Does your Envoy "Decelerate"? (auto trans)

[Sqrly]

Once I get moving in drive, at any speed, if I take my foot off the accelerator pedal, the engine rpm drops to about 1,000 and the vehicle just coasts.

There's no engine braking in drive. If I manually downshift, the rpms jump up and I feel deceleration.

Is this normal for a 04 Envoy 4WD XUV?

 

[TJBaker57]

My 2002 TrailBlazer will keep the torque converter locked until I drop below a certain speed. I think it's 40 mph. As long as I do not touch the brake it stays locked and the engine drags down the vehicle speed.

On a related note on longer downhills my 4.2 LL8 fuel injectors completely shut off. My 2005 5.3 Yukon doesn't do this.

Not sure if either is normal for the respective vehicles.

 

[Mooseman]

Sounds normal to me.

 

[59840Surfer]

In MANUAL 3rd/Direct gear, there WILL BE engine braking --- because, contrary to peoples' thoughts, using the lower gears ranges) is designed for engine braking, not accelerating.

IOW --- we don't manually upshift (unless we're still goofy kids) but we do downshift.

ANY manual gear placement besides OD/4th will produce engine braking - this is designed for those times when you have some long downhill runs and are carrying a couple of very obese people or a 10,000 lb trailer and you want to save the brakes for when you actually need them.

FUN FACT: SOME transmissions (by factory calibration and certainly not all) will start in 2nd/Intermediate when you put the quadrant selector in that position --- this is to lower the torque to the rear wheel (all wheels in 4WD) and raise the torque convertor to its stall value without TCC/LU so you can start up from a stop with little to little-to-no wheel spin.

This will force the (what else can you call it) TORQUE CONVERTOR will be in full torque reduction. Hence the name TORQUE CONVERTOR is a truism(*) --- that's what it does ... convert torque! Amazing.

(*) like: SHOCK ABSORBER --- the name says it all!

I digress ...............

YES --- if the factory calibration allows it --- the fuel will shut off in a manual gear setting IF the plenum vacuum gets to a preconceived metric.

The oxygen sensor heaters will come on, anticipating a flow of fuel in a while, but trying to keep themselves ready as necessary --- according to the ECM programmer at GM in this case.

If, in 4th/OD when you take your foot off the accelerator --- the oxygen sensors will still be getting sufficient readings to keep the cat(s) happy because there will still be fuel a-flowing(*), and there'll be no need to turn the heaters ON --- but there will be NO engine braking.

(*) not much fuel because there's not much air either with the throttle plate closed --- this will theoretically be the same as IDLE-MODE and the AFR will still be 14:1.

I hope this clarifies(*) some concepts.

(*) For Teenagers: lissen at me hard here --- ya heya?

 

[gmcman]

If I remember correctly, I believe it's tuned that way to close the TB slowly to avoid a jerking from a sudden deceleration. If you notice, once you let off the gas, it keeps coasting without slowing then a couple seconds later it begins to slow under engine braking.

 

[Sqrly]

Mine never applies engine decel at any speed while in drive. It is not always the same RPM though. I tried coasting at 70mph, the rpm drops to just below 1800, the stall speed of the convertor.

I may be more sensitive to it as our 2017 Honda Accord with a CVT has decel programmed in. At 25mph or lower it is so strong it feels like the brakes are being applied.

 

[59840Surfer]

Mine never applies engine decel at any speed while in drive. It is not always the same RPM though. I tried coasting at 70mph, the rpm drops to just below 1800, the stall speed of the convertor.

I may be more sensitive to it as our 2017 Honda Accord with a CVT has decel programmed in. At 25mph or lower it is so strong it feels like the brakes are being applied.

Your observation is correct.

I cannot and will not speak of the Honda.

About "stall speed" however, it doesn't work in retard, but only during power-on.

What you say is not necessarily incorrect, just a fluke of your evaluating a factor from the backside of its design.

Good catch, though!

 

[Sqrly]

Your observation is correct.

I cannot and will not speak of the Honda.

About "stall speed" however, it doesn't work in retard, but only during power-on.

What you say is not necessarily incorrect, just a fluke of your evaluating a factor from the backside of its design.

Good catch, though!

Yeah, it's the ECM that's controlling the RPM. I just thought it was worth mentioning since it's just below the stall speed.

The Honda CVT's are awsome, now. They've evolved a lot even though their past is all people seem to talk about. Accords are not small cars and ours gets 40 mpg.