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Old 2nd July 2012, 09:32   #601
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Default Re: ARTICLE: How to get the maximum Fuel Efficiency

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Originally Posted by raycers_honda View Post
The assumptions are right.Also some times much before approaching a stop light i shift the car in neutral and let it roll upto the stop light.Dont know whether that helps in fuel efficiency in the long run.Not much use of brakes here but only a slight tap to reduce the speed gradually.
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Originally Posted by AutoIndian View Post
Please do not do this, "shift the car in neutral and let it roll upto the stop light". This makes the car to roll on free wheels, you don't get any assistance of engine braking & stopping the car in case of an emergency would be far more difficult. There is hardly any fuel saving if you coast your car on neutral till the traffic light rather than in higher gear. It is not at all worth taking the risk. When you are nearing the traffic light in higher gear (4th or 5th) just take your foot off the accelerator pedal & let the car coast on the higher gear, due to the inertia it can easily travel upto the signal, w/o you giving any accelerator input
Not only the safety factor. It is my belief that this actually burns more fuel instead. MPFI vehicles have a fuel cut off based on throttle operation. It means when the foot is off the throttle, the fuel supply is cut off from the engine, and the engine is run by the inertia of the wheels. It is something like a reverse process, where the movement of the wheels generates the force to keep the pistons moving and the engine running.

However, I do not vouch for the accuracy of the above mentioned facts. I had read them on some website, but do not remember where.

Considering that the scenario stated above is correct, by shifting into neutral and rolling to a stop will actually consume more fuel. This is because in neutral the engine is disconnected from the wheels, and thus the momentum of the wheels cannot work to keep the engine running. Thus, fuel supply to the engine must be given, only to keep the engine running, and not to move the car. The car moves on its own inertia, which is wasted since it is not being used to run the engine.

Same concept also applies to the scenario of driving downhill in neutral. Safety considerations apart, it means burning more fuel, as opposed to driving in gear, where as long as the car is rolling and there is no throttle input, fuel supply would be cut off.

I think this was also mentioned somewhere on the forum by another member. Will provide a link to that post if I can find it..

EDIT 1: In fact, this can very well be verified by simulating the situation. Try the following:
1. Stop on a slope, facing downhill. (The slope should be of decent gradient. Very gentle slope might not work).
2. Shift into first, and start accelerating. Slowly, but gradually.
3. When the speed reaches around 10-12 kmph (or whatever speed you generally shift into 2nd), leave the throttle, depress the clutch, shift into 2nd. Release the clutch, but do not accelerate. The car will continue to move forward. Also, you can see the RPMs increasing slowly, as the car rolls downhill without any throttle input.
4. When the engine reaches optimum RPM in 2nd, (by optimum RPM I mean whatever RPM that you generally upshift at), shift into 3rd, and continue without using the throttle. Again, the RPMs can be seen increasing.

Continuing this process, we can see that as the speed of the car increases, owing to downhill momentum, so does the engine RPM wrt to the current gear, without any throttle input whatsoever. This means that the increase in engine RPM is due to the rotation of the wheels, which drives the engine pistons. This is a reverse process. This means, that the engine is running without any fuel supply (or maybe minimum fuel supply).

Caution: While accelerating downhill, do not keep shifting up only to test this phenomenon. Increase your speed only till a comfortable limit, where you can drive at the required speed without needing to use the brakes to keep the speed in check. Safety first!!

Last edited by swarnava.m : 2nd July 2012 at 09:59.
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Old 2nd July 2012, 10:32   #602
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Default Re: ARTICLE: How to get the maximum Fuel Efficiency

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Originally Posted by swarnava.m View Post
However, I do not vouch for the accuracy of the above mentioned facts. I had read them on some website, but do not remember where.
You are right that coasting in gear does save fuel. But I doubt whether there is any fuel saving running thus before a signal. This is because the ECU cuts off the fuel supply only above a certain RPM. And though we get good control due to engine braking while downing the gear, it is difficult to stop the vehicle at the same time when the engine is running at high RPM, in traffic situations. The RPM tend to come down pretty fast, thereby moving away from the cut-off advantage.

More info on coasting in gear can be had at http://www.team-bhp.com/forum/techni...ml#post2400868 (Does coasting save fuel?) and the whole thread.
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Old 2nd July 2012, 10:37   #603
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Default Re: ARTICLE: How to get the maximum Fuel Efficiency

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Originally Posted by thoma View Post
You are right that coasting in gear does save fuel. But I doubt whether there is any fuel saving running thus before a signal. This is because the ECU cuts off the fuel supply only above a certain RPM. And though we get good control due to engine braking while downing the gear, it is difficult to stop the vehicle at the same time when the engine is running at high RPM, in traffic situations. The RPM tend to come down pretty fast, thereby moving away from the cut-off advantage.

More info on coasting in gear can be had at http://www.team-bhp.com/forum/techni...ml#post2400868 (Does coasting save fuel?) and the whole thread.
Are you sure that fuel supply is cut off only above a particular RPM? Why I ask this is because, if below a particular RPM, if fuel was being supplied, then without throttle input the car would knock.

Or am I missing something?
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Old 2nd July 2012, 10:52   #604
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Default Re: ARTICLE: How to get the maximum Fuel Efficiency

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Originally Posted by swarnava.m View Post
Are you sure that fuel supply is cut off only above a particular RPM? Why I ask this is because, if below a particular RPM, if fuel was being supplied, then without throttle input the car would knock.

Or am I missing something?
I guess so, if I remember correctly. You have to go through the link to get more info. When the RPM lowers below the point where the wheels are no longer turning the drive shaft, to avoid stalling, the ECU tries to pump more fuel.
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Old 2nd July 2012, 10:54   #605
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Default

Quote:
Originally Posted by swarnava.m View Post
Not only the safety factor. It is my belief that this actually burns more fuel instead. MPFI vehicles have a fuel cut off based on throttle operation. It means when the foot is off the throttle, the fuel supply is cut off from the engine, and the engine is run by the inertia of the wheels. It is something like a reverse process, where the movement of the wheels generates the force to keep the pistons moving and the engine running.

However, I do not vouch for the accuracy of the above mentioned facts. I had read them on some website, but do not remember where.

Considering that the scenario stated above is correct, by shifting into neutral and rolling to a stop will actually consume more fuel. This is because in neutral the engine is disconnected from the wheels, and thus the momentum of the wheels cannot work to keep the engine running. Thus, fuel supply to the engine must be given, only to keep the engine running, and not to move the car. The car moves on its own inertia, which is wasted since it is not being used to run the engine.

Same concept also applies to the scenario of driving downhill in neutral. Safety considerations apart, it means burning more fuel, as opposed to driving in gear, where as long as the car is rolling and there is no throttle input, fuel supply would be cut off.

I think this was also mentioned somewhere on the forum by another member. Will provide a link to that post if I can find it..

EDIT 1: In fact, this can very well be verified by simulating the situation. Try the following:
1. Stop on a slope, facing downhill. (The slope should be of decent gradient. Very gentle slope might not work).
2. Shift into first, and start accelerating. Slowly, but gradually.
3. When the speed reaches around 10-12 kmph (or whatever speed you generally shift into 2nd), leave the throttle, depress the clutch, shift into 2nd. Release the clutch, but do not accelerate. The car will continue to move forward. Also, you can see the RPMs increasing slowly, as the car rolls downhill without any throttle input.
4. When the engine reaches optimum RPM in 2nd, (by optimum RPM I mean whatever RPM that you generally upshift at), shift into 3rd, and continue without using the throttle. Again, the RPMs can be seen increasing.

Continuing this process, we can see that as the speed of the car increases, owing to downhill momentum, so does the engine RPM wrt to the current gear, without any throttle input whatsoever. This means that the increase in engine RPM is due to the rotation of the wheels, which drives the engine pistons. This is a reverse process. This means, that the engine is running without any fuel supply (or maybe minimum fuel supply).

Caution: While accelerating downhill, do not keep shifting up only to test this phenomenon. Increase your speed only till a comfortable limit, where you can drive at the required speed without needing to use the brakes to keep the speed in check. Safety first!!
Good explanation.
i believe porsche has developed a new transmission for the Boxter which has this feature "coasting".On one of the website it says, "Coasting is better for fuel consumption
because it enables the vehicle to harness its kinetic
energy and convert it into forward motion."
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Old 24th September 2012, 14:22   #606
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Default Mahindra Logan Diesel Low FE. Please Help.

Hello there,

We have a Logan DLE 1.5 DCi in the family. It used to return 20-27 kmpl on Diesel during its early ownership days. After 3rd service, the FE reduced and the vibrations of the engine increased suddenly. This was about 3 years back.

We tried all sorts of solutions to fix the vibrations and since then they have visibly reduced. But the FE remains abysmally low at about 9-10kmpl. Since the usage of the car has been city only, it barely runs ~700-800km / month. My brother, who usually drives the car has learnt to live with this low FE figure since he was not even calculating how much FE the car was returning. But recently, I happened to check the FE (after the Diesel price hike) and realized that it returned a partly 9.5kmpl.

There is no trouble with power delivery or acceleration. None of the parameters of ECU show any fault. The only *different* bit I could deduce was a whistling noise when the turbo spools up. But then this noise has been with us since day one when the car used to return 20-25+ kmpl.

My brother had posted the entire issue back in September 2010 here. Quoting the text here for reader convenience.

Quote:
Originally Posted by keanu_reeves@TBHP.com
My Logan 1.5 DLE has started Vibrating when it was 8 months old and it's NVH went higher by the day. I informed the Service center about it. But they where not able to find any fault.

As being from Nasik. I tapped some resources and Rang some telephones and caught hold of some Engineers from Mahindra. Was in the service center with them full day. They where Not able to test some Parameters. They Deduced that the ECU of my Logan is Faulty. The engineer told me that the ECU has lost some Settings it can neither be reset or reprogrammed or remapped as it is locked by Renault. It is a very costly affair to change the ECU.

Another Thing is We tested the car with another ECU from another car and the car stopped Vibrating and It's NVH came down to a very low level, It was sounding like a new car. The parameter which was not coming up on there computer showed up. The smell of the burnt fuel also changed it was not smelling of unburnt diesel. It took about 30 minutes to Do all the testing.

After that the ECU of my car was put back the NVH again went up the smell of the unburnt diesel came back. But the parameters which where not coming up Previously on the laptop came on.

NVH is high cos the Idling RPM for the car is around 950 and it should be around 810.

Now I am in a fix that the Vehicle is around 30 months old and very much out of warranty.

Hope some body can help me
Source: http://mahindralogan.forumotion.com/...w-fuel-economy

After we did all this, the SVC people checked if all cylinders were firing and they were. So they reset the ECU and the Harshness visibly reduced. But there was no positive effect on the FE. The FE hovers around 9.5-10kmpl in Nasik city, ~8kmpl in Pune city (By comparison I used to get 7.5-9 kmpl on my Civic AT in the very same Pune traffic). We have even tried asking on Romanian Dacia Logan forums but all they have to say is even with the ECU in limp mode, the car should return close to 16kmpl.

What could be the issue? Any pointers which could help? Please Help!!
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Old 24th September 2012, 14:37   #607
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Default Re: Mahindra Logan Diesel Low FE. Please Help.

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Originally Posted by antz.bin View Post
Hello there,

We have a Logan DLE 1.5 DCi in the family. It used to return 20-27 kmpl on Diesel during its early ownership days. After 3rd service, the FE reduced and the vibrations of the engine increased suddenly. This was about 3 years back.

We tried all sorts of solutions to fix the vibrations and since then they have visibly reduced. But the FE remains abysmally low at about 9-10kmpl. Since the usage of the car has been city only, it barely runs ~700-800km / month. My brother, who usually drives the car has learnt to live with this low FE figure since he was not even calculating how much FE the car was returning. But recently, I happened to check the FE (after the Diesel price hike) and realized that it returned a partly 9.5kmpl.

There is no trouble with power delivery or acceleration. None of the parameters of ECU show any fault. The only *different* bit I could deduce was a whistling noise when the turbo spools up. But then this noise has been with us since day one when the car used to return 20-25+ kmpl.

My brother had posted the entire issue back in September 2010 here. Quoting the text here for reader convenience.



Source: http://mahindralogan.forumotion.com/...w-fuel-economy

After we did all this, the SVC people checked if all cylinders were firing and they were. So they reset the ECU and the Harshness visibly reduced. But there was no positive effect on the FE. The FE hovers around 9.5-10kmpl in Nasik city, ~8kmpl in Pune city (By comparison I used to get 7.5-9 kmpl on my Civic AT in the very same Pune traffic). We have even tried asking on Romanian Dacia Logan forums but all they have to say is even with the ECU in limp mode, the car should return close to 16kmpl.

What could be the issue? Any pointers which could help? Please Help!!

Can you give some more details about your vehicle.
  1. The total running clocked.
  2. Any aproblems while starting when hot/cold.
  3. smoke ( colour and quantity)
  4. pick-up / acceleration.
  5. the most important how do you calcllate FE. Is it by tank full to tankfull ?
  6. can you give me the details of the error code you got when you hooked on the car on to a scanner
If the car gets into limp mode it will not accelerate beyond 1500 rpm and the light on the dash comes on constantly
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Old 24th September 2012, 14:59   #608
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Default Re: Mahindra Logan Diesel Low FE. Please Help.

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Originally Posted by CRDIsamir View Post
Can you give some more details about your vehicle.
  1. The total running clocked.
  2. Any aproblems while starting when hot/cold.
  3. smoke ( colour and quantity)
  4. pick-up / acceleration.
  5. the most important how do you calcllate FE. Is it by tank full to tankfull ?
  6. can you give me the details of the error code you got when you hooked on the car on to a scanner
If the car gets into limp mode it will not accelerate beyond 1500 rpm and the light on the dash comes on constantly
A1: Current odo reading is 47200km
A2: No starting problems. Starts in 1 crank always.
A3: Smoke is colorless while idling, mild black smoke under high acceleration.
A4: Normal as other Logans which return double FE.
A5: Tankfull method
A6: No error codes after resetting the ECU. Don't remember error codes prior to reseting. Reset was done in Sept. 2010. The car is not in Limp mode. I can rev all the way till 4-5k. Don't remember how much because I rarely take it over 3k.

Last edited by antz.bin : 24th September 2012 at 15:00.
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Old 24th September 2012, 15:19   #609
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Default Re: Mahindra Logan Diesel Low FE. Please Help.

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Originally Posted by antz.bin View Post
A1: Current odo reading is 47200km
Is the driving route the same as the days of higher FE? Reason I ask is, short commutes give poorer economy than longer drives (where the engine has reached its operating temperature).
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Old 24th September 2012, 15:28   #610
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Default Re: Mahindra Logan Diesel Low FE. Please Help.

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Originally Posted by GTO View Post
Is the driving route the same as the days of higher FE? Reason I ask is, short commutes give poorer economy than longer drives (where the engine has reached its operating temperature).
Yes. All quoted FE are inside Nasik city limits which has much much lower traffic than Pune / Mumbai. The commute routes and timings are exactly the same as before. The FE reduction had happened abruptly after 3rd service. Something that SCV people haven't been able to fix as yet.

Everyone/Anyone I talk to in M&M / SVC says such low FE is totally unacceptable. The Service Head at Jitendra Auto Nasik himself owns a Logan and his car returns between 19-21kmpl (as per the MID). We have spent and wasted a lot of time in the SVC for an issue we haven't been able to fix.

Last edited by antz.bin : 24th September 2012 at 15:35.
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Old 24th September 2012, 16:52   #611
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Default Re: ARTICLE: How to get the maximum Fuel Efficiency

Just read the write up on the Mahindra Logan forum. You have mentioned that the ECU was changed with that of other car. Was this done in front of you or your brother ?. I am asking this because changing the ECU is not done done in 30 minutes as mentioned on the forum. To change the ECU you have to change the ingnition switch as well which has the immobiliser which is matched with the ECU. Also there is one more ECU in the passenger compartment which is also to be changed.

Try cleaning the Air sensor which is located on the Air Cleaner with WD 40. Also clean the EGR valve. If other parameters like acceleration, starting and smoke are ok then there should not be any issue with the any systems. Look out for any leagkages in the plumbings of the Turbo and intercooler as you have mentioned the whistling sound when the Turbo builds up the boost pressure.

keep me updated.
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Old 24th September 2012, 17:07   #612
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Default Re: ARTICLE: How to get the maximum Fuel Efficiency

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Originally Posted by CRDIsamir View Post
keep me updated.
The other car had come for an accident repair and the ECU of that car was just hanged on to mine for checking only and none of the cars where moved at that time. All this happened in my presence the SVC people and that engineer again took the readings and plugged mine back.
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Old 30th September 2012, 02:13   #613
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Default Re: ARTICLE: How to get the maximum Fuel Efficiency

This is probably the weirdest way to save fuel. But apparently it seems you can save fuel if you make only left turns ( for right hand driving ). Recently saw this in an episode from Discovery channel's MythBusters. - http://planetgreen.discovery.com/tec...-save-gas.html
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Old 4th October 2012, 21:45   #614
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Default Fuel Consumption on Ford Fiesta(1.4P) shot up post AC Repair

Hello All,

I recently had a problem with my ford fiesta(1.4-petrol) AC Compressor. The gas was leaking off and i got it checked with the A.S.S and they suggested to replace the same at est cost of 38k. Since it was quite some money i got it checked with Carz and they agreed to repair the compressor which they did at 6k and AC works perfect now..But i see two major issues post this work

1) The radiator fan noise has gone up considerably post the repair work & Switches on very frequently and sometime don't get tripped off automatically--I did get this checked again with the A.S.S and they changed sensor and said every thing is fine-but i still observe the fan running at higher speed most of the times. May be i haven't observed this before.

2) The fuel consumption have shot up incredibly. I am not sure if its any-way linked to this, but wanted to check.

What could be the possible reasons behind this.Are these problems linked with each other?

I am yet to take the car to A.S.S and planning to take it next week.Hopefully they don't give me a shock!!
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Old 5th October 2012, 04:50   #615
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Default Re: Fuel Consumption on Ford Fiesta(1.4P) shot up post AC Repair

Fuel consumption can go up by 10% when the A/C is operating. Check your coolant levels & top up.

The A/C repair guys must have put in extra A/C gas to satisfy the customer. This causes more load on the engine & makes it work harder than usual. Though you get good cooling (better than before) the down-side is much increased load on the engine.
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