[tyler durden]

yes the accel is great, but just discovered the engine braking effect when coasting. Niiiice

[zltm089]

hmmm...i don't really think its that nice!.. considering its using petrol when downshifting.

I would prefer if the automatic downshifting "engine" braking, activates when I start applying the brake, then it would keep the revs high and reduce the amount of braking required (although it does drink petrol when downshifting, at least i know i'm saving on my brake pads! lol)....but not when I let the car roll/ coasting, driving in economy style mode! lol

when I was driving manual cars, to "save" petrol, I used to let the car on neutral on long stretches until the next set of traffic lights lol.....but with auto gearbox now...as soon as I let go of the gas, the car slows down!....

anyone welcome to correct me if i'm wrong...

[RCUK]

putting it in neutral on a manual car doesnt save petrol!

Leaving it in gear and coasting to the lights does!

[zltm089]

maybe...

but my understanding was that if i let it roll in neutral...car is not reving at all...(well 1000 rpm approx) ,....and letting the speed decrease slowly... then this would be saving petrol and my brake pads since i'm not "touching" the throttle nor the brake pedals....

but leaving the car in gear would slow the car down well before i can make it to the traffic lights and it would be reving at about 2-3000 rpm....(if in, lets say 5th gear)

[tyler durden]

TBH not really bothered by the petrol issue.

Just like the way is slows down if you take your foot off the accelerator. There is a slight urgency about it.

[hmi1750]

its not good to coast out of gear in a manual car, if you had to make a sudden manoeuvre you would have little control on the car in terms of speed or having it in gear to accelerate away. In fact it could even stall if you try to put it into gear.

On the note of engine breaking in DS, i use it all the time in the 330d coming when braking hard from high speeds and also to maintain better control doing down hills.

It can over rev though if accelerating away so I just change back to D.

[RichardM]

Originally Posted by hmi1750

It can over rev though if accelerating away so I just change back to D.

Is this just a problem with diesel and DS? Petrol motors may be fine as they will happily rev to the read line.

[xenon]

It won't use petrol in this mode - on the overrun the DME reduces the fuel supply to the minimum required for the engine to fire. With the momentum of the car turning the engine it would use less fuel than taking it out of gear and letting it idle.

[doughboy]

Originally Posted by zltm089

maybe...

but my understanding was that if i let it roll in neutral...car is not reving at all...(well 1000 rpm approx) ,....and letting the speed decrease slowly... then this would be saving petrol and my brake pads since i'm not "touching" the throttle nor the brake pedals....

but leaving the car in gear would slow the car down well before i can make it to the traffic lights and it would be reving at about 2-3000 rpm....(if in, lets say 5th gear)

zltm089, in an old carburettor petrol engine you are right that the engine still uses fuel on the overrun (thus pops and bangs from hot carb engines on overrun)

On a modern road car injection engine on idle (coasting in neutral) it is using petrol to keep ticking over, but when you take your foot off the gas on overrun the ECU will stop all fuel until the engine reaches idle or you put your foot on the gas again.

So coasting in gear down towards idle speed uses ZERO fuel.

[zltm089]

Originally Posted by doughboy

zltm089, in an old carburettor petrol engine you are right that the engine still uses fuel on the overrun (thus pops and bangs from hot carb engines on overrun)

On a modern road car injection engine on idle (coasting in neutral) it is using petrol to keep ticking over, but when you take your foot off the gas on overrun the ECU will stop all fuel until the engine reaches idle or you put your foot on the gas again.

So coasting in gear down towards idle speed uses ZERO fuel.

cheers for the heads up mate!...see your point!...well described argument...

[dxb335d]

Engine braking does not use any fuel... fuel is cut off on the over-run.

[dxb335d]

ooops... Someone has already explained.