Engine Braking

[Bluesman123]

This is not really a problem (I hope ) but I'm curious if anyone know what's going on.

 

When I'm slowing down from high speeds, like coming to a freeway exit, it feels like it is downshifting slightly. After putting a tach in it, however, I notice that the engine speed does not change enough to notice. Still, you can definitely feel something like a down shift and a deceleration (spelling -5 !).

 

Does anyone have this happen on your truck? Do you know what it is?

 

For the record, I'm running a stock 1997 5.7 Vortec and 4L60E tranny (taken from a 1998 Sierra ... I know...its a long story) in a 1991 Sonoma. Since I am in California, I have left everything stock so I can smog it and use it as a daily driver.

 

Thanks for your help,

 

Dave

[Cool Zr2]

SBC vortecs have economy mode or whatever its called, after a couple of seconds of coasting the torque converter locks up and uses the engine as a slight braking effect untill you use or tap the thorttle, then it leaves this mode. The motor runs really lean in this mode, its goes past the limits of my air/fuel ratio guage when it does it.

[Colorado Kid]

Yeah, REALLY lean, as in no fuel at all. What you're feeling is probably injection shut down. It's much more obvious in my '96 because I dont' have an automatic transmission.

[Cool Zr2]

Yeah, REALLY lean, as in no fuel at all. What you're feeling is probably injection shut down. It's much more obvious in my '96 because I dont' have an automatic transmission.

It dosen't matter if you have an auto or not the effect will be the same, once the TTC locks up it is direct drive like a manual.