Does going down through the gears use fuel?

Do you use your gears to slow or coast up to a juncton?

  • Total voters
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Many Sat navs and smarphones have Apps for fuel economy.
Hard acceleration is what kills fuel economy followed by under inflated tyres.
Maybe the instructor meant to coast up to the lights in the hope they would go green so that you don't need to bring the vehicle to a halt. I have heard of that before for heavy goods lorries especially due to all the energy you burn getting them off the line. :dontknow:
 
[quote author=KENC link=topic=32327.msg371043#msg371043 date=1322250978]
If we forget the serious issue about safety and just think on the fuel consumption, When you down shift through the gears, think what position is your Throttle in??? answer is closed as in the same as tickover.. I would take a guess at having a car/ van lorry etc etc struggling in a gear would be a lot more fuel heavy than down shifting and having the Throttle shut off and engine braking the car
[/quote]

surely knocking it into neutral is the most flue efficient way, not safe but use the least fuel...once the engine is in gear it's doing work
 
[quote author=Dagnut link=topic=32327.msg371095#msg371095 date=1322308813]
[quote author=KENC link=topic=32327.msg371043#msg371043 date=1322250978]
If we forget the serious issue about safety and just think on the fuel consumption, When you down shift through the gears, think what position is your Throttle in??? answer is closed as in the same as tickover.. I would take a guess at having a car/ van lorry etc etc struggling in a gear would be a lot more fuel heavy than down shifting and having the Throttle shut off and engine braking the car
[/quote]

surely knocking it into neutral is the most flue efficient way, not safe but use the least fuel...once the engine is in gear it's doing work
[/quote]

If you are down shifting correctly you are using the engine to brake, its your momentum thats powering your engine not the opposite way around.. so that should mean minimum fuel use.
If you drive any car that has a fuel consumption computer they might not be an exact idea but if you take your foot off throttle going down a hill and let the gearing hold the cars speed and rev.. your computer should read 0 fuel consumption.
All big heavy goods vehicles us an Exhaust brake, which goes hand in hands with down shifting to optimise your slowing down capabilities without burning pads, disk, drums off them.
Ive driven both the 25 and 40 tonne dump trucks and on big road building jobs when you know how to drive the thing correctly the brakesare used very little, only to come to a dead hault, these are all automatic/semi auto so when you let foot off, exhaust brake comes on and it down gears itself , everytime it downs a gear you you have an increased exhaust brake effort.
All this is to minimise wear on wearing parts i.e the brake set up.

As much as i think the show is crap, if you look at ice road truckers you will see from time to time that the safest way and only way really on a steep decent is to pick your low gear that can hold you back going down the hill, if not you will burn off the brakes and worse again is half way down panic, and try to select a lower gear, clutch in and gearings is free from engine to pick up speed and you probably wont be able to re select a lower gear and be lucky to get back in gear at all.

For a while there was loads of Dumper trucks accidents, a lot of these were down to guys knocking them into neutral going down hill to get more speed, prtoblem was when they did this they forgot to keep revs up, so when they went to go steer the thing the steering was next to zero and sometimes konked the engine out on tick over..
So i wouldnt like to have to steer in an emergency when having the van struggling in 4th like this guy has advised
 
If I put it into neutral and let it coast and break at final stop (only if needed and not green again) i notice rev counter goes to idle speed of ~500RPM.

If I am downshifting then I am keeping the revs around 2000RPM by using the gears.

Surely the second method is using 4 times as much fuel? It all boils down to - is the Subaru ECU intelligent enough to not inject fuel if it detects deceleration is occuring? I mean if it HAS to do a single injection at every revolution then 2000RPM is definitely using more fuel than 500RPM. And anyway it definitely SOUNDS like it is doing this - i mean your engine doesn't go silent as you slow down does it? You still hear the bangs of detonation...
 
[quote author=geogan link=topic=32327.msg371377#msg371377 date=1322578900]
If I put it into neutral and let it coast and break at final stop (only if needed and not green again) i notice rev counter goes to idle speed of ~500RPM.

If I am downshifting then I am keeping the revs around 2000RPM by using the gears.

Surely the second method is using 4 times as much fuel? It all boils down to - is the Subaru ECU intelligent enough to not inject fuel if it detects deceleration is occuring? I mean if it HAS to do a single injection at every revolution then 2000RPM is definitely using more fuel than 500RPM. And anyway it definitely SOUNDS like it is doing this - i mean your engine doesn't go silent as you slow down does it? You still hear the bangs of detonation...


[/quote]
.
That was my theory also, once the engine is turning over rpm it is burning fuel no? It evens burns fuel on tick over..

.I'm not arguing the safety aspects
 
Lads cars dont inject on over run if they did they would sound like antilag while driving ,and would be very hard to stop at a junction as the engine would try to rev once the idle. Valve opens that is why the injecters are switched off at closed throttle until the engine is back to idle
 
[quote author=WAGON DEC link=topic=32327.msg371380#msg371380 date=1322582965]
Lads cars dont inject on over run if they did they would sound like antilag while driving ,and would be very hard to stop at a junction as the engine would try to rev once the idle. Valve opens that is why the injecters are switched off at closed throttle until the engine is back to idle
[/quote]

Sorry don't understand much of what you said there... :ponder:

What's "over run"?

"injectors are switched off at closed throttle"? - what does this mean? - sounds like you are saying if your foot is off the accelerator then fuel injection is turned off??? So what's keeping engine going then?
 
[quote author=WAGON DEC link=topic=32327.msg371380#msg371380 date=1322582965]
Lads cars dont inject on over run if they did they would sound like antilag while driving ,and would be very hard to stop at a junction as the engine would try to rev once the idle. Valve opens that is why the injecters are switched off at closed throttle until the engine is back to idle
[/quote]

How does the engine run on idle then?
 
[quote author=Dagnut link=topic=32327.msg371395#msg371395 date=1322588198]
[quote author=WAGON DEC link=topic=32327.msg371380#msg371380 date=1322582965]
Lads cars dont inject on over run if they did they would sound like antilag while driving ,and would be very hard to stop at a junction as the engine would try to rev once the idle. Valve opens that is why the injecters are switched off at closed throttle until the engine is back to idle
[/quote]

How does the engine run on idle then?
[/quote]


the engine will idle because when the ecu detects the idling rpm it opens the idle speed valve this in turn allows air to flow into the manifold, by air flowing into the manifold the air flow meter detects flow and measures the correct amount of fuel to allow the engine to idle.it is a very complicated system and hard to explain most ecu,s will make on average thousands of calculations per second so it can do things like that because its workin in miliseconds and will have the decision made and you wont even notice it
 
[quote author=WAGON DEC link=topic=32327.msg371450#msg371450 date=1322611342]
[quote author=Dagnut link=topic=32327.msg371395#msg371395 date=1322588198]
[quote author=WAGON DEC link=topic=32327.msg371380#msg371380 date=1322582965]
Lads cars dont inject on over run if they did they would sound like antilag while driving ,and would be very hard to stop at a junction as the engine would try to rev once the idle. Valve opens that is why the injecters are switched off at closed throttle until the engine is back to idle
[/quote]



How does the engine run on idle then?
[/quote]


the engine will idle because when the ecu detects the idling rpm it opens the idle speed valve this in turn allows air to flow into the manifold, by air flowing into the manifold the air flow meter detects flow and measures the correct amount of fuel to allow the engine to idle.it is a very complicated system and hard to explain most ecu,s will make on average thousands of calculations per second so it can do things like that because its workin in miliseconds and will have the decision made and you wont even notice it
[/quote]

But it's still using fuel right? so if it's at 2000rpm it will use more fuel than 1000rpm?
 
Best way to save fuel is to turn off at traffic lights, i tried it for a tank full one week as i have push button start/stop.

usually depending what humour im in average anywhere from 12.6 to 14.6l/100kms.

when i shut engine off at the lights i was 10.2l/100kms, drove me nuts after a while :wall:
 
Just out of curiosity, how does stopping\starting work with the radio, lights etc?
What I mean is, if I switched off the car and then switched on again, the radio would die and take 3 or 4 seconds to come back (which is most annoying when you're listening to something), and the lights would dimly flash until the engine came alive again (which would end up blowing the bulbs eventually).

Do cars with stop\start technology have a second battery to keep things going and therefore the above wouldn't happen??
 
But it's still using fuel right? so if it's at 2000rpm it will use more fuel than 1000rpm?
[/quote]

no its only using fuel when it reaches idle speed or if you get back on the throttle .any rpm above idle speed the idle speed valve will be closed so if you are off throttle slowing down or say down hill off throttle and the car engine is at lets say 1500 rpm your throttle plate is closed ,your idle speed valve is closed therefore the engine is in vacuum fuel can not burn with out air so the strategy of the ecu is to switch off the earth pulse to the injectors but once either you press the throttle or the engine slows to idle rpm then the injectors reactivate and the car stays running all this is done in miliseconds and undetectable to the driver
 
[quote author=WAGON DEC link=topic=32327.msg371539#msg371539 date=1322692730]

But it's still using fuel right? so if it's at 2000rpm it will use more fuel than 1000rpm?
[/quote]

no its only using fuel when it reaches idle speed or if you get back on the throttle .any rpm above idle speed the idle speed valve will be closed so if you are off throttle slowing down or say down hill off throttle and the car engine is at lets say 1500 rpm your throttle plate is closed ,your idle speed valve is closed therefore the engine is in vacuum fuel can not burn with out air so the strategy of the ecu is to switch off the earth pulse to the injectors but once either you press the throttle or the engine slows to idle rpm then the injectors reactivate and the car stays running all this is done in miliseconds and undetectable to the driver
[/quote]

so what would happen if you cut the fuel? say switched of the fuel pump? I don't understand how you can say it uses fuel on idle but not as you are gearing down
 
I think its because if you in neutral and let the car idle, then it has to use fuel to keep the engine running.

But if you are slowing down, in gear, then the engine is kept turning over by the cars momentum turning the wheel, gearbox & engine in turn so it doens't need to inject fuel to keep the engine running.
 
[quote author=Sweetcakes link=topic=32327.msg371564#msg371564 date=1322699137]
I think its because if you in neutral and let the car idle, then it has to use fuel to keep the engine running.

But if you are slowing down, in gear, then the engine is kept turning over by the cars momentum turning the wheel, gearbox & engine in turn so it doens't need to inject fuel to keep the engine running.
[/quote]

But why then do we still HEAR the sound of combustion while slowing down in gear? As I said previously it doesn't go silent does it... If the wheels/gears are keeping the engine running in deceleration and ECU stops the fuel injection then should be no sparks, no bangs and it should run without sound... The fact that I can hear the engine means it is using fuel :ponder:
 
[quote author=Sweetcakes link=topic=32327.msg371564#msg371564 date=1322699137]
I think its because if you in neutral and let the car idle, then it has to use fuel to keep the engine running.

But if you are slowing down, in gear, then the engine is kept turning over by the cars momentum turning the wheel, gearbox & engine in turn so it doens't need to inject fuel to keep the engine running.
[/quote]

So that should mean if you are in gear and rolling you could switch the ignition off and coast to rest? I'm not sure ...you cut fuel the engine stops.
 
[quote author=geogan link=topic=32327.msg371377#msg371377 date=1322578900]
If I put it into neutral and let it coast and break at final stop (only if needed and not green again) i notice rev counter goes to idle speed of ~500RPM.

If I am downshifting then I am keeping the revs around 2000RPM by using the gears.

Surely the second method is using 4 times as much fuel? It all boils down to - is the Subaru ECU intelligent enough to not inject fuel if it detects deceleration is occuring? I mean if it HAS to do a single injection at every revolution then 2000RPM is definitely using more fuel than 500RPM. And anyway it definitely SOUNDS like it is doing this - i mean your engine doesn't go silent as you slow down does it? You still hear the bangs of detonation...


[/quote]

Hi,

To answer the origional question, Kenc has done it above, when your off throttle rolling up to a junction/down hill and using the natural braking effort of the engine to slow you down, you are using zero fuel.

Question answered.

Rgds

Paddy
 
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