4L80E : no engine brake

[Pinger]

Mine's a 7.4L, '80E, 3.73 axle.

You have pronounced engine braking in OD?

I don't know how. There's no mechanism for engine braking if the bands aren't applied--just lack-of-power and whatever friction / loss is inherent in the driveline and aerodynamics. Yes, the vehicle slows. No, that's not "engine braking".

OK, if there's no engine braking as the transmission is incapable of it in OD then the rpm will drop to idle on over-run. I'll check that tomorrow.

 

[Schurkey]

Mine doesn't drop to idle. It just drops lower than if the engine were holding steady speed.

As opposed to L1 or L2, where engine speed remains about the same as if the engine were holding steady speed (Maybe a bit lower due to torque-converter slip.)

 

[Pinger]

Mine doesn't drop to idle. It just drops lower than if the engine were holding steady speed.

Then the truck is driving the engine - engine braking - via the transmission.

The only difference between our two trucks is the engine and their fuelling strategies on over-run. I can configure mine and definitely there is engine braking.

Ford apparently eschewed over-run fuel cut-off (circa early 1990s - when the OHC modular V8 was launched) - GM the same?
I suppose I could try mine on gasoline and compare.

 

[Schurkey]

Then the truck is driving the engine - engine braking - via the transmission.

Consider the difference:

OD and D, the trans "drives the engine" so feebly that, while the engine doesn't go down to idle, the engine turns considerably slower than if the engine were maintaining an identical steady speed. The engine would have to speed up to hold whatever speed the vehicle is traveling at.

The vehicle slows down similarly to a manual-trans vehicle when you release the throttle and kick in the clutch pedal. In other words..."Coasting".

L2 and L1, the trans drives the engine so vigorously that the engine RPM is at--or nearly at--the same RPM as if the engine were maintaining an identical steady speed.

The vehicle slows down almost as fast as a manual-trans vehicle if you release the throttle but DON'T kick in the clutch.

The OP has stated that his engine DOES return to idle speed when off-the-throttle. Clearly, no engine-braking there.

 

[Pinger]

Consider the difference:

OD and D, the trans "drives the engine" so feebly that, while the engine doesn't go down to idle, the engine turns considerably slower than if the engine were maintaining an identical steady speed. The engine would have to speed up to hold whatever speed the vehicle is traveling at.

The vehicle slows down similarly to a manual-trans vehicle when you release the throttle and kick in the clutch pedal. In other words..."Coasting".
.

TC slip is another variable.
Your sentence in bold - without any slip the rpm would be linked to road speed. That it doesn't fall to idle means it is being driven by the truck's momentum - inevitably (unless fuelling strategy prevents it) a SI engine will provide engine braking in that circumstance. The vacuum pump that consumes no energy has yet to be invented.

Three variables that could influence engine braking on your truck and mine and lead to differing behaviour:
Fuelling strategy.
TC slip (re different stall speed)
FD ratio.

Last Thursday over 70 miles of hilly B-roads taken in OD I barely touched the brake pedal. When I got the truck I was struggling to hold it back on the brakes. The difference between the two is over-run fuel cut-off settings (that I can alter). My 4L80E will push the engine.

 

[Supercharged111]

TC slip is another variable.
Your sentence in bold - without any slip the rpm would be linked to road speed. That it doesn't fall to idle means it is being driven by the truck's momentum - inevitably (unless fuelling strategy prevents it) a SI engine will provide engine braking in that circumstance. The vacuum pump that consumes no energy has yet to be invented.

Three variables that could influence engine braking on your truck and mine and lead to differing behaviour:
Fuelling strategy.
TC slip (re different stall speed)
FD ratio.

Last Thursday over 70 miles of hilly B-roads taken in OD I barely touched the brake pedal. When I got the truck I was struggling to hold it back on the brakes. The difference between the two is over-run fuel cut-off settings (that I can alter). My 4L80E will push the engine.

350 had a looser converter than a 454 or 6.5, so could play into a lack of engine braking. I'm beginning to think this is the cause for the RPM drop, TCC unlocking and slipping and basically decoupling the engine from trans. I say this because my 1500 is tuned to stay locked when you lift like a 4L60 and I get good engine braking.

 

[PlayingWithTBI]

Do Vortecs have DFCO (Decel Fuel Cut Off)? I know when I had it enabled with my 700R4 going highway speeds in OD it still felt like I was hitting the brakes when I let up.

 

[Supercharged111]

Do Vortecs have DFCO (Decel Fuel Cut Off)? I know when I had it enabled with my 700R4 going highway speeds in OD it still felt like I was hitting the brakes when I let up.

They do have DFCO enabled. 4L60 keeps TCC locked when you lift, but the 4L80 unlocks with a lift.

 

[PlayingWithTBI]

4L60 keeps TCC locked when you lift, but the 4L80 unlocks with a lift.

Ahhh, gotcha

 

[Pinger]

If I remember, I'll check the DFCO later today when I'm out.
I can swich between LPG (where's there's engine braking) and gasoline. On gasoline I can also disable the pump with a switch on the dash.