Coasting in neutral, good idea or bad?

Wig

pault123 wrote: »

Would this indicate the automatic models working differently with the overrun?

Or an ommision left in the manual?

My old Nova used to have overrun and that was 87! I really can't see why a modern Corsa wouldn't have it.

Maybe it refers to diesel engines?

cyclonebri1

Its as I said it's the ECU fueling the car by the means mentioned above to take account of the slight load thats being applied. I assume it does this at very low speeds ie around 3/4mph as it is below the lower threshold of speed sensing and so the ECU thinks the car is stationary and so applies additional fueling.

Provided the engine is not juddering or approaching stall I wouldn't expect it to do any damage.;)

cyclonebri1

Wig wrote: »

This is the throttle control or idle control keeping it going. Nothing to do with overrun.

Apparently the way to test for overrun is to drive at 30mph come off the foot pedals and allow the car to slow down, when it goes below 1100 - 900 rpm it will suddenly spring into life as the fuel goes in.

:rolleyes: :rolleyes:
The ECU controls the lot, yes by the idle control, but under both anti stall and fuel shut off conditions (overrun). Both the fuel and air inlet are closed on overrun.;)

tomstickland

Automatic cars do have to work differently. IIRC there's no ability for the overrun - the car cannot drive the engine due to the way that automatic gearboxes (don't) work.

Pew_Pew_Pew_Lasers!

Eh? Mine is an automatic and cuts fuel on overrun and braking.

pault123

loofer wrote: »

I was going to start a new thread on this but I guess there's quite a few knowledgeable folk here.

My car (and I'm guessing this could be common with other of diesel cars) can move along in 1st gear without me even touching the accelerator. The rev meter will read about 1000rpm whilst moving. I would only do this in extremely slow moving traffic and would lift the clutch pedal slowly to prevent stalling.

Could this be causing any damage to the clutch/flywheel/engine or other parts/components??

Clutch wear occurs in the slipping phase, ie the position between fully pressed or fully depressed.

The only gear the slip takes time is moving off in first gear, 2nd upwards is quite a fluid motion. (unless bad habits such as rocking on the clutch to hold the car on a hill are used)


How much longer does it take to slip the clutch when no revs are used?

For example if it takes twice as long to lift your foot - twice as much wear occurs?! just a thought.

Wig

cyclonebri1 wrote: »

:rolleyes: :rolleyes:
The ECU controls the lot, yes by the idle control, but under both anti stall and fuel shut off conditions (overrun). Both the fuel and air inlet are closed on overrun.;)

I was just confused why, when we were talking about overrun, you started your post talking about overrun, then said "try crawling up a hill" as though it was something to do with overrun.

pault123

Wig wrote: »

This is the throttle control or idle control keeping it going. Nothing to do with overrun.

Apparently the way to test for overrun is to drive at 30mph come off the foot pedals and allow the car to slow down, when it goes below 1100 - 900 rpm it will suddenly spring into life as the fuel goes in.

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. Revs usually sit around 1800-2000. IF they do drop to 1100-1000 I usually give the revs a tap to keep me going. I've never tried dropping to 900 as the engine starts to sound quite unhealthy around this range.

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?

A car equipped with overrun, would give itself the fuel at the appropriate time, it would sound unhealthy depending on where your ECU sets it's lower limit. It shouldn't stall, it would be effectively a controlled "bump start". Although if you are in a gear higher than 2nd, there could be a stall because you would be going too slow for that gear to be effective. Unless the fuel is injected at a higher revs because the ECU senses the impending stall somehow.

cyclonebri1

Wig wrote: »

I was just confused why, when we were talking about overrun, you started your post talking about overrun, then said "try crawling up a hill" as though it was something to do with overrun.

Sorry for the confusion, just trying to get accross to others what a range of work the engine ECU does in a modern car;)