[di1in]

Originally Posted by longhorn

Sudden acceleration/deceleration leads to excessive fuel consumption not to mention the increased wear and tear on your vehicle. No two ways about it. Ever wondered why you always get better FE on the highway than in the city. That's because we are able to maintain a constant speed for a longer period of time on the highway, which is just not possible in city traffic.

You have misunderstood what I said: When you simply engage a gear in a coasting car (accelerator pedal not depressed) the engine does not consume fuel. The effect that you get here is engine braking.

What you have said is about accelerating a car - when the pedal is pressed - which obviously requires more fuel.

You get better FE while cruising on the highway not just because of the constant speed, but also because you are in a higher gear at a sweeter engine rpm with little swerving. The constant speed just helps the ecu to tune the fuel injection to a slightly leaner mix.

[honeybee]

Originally Posted by m_upreti

Is this in neutral or in gear.

In my Scorpio even I lift my foot off the A pedal, and the vehicle is in geat (say 1st) it continues moving without stalling which shows that the fuel is being fed to the engine ( I have however not tested the distance it would move in this condition, but it does manage to climb a 25 degree ramp without any issues).

Yes, I would like to ask the same question. Recently had an opportunity to drive a diesel Vista, and I can literally feel the car moving forward the moment I release the clutch. It's slow, gradual but it does start moving without any input from the accelerator. The same behaviour was observed as I slowed down for a speed breaker, downshifted to second and the car kept running with all three pedals untouched.

So, does the fuel really not reach the engine if you aren't pressing the accelerator? Or is this specific to the overdrive or otherwise higher gears (which I believe is unlikely)?

[DRIV3R]

Originally Posted by honeybee

Yes, I would like to ask the same question. Recently had an opportunity to drive a diesel Vista, and I can literally feel the car moving forward the moment I release the clutch. It's slow, gradual but it does start moving without any input from the accelerator. The same behaviour was observed as I slowed down for a speed breaker, downshifted to second and the car kept running with all three pedals untouched.

So, does the fuel really not reach the engine if you aren't pressing the accelerator? Or is this specific to the overdrive or otherwise higher gears (which I believe is unlikely)?

This is purely due to the high torque output from the word 'Go' in diesel engines. BTW, without fuel, how do you think the engine keeps idling/running?

[m_upreti]

Originally Posted by honeybee

Yes, I would like to ask the same question. Recently had an opportunity to drive a diesel Vista, and I can literally feel the car moving forward the moment I release the clutch. It's slow, gradual but it does start moving without any input from the accelerator. The same behaviour was observed as I slowed down for a speed breaker, downshifted to second and the car kept running with all three pedals untouched.

So, does the fuel really not reach the engine if you aren't pressing the accelerator? Or is this specific to the overdrive or otherwise higher gears (which I believe is unlikely)?

I think we will need the gurus in the forum to answer and explain this

[SunnyBoi]

Originally Posted by honeybee

Yes, I would like to ask the same question. Recently had an opportunity to drive a diesel Vista, and I can literally feel the car moving forward the moment I release the clutch. It's slow, gradual but it does start moving without any input from the accelerator. The same behaviour was observed as I slowed down for a speed breaker, downshifted to second and the car kept running with all three pedals untouched.

So, does the fuel really not reach the engine if you aren't pressing the accelerator? Or is this specific to the overdrive or otherwise higher gears (which I believe is unlikely)?

I have a Palio and the same happens. From what I've heard, that is the anti-stall of the ECU working. It feeds in little amounts of fuel to stop en engine from stalling. When you release the clutch, load increases and it adds little bit of petrol bypassing the right leg throttle. Result is car moves along, but it never crosses the idle RPM. Its got nothing to do with the torque or power of the engine.

[a4anurag]

Originally Posted by SunnyBoi

I have a Palio and the same happens. From what I've heard, that is the anti-stall of the ECU working. It feeds in little amounts of fuel to stop en engine from stalling. When you release the clutch, load increases and it adds little bit of petrol bypassing the right leg throttle. Result is car moves along, but it never crosses the idle RPM. Its got nothing to do with the torque or power of the engine.

Can you explain more on the ECU part?

I have a Ritz VDi (DDiS engine), What I generally do is revv the 1st gear till 2K rpm which is at 20kmph and upshift to 2nd gear and by the time I release the clutch the car leaps forward and goes till 30kmph without the input from accelerator pedal. I don't think the ECU would be feeding diesel to prevent the engine from stalling and I guess its to do with the Torque of the engine.

Please correct me if I'm wrong. No offences to you or anyone. Just a doubt!

[SunnyBoi]

Originally Posted by a4anurag

Can you explain more on the ECU part?

I have a Ritz VDi (DDiS engine), What I generally do is revv the 1st gear till 2K rpm which is at 20kmph and upshift to 2nd gear and by the time I release the clutch the car leaps forward and goes till 30kmph without the input from accelerator pedal. I don't think the ECU would be feeding diesel to prevent the engine from stalling and I guess its to do with the Torque of the engine.

I think that's the throttle body/something similar sticking open when it should not be. What symptoms you are mentioning again should not happen in a normal car. Suggest you to get it checked at A.S.S

[a4anurag]

Originally Posted by SunnyBoi

I think that's the throttle body/something similar sticking open when it should not be. What symptoms you are mentioning again should not happen in a normal car. Suggest you to get it checked at A.S.S

I have driven a couple of Ritz and swift DDiS and all have this same phenomenon as to what I have described. MASS says its normal and the Service engineer said "Saaar, 190Nm torque is the thing why this is happening. Engine and clutch are fine!"

[longhorn]

Originally Posted by di1in

You have misunderstood what I said: When you simply engage a gear in a coasting car (accelerator pedal not depressed) the engine does not consume fuel. The effect that you get here is engine braking.

What you have said is about accelerating a car - when the pedal is pressed - which obviously requires more fuel.

You get better FE while cruising on the highway not just because of the constant speed, but also because you are in a higher gear at a sweeter engine rpm with little swerving. The constant speed just helps the ecu to tune the fuel injection to a slightly leaner mix.

If the engine is running, it consumes fuel irrespective of whether the A pedal is depressed or not.Period. Whether you are coasting in gear or accelerating only makes a difference to the quantity of fuel being consumed.

[honeybee]

Originally Posted by DRIV3R

This is purely due to the high torque output from the word 'Go' in diesel engines. BTW, without fuel, how do you think the engine keeps idling/running?

Good point!

Originally Posted by SunnyBoi

I have a Palio and the same happens. From what I've heard, that is the anti-stall of the ECU working. ... Its got nothing to do with the torque or power of the engine.

I observed the same behaviour in a Premier Padmini diesel. I don't think it had an ECU. So I doubt if it's the ECU at the core of this phenomenon.

Originally Posted by longhorn

If the engine is running, it consumes fuel irrespective of whether the A pedal is depressed or not.Period. Whether you are coasting in gear or accelerating only makes a difference to the quantity of fuel being consumed.

That sounds logical.

[me_sid]

The padmini was in a good state of tune my friend ( those days the good ol friendly mechanic used to tune it by hand remember). The engine doesnt stall because off course the tourque and the fuel regulation is done by your cars brain, thats ECU. In a MHAWK scorp or for that matter any diesel car u can shift to 2nd gear even to 3rd without knocking or stalling ( without pressing A pedal). And @Longhorn is right .

[di1in]

Originally Posted by longhorn

If the engine is running, it consumes fuel irrespective of whether the A pedal is depressed or not.Period. Whether you are coasting in gear or accelerating only makes a difference to the quantity of fuel being consumed.

Originally Posted by honeybee

That sounds logical.

Perhaps you have read it out of context. This is how the discussion progressed:

Di1in said: Simply engaging a gear while the car is coasting should not induce rapid fuel consumption because even if the rpms climb rapidly for a second or two the actual process taking place is engine braking.

Longhorn said: Sudden acceleration/deceleration leads to excessive fuel consumption not to mention the increased wear and tear on your vehicle. No two ways about it. Ever wondered why you always get better FE on the highway than in the city. That's because we are able to maintain a constant speed for a longer period of time on the highway, which is just not possible in city traffic.

Di1in said: You have misunderstood what I said: When you simply engage a gear in a coasting car (accelerator pedal not depressed) the engine does not consume fuel (I meant "more fuel" as that is what we were talking about). The effect that you get here is engine braking.
What you have said is about accelerating a car - when the pedal is pressed - which obviously requires more fuel.
You get better FE while cruising on the highway not just because of the constant speed, but also because you are in a higher gear at a sweeter engine rpm with little swerving. The constant speed just helps the ecu to tune the fuel injection to a slightly leaner mix.

Summary:
I say that the car does not consume more fuel when it is coasting and deccelerating.
Longhorn says the car consumes more fuel whether it accelerates or deccelerates regardless of coasting.

Verdict: ??

[suhaas307]

As per my understanding, when one is in neutral, the cylinders are injected with a marginal quantity of fuel to keep the engine on the boil. But when in gear, if you are NOT accelerating, the injectors don't spit fuel into the cylinder and it's just the momentum that takes it forward. However, I'd recently learned that modern cars' ECUs let the engine stay at a particular speed, and in gear by injecting small-doses of fuel - thereby ensuring that the engine doesn't fall out of the rev-band for that particular gear (unless you apply the brakes)

Sutripa should probably be able to answer this best.

That said, It isn't advisable to leave the car in neutral in order to coast and come to a halt. The engine's revs go up marginally when you shift to neutral(?) and most importantly, you don't have complete control over your car. If you are required to perform an emergency maneuver like swerving (which itself is never recommended) or braking-hard and then moving forward, you won't be able to.

It's always recommended to keep the car in gear, irrespective of fuel-saving measures.

[the_maassk]

This is in gear. The vehicle decelerates until the point the ECU detects stalling where it sustains the engine to prevent stalling.

If practiced well, this does improve the FE. For instance, if you see traffic stopped fairly well in advance, just take your foot off the A pedal and let it decelerate.

Originally Posted by m_upreti

Is this in neutral or in gear.

In my Scorpio even I lift my foot off the A pedal, and the vehicle is in geat (say 1st) it continues moving without stalling which shows that the fuel is being fed to the engine ( I have however not tested the distance it would move in this condition, but it does manage to climb a 25 degree ramp without any issues).

[m_upreti]

Originally Posted by the_maassk

This is in gear. The vehicle decelerates until the point the ECU detects stalling where it sustains the engine to prevent stalling.

If practiced well, this does improve the FE. For instance, if you see traffic stopped fairly well in advance, just take your foot off the A pedal and let it decelerate.

But not very practical in day to day scenario unless you are in an extremely slow moving traffic and want to rest your foot.