95 4l80e drops to idle in 4th.

[WarWagon]

:skep: Ok this is weird. If I take my foot off the throttle at 2500 RPM it will drop to 700 RPM, idle, while running down the freeway in OD, 4th. I don't recall it doing this before.

 

[handcannon]

You've got me curious now. It seems like my K2500 4L80E also drops to idle, although I haven't really paid any attention when up to highway speed. I do know when at slower speeds it will drop to idle when I take my foot off the throttle. The torque converter will unlock and the RPMs will drop to idle. I'm thinking it will do the same thing when the RPMs are higher. The only time I know of for sure that the RPMs stay up when taking my foot off the throttle is if I have the torque converter manually locked.

Don

 

[NVW]

Sounds normal, step on the brake and it drops to about 600 rpm IIRC.

 

[ak diesel driver]

Sounds normal, step on the brake and it drops to about 600 rpm IIRC.

x2

 

[tanman_2006]

Mine doesnt drop all the way to idle, more like 1100

 

[WarWagon]

Sounds normal, step on the brake and it drops to about 600 rpm IIRC.

Ok it is a TCC lock thing in the tune then.

 

[tanman_2006]

Ok it is a TCC lock thing in the tune then.

That's what i would guess. We both have buddy tunes and my results are in econ.

From 65 it drops to 1100 then quickly falls with decel.

Sent from: Source Unknown

 

[dka99burb]

i wish mine did this better. My torque converter seems to backdrive the engine some. Now, my Grandfather's 04 Buick Lesabre coasts forever! Lift the pedal and it's in neutral = great highway mileage. Is there a way we could set the 4L80E to do something similar and place a switch to turn it off when towing?? I bet we could gain a few mpgs for folks DD their trucks, specially on the hwy.

 

[WarWagon]

Well it is weird in some traffic situations when the engine RPM is all over the place as you are needing light to no throttle. The compression braking when you get off the throttle is sometimes useful so you don't have to hit the brakes. Personally I hate the coast forever that sedans do.

I had trouble with the TCC staying locked on lift causing a surge downhill so I had it turned off.

To improve mileage you lock the TCC at a lower MPH. For some reason GM refused to do this below 45 MPH on a lot of things. We were seeing MPG improvements on Trailblazer SS's locking at 35 MPH and releasing on more than light throttle.

 

[dka99burb]

I was only referring to doing it at highway speeds. Otherwise, I would agree with you completely. It is annoying.
But, at highway speeds it is very efficient to coast down all downhills without engine breaking.
I would definitely want a way to turn it on and off.
My wifes 3.5 Altima engine brakes a lot while the Buick Lesabre does none at all. Altima is easier to drive in town, Buick better on hwy. I wish I could have both on one vehicle with the flip of a switch.

Apparently, I do not have the option to add a switch for TCC lockup on my 99 since it is OBDII?

BTW, early in my ownership of the Burb I had issues with the TCC bouncing in and out while on downhill and sometimes cruising under very low load. Turned out that the IP was worn out. I replaced it and that solved that issue. It was throwing too much fuel at very light calculated loads. Barely touch pedal and it would accel quickly. Threw the CC for a loop too. I don't know if that is realitive at all, but it is typed now.. LOL