2.0Ltr HDi, is the fuelling shut off when on the overrun?

[ghost123uk]

No problem here, just curious.

I know on some other modern cars, when going downhill, in gear, but with no throttle applied, ie on the "overrun", the fuelling is shut off completely to improve the MPG.

Does anyone know if an 05 plate 2.0Ltr HDi, does this?

[ron]

Yes it does.

[ghost123uk]

Ta for that ^^^

I should stop trying to save fuel by coasting down the hills then
Just stick it in 5th gear and take my foot off the gas

[ron]

Ta for that ^^^

I should stop trying to save fuel by coasting down the hills then
Just stick it in 5th gear and take my foot off the gas

Coasting is so yesterday & uses fuel.

[ghost123uk]

No problem here, I just like to know stuff.

Yesterday I did some tests on this on some of our local country B roads.

OK, so your going  down a hill at about 30, in 4th, you have your foot off the throttle, all well and good. However, when the decent down the hill ends and there is a flat stretch, the car will keep going along, with no foot on the throttle, at it's tick-over RPM.

Question, how does it "know" when it's going downhill (or on a de-accelerating overrun) so it can shut the fuel off? (compared to trundling along on the flat, no foot on the throttle, at tick-over rpm)

[Arfcollins]

I wouldn't think it does cut the fuel off completely, there will always be the tickover level if your foot is off the throttle, whether you are going downhill or just slowing down.

[ghost123uk]

Well that's what I was thinking, but Ron is very rarely wrong in such matters.

What do ya reckon Ron?

[ffrenchie]

Coasting is going to cost exactly the same as leaving it in gear even if it doesn't cut the fuel and you are losing the benefit of engine braking so you are not in full control of the vehicle. I know the BSI is doing something to the throttle as when I am in traffic inching along when the engine is ticking over in first or second gear and gets close to stalling it actually speeds up the tickover to prevent it. The car is already doing 50ish mpg driving normally, what is the point of coasting ?

[ron]

Well that's what I was thinking, but Ron is very rarely wrong in such matters.

What do ya reckon Ron?

I stick by my opinion.With throttle off & on overrun the system shuts off the fuel & when throttle applied or overrun ceases ,fuel is fed again.You don't have to believe li'l ol me.The info is out there.This has been happening since the 80's on injected petrol cars as well.I retired,10 years ago, after 40+ years in the trade & did pick up little snippets on the way.

[ron]

Coasting is going to cost exactly the same as leaving it in gear even if it doesn't cut the fuel and you are losing the benefit of engine braking so you are not in full control of the vehicle. I know the BSI is doing something to the throttle as when I am in traffic inching along when the engine is ticking over in first or second gear and gets close to stalling it actually speeds up the tickover to prevent it. The car is already doing 50ish mpg driving normally, what is the point of coasting ?

That's why you can move from stationary with a diesel using no throttle.As you say,it's a handy thing in traffic.