....this will upset a few people and burst some bubbles:

http://www.carbuzz.co.uk/blog/New-Skoda-Octavia-Review-461

Notably the paragraph:

"The car also "coasts" in Eco mode, decoupling engine from transmission when you lift off the throttle pedal. Should you brake, it then re-couples to provide you with engine braking. It's effective, unintrusive and no doubt contributes to that excellent economy figure, as does standard stop-start on all models."

So, according to Skoda, it's more economical to disengage engine from drive-train (rather than allow the "over-run" thing). I suspect the research that went into this will be more than the "over-runners" will have ever been able to do :p :p :p

I thought it was illegal to coast without the engine/drive engaged to each other?

As for the overrun thing - VCDS records an injector duration of 0ms on my Polo - I don't see what's more economical than that? (Unless it creates petrol?!)

I assume it'll be because though your car isn't using any fuel the engine is slowing the car quicker than if it's coasting so you have to reapply the accelerator quicker and so start using fuel again when the 'other' option will still be off the throttle and using no fuel in a similar situation.

If it indeed coasts diesel engine a lot to save fuel, I suspect it is a product of having the damn DPF on board. Engine braking cools down DPF (lots of air run through it), which then needs extra fuel to get back to operating temperature.

In any case, yet another gimmick that will no doubt make fuel economy and CO2 rating look great, while doing the opposite to total cost of car ownership from purchase to scrap.

Running stuff off the battery a bit like a stop-start but moving? Seems a little odd since injection is basically off if you're off the throttle. If it's running off a big battery while coasting that'll need recharged when you're back on the gas.

One of those things that works well in the emissions test if not in the real world?

One can only assume someone has done the sums on keeping an engine at idle versus the energy "lost" (momentum) from engine braking?

..and it will all be undone as most drivers will expect the car to slow down more when you let your foot off the throttle...and brake...

As for the overrun thing - VCDS records an injector duration of 0ms on my Polo - I don't see what's more economical than that? (Unless it creates petrol?!)

If you want to feel what an engine feels like when there is actually no fuel being injected take the car to the top of a hill, switch the ignition off, switch it back to I (usually the accessory position, but no ignition), put it in neutral, start rolling down the hill. When you hit 20mph, drop it into gear (any gear will do). You are now experiencing an engine with no fuel. Let us know how far/fast you go.

Running stuff off the battery a bit like a stop-start but moving? Seems a little odd since injection is basically off if you're off the throttle. If it's running off a big battery while coasting that'll need recharged when you're back on the gas.

Why would it be running only off the battery? It's dis-engaging the clutch, not the alternator. And let's face it, this isn't going to be active for miles and miles.

If you come off the throttle, which should then shut-off the injection, and then hit the clutch, shouldn't the revs hit zero -or- shouldn't you feel the starter kick-in again to restart the engine? (Just like stop-start)

Also, if you take your foot off the throttle and allow over-run to shut-down the injectors, why does pressing the brake the do the same? (Hence you can't left-foot brake an Octavia* {unless you been Sharked }) I seem to recall (and will try and find the reference for this) that pressing the brake pedal drops the fuel flow to the engine to aid braking. Surely VAG wouldn't R&D redundant system like this. Would they?

*I don't know about Fabias etc, but I have tried left-footing the Octavia. Before you've even got pressure into the brakes you can feel the fuel-flow drop. As far as I know, the brake-light switch (which also dis-engages the cruise control) is activated before you get pressure into the braking system.

I thought like others if you are off the throttle but in gear coasting the car used no fuel but the engine is turning over just through the momentum of the car. So you get xRPM, and all your electricals but no fuel used.

If the clutch is disengaged/decoupled when coasting either the engine has to run at low rpm to keep all the pumps etc running or they have to be run by another power source. Seems strange that running the engine even in neutral is more economical than it running without fuel. Plus if it's decoupled from the wheels is there some electronic wizardry to raise and lower the revs or going downhill at 70 is the engine going to continue to run at ~4k rpm but in neutral.

Just sounds odd.

And you're right you can't brake and accelerate in the Octy which is pain in the arse if you'd like to dry your brakes after going through a flood. Another one of these bloody aids that don't really help.

You can brake and accelerate, but only until ~1200rpm, above this rpm fuel will be cut. So put it in 1st/2nd and try again from idle.

Or you can press brake and accelerator and see 1200rpm governed (note it was 1200rpm on 1.9, perhaps new engines chose different rpm number).

Re coasting in Eco mode, in real life driving you take foot off accelerator when you want to slow down.

Engine braking is welcome then. I predict people using brake pedal a lot more with this "Eco" feature, and near-zero impact on fuel economy in real life.

For DPF equipped diesels, to genuinely save fuel in mixed driving (by keeping DPF hotter), it probably would make more sense to forbid engine braking altogether until emergency braking requested, or until the car is driven at a low speed (resulting in low rpm). Uprated brakes would be required.

Old skool hydraulic convertors effectively coast when you lift off - ever tried engine braking with one?

Does the left foot braking thing also apply to manual petrol turbos? I mean I'll find out tomorrow as haven't tried it yet, not that its *that kind of car.

Old skool hydraulic convertors effectively coast when you lift off - ever tried engine braking with one?

Does the left foot braking thing also apply to manual petrol turbos? I mean I'll find out tomorrow as haven't tried it yet, not that its *that kind of car.

Does on my TFSI anyway. I don't know about the rev limit or anything like that, I only know I've been unable to brake gently after going through deep water.

Same on the Mk2 Fabia vRS - most annoying as when its raining you need a double press to get any brakes...

Now I know my Mercedes make such a bit thing about it...

I think Audi have been using this technology for a while.

Sent using whatever device I'm using at the time.