Having tested this out for over a week now, theres some big limitation to the fuel cut-off while coasting.
First, it is definitely speed sensative, I was stuck in traffic this morning and rolled downhill for well over a KM at about 30 to 40 KPH. The engine was running the entire time. The fuel cut off never came on. On many hills, the cut-off works just like an engine break and you have to either feather the pedal to keep a constant speed, or let the speed fall and speed up again.
And on short trips it almost never cuts off because the engine isn't up to temperature yet.
What's more fuel efficient: coasting downhill at 100 KPH at 1800 RPM feathering the pedal to keep a consistent speed, or shifting to neutral and idling at 500 RPM.
Without having a computer hooked up, I think there is still something to be had by shifting into neutral (real or unreal safety concerns aside).
And just to correct a statement about outsmarting the computer... The computers in these things are tasked to do some very specific things. And one of those tasks isn't "achieve the best fuel mileage possible". It is a balance between achieving operating temperature, maximizing power, drivability, comfort, etc.
As a example, one of the truck show that runs the "Ike Gaintlet" was quite frustrated with the new GMC 2500 or 3500 because I'm tow haul mode, the transmission was not smart enough to keep the engine in the peak power range. As a result, the truck would hit the desired speed and wid slow down as the RPMs fell. It would finally shift to a lower gear and accelerate back up to the desired speed. This cycle continued all the way up the hill. Ms the speed drop off was 10 to 15 MPH. A person could easily fix this by shifting the tranny to the appropriate gear and hold the same speed all the way up the hill.
First, it is definitely speed sensative, I was stuck in traffic this morning and rolled downhill for well over a KM at about 30 to 40 KPH. The engine was running the entire time. The fuel cut off never came on. On many hills, the cut-off works just like an engine break and you have to either feather the pedal to keep a constant speed, or let the speed fall and speed up again.
And on short trips it almost never cuts off because the engine isn't up to temperature yet.
What's more fuel efficient: coasting downhill at 100 KPH at 1800 RPM feathering the pedal to keep a consistent speed, or shifting to neutral and idling at 500 RPM.
Without having a computer hooked up, I think there is still something to be had by shifting into neutral (real or unreal safety concerns aside).
And just to correct a statement about outsmarting the computer... The computers in these things are tasked to do some very specific things. And one of those tasks isn't "achieve the best fuel mileage possible". It is a balance between achieving operating temperature, maximizing power, drivability, comfort, etc.
As a example, one of the truck show that runs the "Ike Gaintlet" was quite frustrated with the new GMC 2500 or 3500 because I'm tow haul mode, the transmission was not smart enough to keep the engine in the peak power range. As a result, the truck would hit the desired speed and wid slow down as the RPMs fell. It would finally shift to a lower gear and accelerate back up to the desired speed. This cycle continued all the way up the hill. Ms the speed drop off was 10 to 15 MPH. A person could easily fix this by shifting the tranny to the appropriate gear and hold the same speed all the way up the hill.
