Is it true

[Burnerman]

WOTAN
Are you refering only to diesel engines ?

I believe the combination of speed / movement sensors plus the throttle position sensor gives info to the ECU to shut off power to the injectors on both types of engine - simple enough as all injectors are operated by solenoids these days.
John

It would also have to know the clutch was not depressed, via some sort of micro switcc

I just cannot envisage, for reasons of safety, that the fuel would be cut off completely, be it petrol or diesel, I stand to be corrected on this one if there is a definitive answer.
The economy gauge on my BMW when on the overrun, goes full scale indicating more than 80 MPG is being achieved, at no time do I get the impression that the engine is not producing some power.

I've really no idea for sure, but when my Skoda vRS had this live data check, the guy alongside with his lap top said that the injectors were passing no fuel when coasting downhill.....the fuel computer just had --- on the display. With the slightest touch of throttle, this gives a reading of around 180 MPG.
John

 

[nickso]

K-Jetronic I think

There was a big diaphragm controlled by a big weak spring, which was sucked a distance dependent on the mass of air travelling into the engine, which moved a needle valve metering the petrol flow

K Jetronic? A la the Escort XR3i? I thought Audi would have moved on.
Don't know though.
John

thats k-jet. bosch designed it and loads of maunfacturers used it. it was prone to many issues hence L-jet arrived and i think motronic after that.

thankfully L-jet did away with the plate arrangement and is very reliable. i've got two cars runing on L-jet and motronic and one that used to.

 

[Biguns]

it realy must be true for all cars manufactured from the mid to late 80s

http://www.toyotaownersclub.com/forums/lofiversion/index.php/t633.html

 

[Mickymoody]

It must be true because Jeremy Clarkson said it is the most ridiculous thing I ever heard in my life!

If an engine is starved of fuel, regardless of it's delivery method, then the engine will stop. That's why fuel exists, to power the engine.

If Jeremy Clarkson invented another method of powering an engine, I'd be the first to disbelieve it.

What he is talking about is the vacuum method of an engine, if you go down a slope in 1st, in a carpark, and don't touch the accelerator pedal, then the car automatically brakes, by using the engine as a brake, but the vehicle still uses fuel, otherwise the engine would not run.

 

[Biguns]

It must be true because Jeremy Clarkson said it is the most ridiculous thing I ever heard in my life!

If an engine is starved of fuel, regardless of it's delivery method, then the engine will stop. That's why fuel exists, to power the engine.
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Sorry but you are wrong. If you parked a car on a hill with the ignition switched off,released the brakes (lets forget the the steering lock for the moment) then put it into gear say 4th The engine would start turning at a speed dependant on the gradient, the weight of the car, which gear it was in. and the speed at which the clutch was released.This is without any fuel being introduced. This situation would continue till the compression effect of the engine overcame one of the above conditions and the car would stop.
I think that with the documentary evidence we have , we must accept (Clarkson aside) that this feature does exist in all/most modern cars.
In my past life I worked in very heavy commercial vehicle (Crane) manufacture. In the 1970s we fitted these machines with exhaust brakes for down hill speed retardation. When going downhill in gear, the driver would take his feet off the accelerator and clutch, and press a button on the floor with his foot, this would then shut off the fuel to the engine and a flap would practically close the exhaust manifold. Thus in effect turning the engine into a compressor, retarding the cranes progress. On the heavier cranes fitted with the Cummins diesel engine the fuel was cut and a cylinder head mechanism stopped the valves from opperating, this system was dramatically effective as an engine brake

 

[Mickymoody]

It must be true because Jeremy Clarkson said it is the most ridiculous thing I ever heard in my life!

If an engine is starved of fuel, regardless of it's delivery method, then the engine will stop. That's why fuel exists, to power the engine.
-------------------------------------------------------------------------------------

Sorry but you are wrong. If you parked a car on a hill with the ignition switched off,released the brakes (lets forget the the steering lock for the moment) then put it into gear say 4th The engine would start turning at a speed dependant on the gradient, the weight of the car, which gear it was in. and the speed at which the clutch was released.This is without any fuel being introduced. This situation would continue till the compression effect of the engine overcame one of the above conditions and the car would stop. I think that with the documentary evidence we have , we must accept (Clarkson aside) that this feature does exist in all/most modern cars.
In my past life I worked in very heavy commercial vehicle (Crane) manufacture. In the 1970s we fitted these machines with exhaust brakes for down hill speed retardation. When going downhill in gear, the driver would take his feet off the accelerator and clutch, and press a button on the floor with his foot, this would then shut off the fuel to the engine and a flap would practically close the exhaust manifold. Thus in effect turning the engine into a compressor, retarding the cranes progress. On the heavier cranes fitted with the Cummins diesel engine the fuel was cut and a cylinder head mechanism stopped the valves from opperating, this system was dramatically effective as an engine brake

Highlighted in bold is what I said, there is NO FUEL introduced, the engine acts as a brake, and the engine won't work. So how am I wrong if you agree with me?

Engine braking is demonstated when going down a ramp, with the engine running normally, select 1st, don't touch a pedal, the car descends slowly, and doesn't run away, as it uses the engines compression to halt the car..

A highly effective way of stopping a car from running away with faulty brakes when parked is to select a high gear, if the brakes fail, the engine compression holds the car steady.

However, if 2nd is selected, and ignition is on, then a 'bump' start can be achieved, as the ignition components have power.

So why say I'm wrong, when you agree with me?

 

[big-all]

ok simplistic terms here [correct me if i am wrong ]

the engine governor[engin electronic manigment]requires minimum revs
providing coasting or braking keeps the revs above minimum required there will be little or no fuel input

its much better to let the engine idle and use the road conditions and gradients to reduce your speed within sencibile limits reading the road ahead
on older cars the fuel never stopped it just reduiced to a low level untill the engine revs drop below a level where the fuel needs to added to increses the revs

 

[Mickymoody]

If an engine is turned off, then no fuel delivered. Unless by a manual fuel pump, and then still not ignited, as there is no electrical system to install a spark to the fuel..

So people are STILL unable to READ posts correctly.

 

[Biguns]

It must be true because Jeremy Clarkson said it is the most ridiculous thing I ever heard in my life!

If an engine is starved of fuel, regardless of it's delivery method, then the engine will stop. That's why fuel exists, to power the engine.

If Jeremy Clarkson invented another method of powering an engine, I'd be the first to disbelieve it.

What he is talking about is the vacuum method of an engine, if you go down a slope in 1st, in a carpark, and don't touch the accelerator pedal, then the car automatically brakes, by using the engine as a brake, but the vehicle still uses fuel, otherwise the engine would not run.

The original post was about whether, modern cars, on over run, have a feature which shuts off the fuel, which now appears to be true.
Your post -above- seems to poo poo this.
Therefore it is wrong

 

[daneski88]

Yeah snugib but no but yeah but no But you agree with him and then disagree with him when he has agreed that you disagreed with what you have disagreed with. And we all know what 3, er 4, er 2 wrongs don't make

 

[jetex]

Modern cars do indeed have a system called overrun fuel cut off. The ECU gets information from the speed of the road wheels, the engine revs and the position of the accelerator pedal. If the vehicle's speed is high, but the pedal is not being pressed, it deduces that the vehicle is going downhill and cuts off the fuel injectors for economy and better engine braking. When the engine revs drop to a certain limit, the ECU switches the fuel injectors back on to prevent the vehicle from stalling.

 

[Mickymoody]

It must be true because Jeremy Clarkson said it is the most ridiculous thing I ever heard in my life!

If an engine is starved of fuel, regardless of it's delivery method, then the engine will stop. That's why fuel exists, to power the engine.

If Jeremy Clarkson invented another method of powering an engine, I'd be the first to disbelieve it.

What he is talking about is the vacuum method of an engine, if you go down a slope in 1st, in a carpark, and don't touch the accelerator pedal, then the car automatically brakes, by using the engine as a brake, but the vehicle still uses fuel, otherwise the engine would not run.

The original post was about whether, modern cars, on over run, have a feature which shuts off the fuel, which now appears to be true.
Your post -above- seems to poo poo this.
Therefore it is wrong

An engine CANNOT run, if it devoid of fuel or air. Otherwise you just invented the best engine in the world! A human cannot exist if devoid of fuel or air. What are you talking about?

I agree that in overrun, the injectors use limited fuel, but using no fuel isn't an option, otherwise the engine would stall, and require a bumpstart to restart it, and would kill the CAT, due to unburnt fuel in the system.

 

[Biguns]

Oh dear
Look here, under coasting or gliding."the fuel is cut" not limited
http://en.wikipedia.org/wiki/Fuel_economy-maximizing_behaviors

Look here, under decelerate smoothly. "the fuel is cut off" not limited.
http://www.ecodrive.org/The-golden-rules-of-ecodriving.249.0.html

There woud be no unburned fuel in the system, as the fuel had been cut off, not the ignition

 

[Mickymoody]

Oh dear
Look here, under coasting or gliding."the fuel is cut" not limited
http://en.wikipedia.org/wiki/Fuel_economy-maximizing_behaviors

Look here, under decelerate smoothly. "the fuel is cut off" not limited.
http://www.ecodrive.org/The-golden-rules-of-ecodriving.249.0.html

There woud be no unburned fuel in the system, as the fuel had been cut off, not the ignition

I see no reference to fuel cut off in the Wiki leak, unless it contadicts itself, or is referring to a Hybrid vehicle.

The ecodrive link is tenuous, and makes generalisations, vehicles after a certain date have unspecified electronics that shut off fuel? What are they? Cars before 1990 had ECU's, so can't be that, and it applies to all vehicles or some?

Once again, if an engine doesn't have air or fuel it will stall.

 

[Biguns]

Look at the wiki link again, it's there. In fact Ill help you, here it is for you, with the relevant information in bold and underlined.

Coasting or gliding

The alternative to braking is coasting. Coasting is an efficient means of slowing down, because kinetic energy is dissipated as aerodynamic drag and rolling resistance, which must always be overcome by the vehicle during travel.When coasting with the engine running and manual transmission in neutral, or clutch depressed, there will still be some fuel consumption due to the engine needing to maintain idle engine speed
While coasting with the engine running and the transmission in gear, most car's engine control unit with fuel injection will cut off fuel supply, and the engine will continue running driven by the wheels. Compared to coasting in neutral, this has an increased drag, but has the added safety benefit of being able to react in any sudden change in a potential dangerous traffic situation, and being in the right gear when acceleration is required.

I gave up hard work years ago.