It is a classic mistake to limit the "freewheel" to a fairly steep descent.davcom wrote:+ 1 with Capt_Maloche except for freewheeling. Unless the 307 HDi is different than the DCI, roll freewheeling consumes more than roll in engine braking ... How to be convinced, ride the engine brake downhill and note the conso instantannée ... On my HDi 70 engine brake I arrive at 0,01L / 100Kms in conso instantannée ... And while maintaining the same speed, go freewheeling. When I did the experiment, at 90KM / Hr the instantaneous conso told me about 1L / 100KMs coasting ...
Indeed, all the recent engines (common-rail injection) have an injection cutoff in deceleration. So effectively, if the slope is sufficient to keep the speed, the freewheel makes more consume (between 1.2 l and 0.5 l according to the speed).
What Maloche mentions is anticipation before stopping (which can also be done downhill before attacking a lift, or on a weak slope). If you stay on the engine brake, you lose momentum and you have to go throttle, while if you are coasting, you continue on your momentum and you consume just enough to maintain the idle.
On modern diesel, it's quite subtle, you really have to know his car to know where and when to coast.
On older cars, no question to ask: the freewheel makes real economy!
The injection is even completely stopped in engine braking: it is the wheels that turn the engine and not the other way around.davcom wrote:In my opinion the injection is minimal in engine braking or deceleration after downshifting because no need for much fuel to run the engine, it rotates thanks to the inertia of the vehicle through the transmission. On the other hand in freewheeling it must turn to the combustion ... From where the remark earlier than a vehicle at the stop 3mins consumes as much as a vehicle on 1KM to 50KM / Hr;)