM and lets me actually use it instead of just slipping the converter and making more heat.