Coasting in neutral, good idea or bad?

cyclonebri1

pault123 wrote: »

Wig we've been discussing overrun as a feature which cuts off fuel with no throttle down a hill, now were talking about it giving fuel when dropping below 1100-900 revs? Would this not stall a car?

To clarify as I roll down hills in gear with no throttle, i've normally picked the most appropriate gear to get me to the bottom without revs.



No it wouldn't. What it will do is cause you to accelarate slightly, or maintain your speed just as if you had touched the accelarator. As soon as the fueling is increased additional air is admitted too;)

Wig

pault123 wrote: »

Wig we've been discussing overrun as a feature which cuts off fuel with no throttle down a hill, now were talking about it giving fuel when dropping below 1100-900 revs? Would this not stall a car?

I tried this the other day, in 5th gear and 2nd gear, both times the car slowed down smoothly - no unhealthy noises or jerking - and eventually the car applied it's own throttle position to compensate and drove smoothly along, I think it did this about 1200 rpm in 5th and 800rpm in 2nd.

So this was not a good way of testing if the car has the overrun fuel cut off feature because there was nothing to suggest that this had occured, the only thing it proved was the car had anti-stall technology - and a throttle position motor.

cyclonebri1

Like what I said, all modern designed cars have this since time gone by. Sorry Wig, not aimed at you, but unless anyones car is ancient, it will behave like this.

This is why we now get closer to 40mph on average than about 30.

OK not a rule but you get what I mean;)

Wig

cyclonebri1 wrote: »

Like what I said, all modern designed cars have this since time gone by. Sorry Wig, not aimed at you, but unless anyones car is ancient, it will behave like this.

But like I said it doesn't prove the fuel was cut off. I also don't agree that all cars would do this, my car has definately got throttle position motor and has no idle control valve. Another car without a throttle position motor and only an idle valve might not cope so well. If anything I reckon it's only the late modern cars that are likely to be able to cope well with this particular test.

This is why we now get closer to 40mph on average than about 30.

OK not a rule but you get what I mean;)

Oh, you mean mpg?

cyclonebri1

Wig wrote: »

But like I said it doesn't prove the fuel was cut off. I also don't agree that all cars would do this, my car has definately got throttle position motor and has no idle control valve. Another car without a throttle position motor and only an idle valve might not cope so well. If anything I reckon it's only the late modern cars that are likely to be able to cope well with this particular test.


Oh, you mean mpg?

Yes, of course I did mean mpg, but like I said you knew what I meant;)

The fuel has to be cut of by giving a zero opening time to the injector(s) from the ECU, otherwise the exhaust will pop and bang on the overun or the fuel will ignite in the exhaust when the throttle is opened again. Both these will quickly destroy the cat.
Late modern cars means almost all new cars since about 1989, thats 19 years ago so not many left without.

Wig

Nope, I don't agree, if the fuel was left on it would ignite as normal in the cylinders.

cyclonebri1

And why would you want to waste money? Modern electronic controls mean you don't have to.

Agree or otherwise but that's how it's worked for many years.

If you can find any modern car that does not shut fuel of on the overun when moving I'll concede the point

Wig

Who said I want to waste fuel? I am just disputing with you that the results of my test prove/disprove/do not show either way.... that the car has fuel cut off feature.


You prove that all modern cars since the late 80s(?) have this feature and I'll concede.

cyclonebri1

Wig wrote: »

Who said I want to waste fuel? I am just disputing with you that the results of my test prove/disprove/do not show either way.... that the car has fuel cut off feature.


You prove that all modern cars since the late 80s(?) have this feature and I'll concede.

By putting fuel into an engine on the overun you would be wasting fuel, it's a general you/we, whether you/we like it or not. It can be designed out so it is.

I never said "all modern cars since the late 80s(?) have this feature " but I did say "most", only because I couldn't give the exact date. I cannot think of any that hasn't. Certainly all catalytic convertor equipped cars are, even ones with single point fuel injection. If the car has a carburettor then it won't be, but then it wouldn't be a modern car . My interpretation of modern may be slightly different from yours, but I can say NO cars produced in the last 12 years waste fuel when it's not needed to keep the engine running

Wig

Fine, that's your opinion. I'm of the opinion that not all cars -with cats- have this. Neither of us can show we are correct.