Deceleration issue on 05 Envoy Ext V8 3.73

[ronbrau]

Bought the car approx 2 months ago. I am aware now of a variable time delay (depending on speed, gear) between taking foot off gas pedal and how soon the vehicle starts to decelerate. Also, when decelerating from speed > 30 mph, in drv, 3rd or 2nd, when the speed approaches approx 25mph, the computer maintains engine rpm such that veh speed remains relatively constant at 25mph. After approx 30 sec or more, the veh will gradually decel until approx the normal idle rpm is reached. In 1st gear the time delay is much shorter ( a sec or two) but still noticeable. I talked to two local dealer service reps who have'nt a clue. I intend to drive some envoys on used car lots.

[RayVoy]

Your not alone, mine has the same annoying problem. I think they all do it. I complained to the dealer, he came me the keys to a new one, same thing. It's able to do it because of the "drive by wire" throttle and the computer com trolling the throttle position. My dealer told me it was for economy, but that does not compute for me.

[rbarrios]

if I understood correctly- I can see why its for fuel mileage....
most people have a bad tendency to drive in such a way where they step on gas- let go (car slows down) then they jab the gas again, speed up, let go, and slows down- they continously do this- and in deed- doing this wastes ALOT of gas because youre constantly accelerating to get back up to speed.
By keeping the RPMs up there- the vehicle does not slow down as much and its not going to waste as much gas when you step on the pedal to get back up to speed...
When I drive- and I see a red light up ahead- I just let off the gas- let the vehicle coast- and coast it does- then it reaches a point where it starts to slow down a bit faster- usually I get to the intersection as its turning green, and I gently accelerate...
works for me...........
I get 300 miles on 16 .7 gallons.....
Hopefully I read the post correctly ( I have the I6)

[Envoy Fan]

Maybe a DOD problem?:undecided

[RayVoy]

if I understood correctly- I can see why its for fuel mileage....
most people have a bad tendency to drive in such a way where they step on gas- let go (car slows down) then they jab the gas again, speed up, let go, and slows down- they continously do this- and in deed- doing this wastes ALOT of gas because youre constantly accelerating to get back up to speed.
By keeping the RPMs up there- the vehicle does not slow down as much and its not going to waste as much gas when you step on the pedal to get back up to speed...
When I drive- and I see a red light up ahead- I just let off the gas- let the vehicle coast- and coast it does- then it reaches a point where it starts to slow down a bit faster- usually I get to the intersection as its turning green, and I gently accelerate...
works for me...........
I get 300 miles on 16 .7 gallons.....
Hopefully I read the post correctly ( I have the I6)Yep, I can c where ur comming from, it does take a while to get used to it, felt like I was going to run up someones pipe at first.

Maybe a DOD problem?:undecidedNo, mines a I6, looks like it's on both

[ScarabEpic22]

Its not a DOD problem, but its how GM setup the DFCO tables in the PCM/ECM. I changed my DFCO settings to some that dfe1 on the EFILive forum is running in his EXT, which really changed the decel feeling a lot (there is engine braking now). I cant say if it improved mpg or not, but Im still testing it to see what happens.

Basically what he/I did was expand the operating parameters for DFCO so it stays active from 29mph+ on accel and shuts off when 22 mph is hit on decel.

[ronbrau]

Thanks for the info ScarabEpic22. I suspected all along that software was the heart of the issue. I will study it a bit, being a retired EE, but am a bit leery of mods to the oem code. What seems strange to me is why, on a veh that has some pretensions to handling offrd situations, the manuf would prevent engine breaking in 2nd gear - even in low range!! A driver manually downshifts to a lower gear for a reason. The DFCO mph set points should have been influenced by transmission operation.

[RayVoy]

Its not a DOD problem, but its how GM setup the DFCO tables in the PCM/ECM. I changed my DFCO settings to some that dfe1 on the EFILive forum is running in his EXT, which really changed the decel feeling a lot (there is engine braking now). I cant say if it improved mpg or not, but Im still testing it to see what happens.

Basically what he/I did was expand the operating parameters for DFCO so it stays active from 29mph+ on accel and shuts off when 22 mph is hit on decel. Thanks Erik, This problem was the reason I was roaming around on the web and found this site. Always something good from every problem.