Automatic transmission question

[Jrbrannan]

So I am loving my new JL and I think the new 8 speed is super smooth. I have driven it very easy as I am still in the break-in period.
I have noticed that when I am approaching a stop light and I lay off the gas and just let the Jeep cruise on it's own power the transmission downshifts smoothly but almost acts like an engine brake. Not huge but it seems like it slows even more than if I was cruising in neutral. Has anyone else noticed this?

I don't think there is a problem just wondering what other people's thoughts are.

Sponsored

 

[Fuel Fire Desire]

Thats the design of the new gen FCA 8 speeds. My challenger did it too, except in sport mode, where it was progressively more and more aggressive depending on brake pedal input force. It made a big difference in that instance. Being the JL does it in such a subtle manner, and I was so used to the aggressive downshifts of the challenger, I had forgot about it.

 

[Bubba33]

My rams do it too, the 8 speed is the best transmission I've ever had.

 

[Jrbrannan]

My rams do it too, the 8 speed is the best transmission I've ever had.

I guess it is good if you need to get back on the gas you be in the right gear but it seems a bit less fuel efficient... Okay I just said fuel efficient about a Jeep Wrangler... I should sit in the corner and not be able to comment for the rest of the day.

 

[Jeepsterfreak]

I guess it is good if you need to get back on the gas you be in the right gear but it seems a bit less fuel efficient... Okay I just said fuel efficient about a Jeep Wrangler... I should sit in the corner and not be able to comment for the rest of the day.

I’m certainly no engineer, but not sure it’s less fuel efficient. If it’s using engine braking by downshifting, the engine RPM is higher but that doesn’t mean it’s burning more fuel since your foot is off the gas. When you need to accelerate again, then you are already in a lower gear so you don’t need to press hard on the gas pedal to get going again if that makes sense.

Can you watch the displayed gear # drop on the cluster when slowing to a stop?

 

[Halfdoor]

My cluster doesn't show the gear. Just says D.

 

[BillyHW]

My cluster doesn't show the gear. Just says D.

There's a setting you can change somewhere that will make it show you the gear as a subscript to the "D".

 

[Sean L]

I guess it is good if you need to get back on the gas you be in the right gear but it seems a bit less fuel efficient... Okay I just said fuel efficient about a Jeep Wrangler... I should sit in the corner and not be able to comment for the rest of the day.

Deceleration fuel shut off is what happens in this situation. When your engine RPM is above Idle and your throttle is closed and the engine is at operating temperature your fuel injection will shut off. At that point all that's happening with your engine is air flow and no fuel burn. Its been that way with all fuel injection systems since at least the early 90s. If you bring up your fuel mileage screen you'll see the instant mileage jump up to 99 MPG when you're braking for a stop light/sign, that's when the fuel injectors shut off. This is also why coasting down a hill in neutral isn't as efficient as many people like to think.

 

[$uicide$hift]

Deceleration fuel shut off is what happens in this situation. When your engine RPM is above Idle and your throttle is closed and the engine is at operating temperature your fuel injection will shut off. At that point all that's happening with your engine is air flow and no fuel burn. Its been that way with all fuel injection systems since at least the early 90s. If you bring up your fuel mileage screen you'll see the instant mileage jump up to 99 MPG when you're braking for a stop light/sign, that's when the fuel injectors shut off. This is also why coasting down a hill in neutral isn't as efficient as many people like to think.

To add to this I believe this may be a way of using that energy to boost / charge the ESS battery which is why it would be set to a lower gear. Engine braking to turn that energy into power and charge the auxiliary battery.

 

[Jrbrannan]

That makes sense, thanks!

 

[Bubba33]

To add to this I believe this may be a way of using that energy to boost / charge the ESS battery which is why it would be set to a lower gear. Engine braking to turn that energy into power and charge the auxiliary battery.

I don't think so it has done it in my other 8 speeds. They don't have that start ,stop feature. The battery gets its charging from the alternator.

 

[$uicide$hift]

I don't think so it has done it in my other 8 speeds. They don't have that start ,stop feature. The battery gets its charging from the alternator.

Yes the regular battery you can see when you open the hood. I am talking about the smaller battery used for running the electronics and ESS located behind passenger fender.

 

[Bubba33]

Yes the regular battery you can see when you open the hood. I am talking about the smaller battery used for running the electronics and ESS located behind passenger fender.

Like I said I've had 2 other 8 speed and no start and stop. Now i have 3 with this new JL and they all feel the same.They work as a engine brake in a way. The benefit you can get from it is longer brake life.

 

[$uicide$hift]

The benefit you can get from it is longer brake life

Yes another benefit. I am not discounting that the transmission does this on vehicles without start / stop. I am saying I think that this is also using that energy to boost that secondary battery. I could be wrong as I know they stated the 2019 MY BSG would use that energy to charge that battery.

 

[sprk33]

I have the 18 JLUR and mine is doing the same thing....I just think it is the tranny downshifting....it is noticeable however, it is not jerky or anything.

Sponsored