Today I Am Driving . . .

I'm glad you've brought that point up, as this is something I've been wondering about for a while - do ECU controlled diesels do this as well as petrols?

Would my Lynx engined 1.8TDi Fiesta (75PS) do this (i.e. use zero fuel due to a cut-off switch/relay on deceleration).

In response to DervBoy - I make myself benefit from the lack of much engine braking by being able to come off the acclerator earlier on approach to junctions as I know it'll decelerate less. This has surely got to be saving fuel. It also means that if it has slowed down a bit more than I wanted I can just gently press the accelerator pedal again, without having to put the thing back in gear.

Peter

Reply to
AstraVanMan
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But as I explained, the lack of engine braking is brought about by the absence of fuel cut-off on the overrun. Therefore you cannot be saving fuel.

The reason my Astra DTI does have engine braking is because it _does_ cut off the fuel on the overrun.

My previous petrol astra did have lots of engine braking before it was "upgraded". Afterwards it didn't. How can this sudden change in engine braking be achieved any other way than disabling the overrun fuel cut-off? Average fuel consumption before the ECU upgrade was 44mpg. Afterwards it averaged only 40mpg. Draw your own conclusions from that.

The Dervboy

Reply to
DervBoy

Not true, many newer ECUs hold fuel beyond cutoff for a period for emissions reasons which I hope someone else can explain. Compare a 5yr old snappy K series with a current one.

Reply to
Tim S Kemp

Chickened out ? Even a Cav GSi will only just nudge over 130mph, hardly pant cacking speed.

Probably just not noticing it due to the bigger engine...

Reply to
Lordy

I fail to see how delaying the over-run cutoff can reduce emissions. Surely; no fuel = no emissions?

And what's a "snappy" K series? I've never driven or worked on a car with a K series engine.

cheers The Dervboy.

Reply to
DervBoy

Not quite. Less fuel = incomplete burn = more emmissions.

The older less strangled versions, I assume.

Reply to
Lordy

No, but very licence threatening, especially in suffolk where the pigs and councils think the whole county should be reduced to 30mph. I generally stay below 95. And the pigs always "hang out" on the trunk roads round here, not in town where speeding poses a genuine danger.

I never noticed it on the 1600 petrol either. But on both cars it is obvious when I turn the switch on or off, so I'm sure I would have noticed if it was turning itself on and off.

The Dervboy

Reply to
DervBoy

Read carefully my post. It says _no_ fuel. This is the situation in overrun cut-off, like all eary EFI systems. I would be curious to know how attempting to burn zero fuel can create any exhaust gas. In this case, input = output, i.e. atmospheric air.

"Less fuel" is what you now get with these new systems which introduce the overrun cutoff gradually. So surely according to your formula above the new way increases emissions?

I see now.

The Dervboy

Reply to
DervBoy

heh I remember driving a Fiat Bravo 1.6, under 8 miles on the clock, 100mph third gear...

Reply to
Tim S Kemp

Mee too, but that was rover's excuse for the new cutoff profile on the K series

Original K series motors were very snappy, rev like mad, die instantly. Lovely to drive and a snarly intake note, could be thrashed continually as long as there was oil and water in the right places. Then they changed the ECU mapping and they hold on to the revs when you release the throttle instead of dropping straight away.

Reply to
Tim S Kemp

I changed the wording deliberately. _no_ fuel would equal stall, surely...

Reply to
Lordy

Fuel is then supplied under a certain number of revs. So no fuel when decellerating.

Reply to
Tim S Kemp

No, it's because the Ka is such a damn sexy beast on wheels to the discerning lady in point. :)

Reply to
DervMan

Almost! About 87 or so indicated in third. That's at 7,000 rpm and it's still pulling. :)

I'm a bad boy.

continually.

Ford ECUs have a ten second timer: you need to select full power for ten seconds for the air conditioning to shut down. Of course, the number of times that you actually have full power selected for ten seconds or more is limited, to say the least. /cough/

You do get used to it, though. I recall my Cinquecento: when you lifted off the accelerator pedal, she just about stopped!

The Mondeo, in comparison, took forever to stop - a combination of superior aerodynamics, lots of weight, and that cunning spring assembly that took several seconds to shut the power off.

The Ka's ECU doesn't shut fuel off immediately, but it's cunning in that it squirts fuel into the donk so as to save the trees. It takes a few seconds to stop squirting fuel. Curiously enough, having gotten used to how quickly he decelerated with a binding brake, now he seems to go on forever . . . :)

Wahey! So, it was a proper upgrade, heh!

Nah, she's perfect.

Reply to
DervMan

Yes, this is true in theory, however you're left with an incomplete burn, which causes harmful emissions. I don't pretend to understand how or why, but it's true of both petrol and diesel variants - this is why the Ka's fuel cut off takes several seconds.

Keeping the driver smooth isn't a priority.

It's merely that the older models have a much more aggressive cut off switch.

I've not driven a Golf recently besides the appalling 1.6 I borrowed a couple of weeks ago, and that did it: as soon as you lift off or hit the brake pedal, it stops fuel petrol into the donk. However, it does it with a jerk. A clunky jerk. Then, when the revs reach 1,600 rpm, there's another jerk as it starts squirting fuel into the engine once more. It feels appalling. You can get it to kangaroo if you are descending a gradient in gear, off the power, with the donk churning over at the 1,600 rpm level.

Of course, if you are reasonably careful and smooth, you tend to drive about town at this engine speed, so I find the Golf to be an extremely jerky frustrating piece of kit.

Mind you, I hated them before I found this out. I kinda take pride in being smooth, but I can't be smooth in a Golf in town (and I couldn't be smooth in a 1.25 Fiesta with the air conditioning running, too).

Reply to
DervMan

Deep down I knew you weren't a disloyal person. Perhaps your discerning partner would also come to appreciate a Mondeo TDCI, if she spent a weekend driving one :-p

The Dervboy

Reply to
DervBoy

yep - makes heel/toe impossible as it won't fuel while braking!

Reply to
Tim S Kemp

The trouble is that she kinda likes the look and "cute fuzziness" of the Ka. I can see her point. You see, the Ka does have faults, but it has a certain chic, a certain charm. It's simple inside, everything falls to hand. It's pointy-steery at sensible speeds, it's comfortable, and it still looks fresh and modern.

Sadly, and I really do see Charlie's point, because we're in a courtesy Fiesta this weekend. Now the Fiesta has the 1.25 litre engine, which is a real gem of a donk, and it has a larger interior, but it lacks the Ka's charm. It looks dull, both inside and out, and although it's pokier, it lacks a something.

And when she sees the Mondeo, she says, "might be a nice car, but it doesn't make me want to drive it."

Reply to
DervMan

How can the engine stall if the vehicle is in gear, clutch engaged and moving at considerable speed?

They prevent stalling by reinstating the fuel supply as soon as the engine speed drops below a certain point, typically this was around 1400rpm. So if it's in gear, doing 70mph which is say 2700rpm, and no throttle, no fuel whatsoever is injected. As the car slows down and the revs eventually drop below the threshold of 1400rpm, the ECU returns to the idling fuel mixture, thus preventing stalling.

On many recent vehicles, judging by the lack of engine braking, this feature would appear to have gone amiss.

The Dervboy

Reply to
DervBoy

I find I can drive perfectly smoothly in almost any car except those which try to be clever. The Astra DTI is really nice in town, with good observation I rarely touch the brake except to come to a complete stop. The Astra 1.6 was also like this before it was tampered with. You would get the on-off effect you describe when descending a hill at low speed, but it was well damped so it didn't jerk. Afterwards I couldn't drive smoothly because I had to keep going for the brake pedal.

I guess my skill in clutch and throttle control came from learning to drive in a 15 year old cortina which had done 260,000 miles, had an on-off clutch, about 1/2 a turn of play in every drivetrain component, a stiff throttle cable and knackered rear axle mounting bushes. I did a much better job of it than my dad!

The Dervboy

Reply to
DervBoy

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