MPG on Overrun/no fuel cut off

[Bendelaurence]

So, another daft bendelaurence topic

Pretty much every car I have owned young enough to be injected with an ECU have had fuel cut off on overrun. You're driving, you take your foot off the accelerator, and MPG goes to -.-- mpg, until the revs drop to about 1000rpm, at which point stall prevention kicks in and the ECU starts feeding some petrol in again.

The first thing I noticed in my car (in comfort mode) is that when you take your foot off the accelerator it seems to 'roll' very well on overrun. I put this down to the car being heavier, and maybe better bearings or something. But...... Today I noticed that when I take my foot off the accelerator on a relatively flat road, the consumption remains at about 40-50mpg at about 2000rpm. The only time it doesn't do this is in dynamic mode, where you get the expected -.--mpg, but the revs are higher because its holding a lower gear.

Is this normal? It seems crazy to have the engine outputting some power to the wheels with your foot off the accelerator. Using more fuel, and more expensive brake liners for no reason. Its like an old automatic with a slush box, which we all know went through way more brake pads than a manual. S-tronic is essentially and manual gearbox with hydraulic clutches (correct me if im wrong). So again, im wondering if I have another problem...

Whats your experience?

Ben

[innercry666]

Hi Ben,

In a word, 'Yes' it is normal. It's covered in the manual, but effectively it's fuel overrun. I don't remember specifically what it says but I used to lift and coast a lot when on 30 sections of road as you would effectively 'roll' along way before starting to loose speed as there is still fuel being injected.

Hope that helps.

[Bendelaurence]

Any idea why they do this? I watched it a lot driving today. Tbh it does it a lot less than I first thought. But still, for what reason would they make you brake against the engine. I don’t see a reason for them not programming it to cut the fuel and downshift. I reckon that would have lead to some substantial mpg gains when driven conservatively...

[noddy]

I have a similar issue, when driving around town it would be nice to have more engine braking as standard, rather than the coasting it seems to do. I always seem to be on the brake. TBF, this is the only compromise, on open roads you don't notice it. In manual you can control it much better, and it detects and does cut fuel quicker.

[Bendelaurence]

I have a similar issue, when driving around town it would be nice to have more engine braking as standard, rather than the coasting it seems to do. I always seem to be on the brake. TBF, this is the only compromise, on open roads you don't notice it. In manual you can control it much better, and it detects and does cut fuel quicker.

It’s nit just me then. I suppose we can’t have it all. There must be a reason for it, seems like a very obvious oversight if not.