4L80E operational questions.

[Stalker L-67]

First post in ~15 years!

Stock 6.0/4L80E in a 2002 Blazer and a daily driver. Looking for MPG and I have read most of the posts referencing this.
Im asking questions to learn and identify changes worth looking into.


My questions are:

1. The torque converter must unlock to up/down shift, yes? I am 99.9% sure the answer is yes.........

2. On my vehicle the torque converter only locks up in 4th and over ~50 mph. From what I have read, changing the point it locks/unlocks is pretty straight forward. How low of a MPH can you safely lock the converter?

3. Can I make the converter lock up in gears other than 4th. Is this a good/bad idea?

4. When doing the engine swap I used a harness that does not have the "tow" button. What are the ramifications of not having the tow button? Years ago my Silverado seemed to tow fine using/not using the tow button. Adding a tow button is pretty easy, but do I need to?

5. When coasting the converter unlocks when I take my foot off the gas. Is it better to unlock or keep it locked? What are the benefits of unlocking vs keeping it locked when coasting?

6. At hiway speeds coasting down a hill the vehicle slowly starts picking up speed after a ~7 mph speed increase I feel braking taking place and the vehicle is slowing down now. At the same time I noticed the torque converter slip is now -200 rpm where as before it was a positive number. Is this the DFCO kicking in?

Just getting information to discuss with my tuner who uses HP Tuners. I am thinking of purchasing again, but am not sure if I will use it enough once the vehicle is dialed in.

Thats it for now.
Thanks in advance.

[RDF1]

First post in ~15 years!

Stock 6.0/4L80E in a 2002 Blazer and a daily driver. Looking for MPG and I have read most of the posts referencing this.
Im asking questions to learn and identify changes worth looking into.


My questions are:

1. The torque converter must unlock to up/down shift, yes? I am 99.9% sure the answer is yes.........

2. On my vehicle the torque converter only locks up in 4th and over ~50 mph. From what I have read, changing the point it locks/unlocks is pretty straight forward. How low of a MPH can you safely lock the converter?

3. Can I make the converter lock up in gears other than 4th. Is this a good/bad idea?

4. When doing the engine swap I used a harness that does not have the "tow" button. What are the ramifications of not having the tow button? Years ago my Silverado seemed to tow fine using/not using the tow button. Adding a tow button is pretty easy, but do I need to?

5. When coasting the converter unlocks when I take my foot off the gas. Is it better to unlock or keep it locked? What are the benefits of unlocking vs keeping it locked when coasting?

6. At hiway speeds coasting down a hill the vehicle slowly starts picking up speed after a ~7 mph speed increase I feel braking taking place and the vehicle is slowing down now. At the same time I noticed the torque converter slip is now -200 rpm where as before it was a positive number. Is this the DFCO kicking in?

Just getting information to discuss with my tuner who uses HP Tuners. I am thinking of purchasing again, but am not sure if I will use it enough once the vehicle is dialed in.

Thats it for now.
Thanks in advance.

1. The torque converter must unlock to up/down shift, yes? I am 99.9% sure the answer is yes.........
It doesnt "have" to unlock but if its locked then the shift is very harsh since there is no "cushion" in from the converter during the shift. I have my 4l80 locked during shifts but had to use 100% TM to get it to soften up where its not noticeable.

2. On my vehicle the torque converter only locks up in 4th and over ~50 mph. From what I have read, changing the point it locks/unlocks is pretty straight forward. How low of a MPH can you safely lock the converter? Depends on your gear/tire combo.

3. Can I make the converter lock up in gears other than 4th. Is this a good/bad idea?
I have mine locking in 2nd, 3rd, and 4th for tow/haul. Keeps the trans temps down towing heavy stuff on back roads. Its a personal preference.

4. When doing the engine swap I used a harness that does not have the "tow" button. What are the ramifications of not having the tow button? Years ago my Silverado seemed to tow fine using/not using the tow button. Adding a tow button is pretty easy, but do I need to?

Not having tow button means no way to use the tow/haul shift settings. The easiest way to add it is a momentary button going to the PCM. ECM455 is the way to change how tow haul is engaged. But for some reason HP doesnt give you any more info.

5. When coasting the converter unlocks when I take my foot off the gas. Is it better to unlock or keep it locked? What are the benefits of unlocking vs keeping it locked when coasting?
You can change the settings to keep it locked, but only in 4th gear unless you move the shifter to the gear you want it to stay locked in because the over run clutches aren't engaged unless your in that gear manually. I like to keep it locked so when i get back on the throttle its still locked.

6. At hiway speeds coasting down a hill the vehicle slowly starts picking up speed after a ~7 mph speed increase I feel braking taking place and the vehicle is slowing down now. At the same time I noticed the torque converter slip is now -200 rpm where as before it was a positive number. Is this the DFCO kicking in?
Yes it could be DFCO as well as TCC unlocking. Get a datalog of it happening and post it here.

Post your tune as well.