05 LLY Duramax defueling troubles

I noticed another individual posted about the same issue last year and never got back with nick. Hoping to gain some understanding. I’ve heard that LLY’s can be notorious for issues with defueling. I wrote a tune very similar to nicks in the course, but this truck isn’t too happy with it. Shifts aren’t clunky, but the truck will defuel from (for example) 16,000psi to 8,000psi before it will apply the next gear. I’ve read that I need to adjust the base torque and torque limited injection quantity tables. If possible, i’d like to gain some understanding on modifying these tables before I attempt to change them.

Thanks in advance!

Joe

Hey Joe,

The defuel control for the Allison is a bit dicey on the earlier trucks. The tables you referenced do impact the defuel, but they're more of a 'feed forward' type lookup table. In my experience they seem to control the initial defuel rate as the truck enters/exits the shift but they do not control the defuel or torque reduction rate during the shift. My suspicion is that there are some missing tables related to the dynamic defuel rates based on shift progress. For example, if the shift appears to be taking longer than the TCM expects you'll see an abnormally long defuel commanded by the TCM. If the shift is happening quickly then the defuel will be quite short.

In my experience, you can do one of two things.

A. Turn off the defuel in the TCM (D5197/D5196) and force the Allison to learn to shift without it.

B. Pay close attention to the way the factory throttle slopes in. Take care not to add too much power to early in the pedal so that you don't push the Allison way out of it's comfort zone. Remember, if you double the torque on a given shift from 200 ft/lbs to 400 ft/lbs you can expect the Allison to have a hard time dealing with it. This is an especially easy mistake to make by loading up the fuel early in the pedal travel.

Does this make sense?

Nick

Hey Nick,

Thanks for the response man. I’m following what you’re saying. I didn’t adjust anything under what would be about 50% throttle, but maybe if I was a little more conservative the truck would be happier. ..Wouldn’t it be certain to cause more wear by turning off the defuel in the TCM? ..would transmission tuning be the next piece of the puzzle in solving this issue?

Joe,

The way in which power is ramped in 'over stock' has everything to do with shift quality and ultimately the drive-ability rating of the tune. Continue to experiment with where and how aggressive you ramp in power and you'll see what I mean.

Yes, disabling defuel is harder on trans components. With that said, your typical built Allison (our DT 550 or DT750 for instance) is usually content to put up with no-defuel shifts for the life of the trans at the rated power level.

Nick

Thanks Nick! Really appreciate the good word, got a new tune to flash tonight that i wrote with your advice in mind. ..thanks again for the knowledge, it made a lot of sense when rewriting this calibration. hope it works out! i’ll report back this week

..and I’ll have to tell my brother to buy one of your guys’ builds for his allison. Then we’ll be able to really start talking power. ..It’s his truck, and he’s not willing to let me turn off the defuel until he builds out that trans haha can’t blame him

take care nick