Does a car consume fuel under engine braking?

[DivideBYZero]

Originally posted by: jagec

Originally posted by: d0ofy
I engine brake pretty often. When I press the clutch when engine braking the RPMs shoot up 1K+. If the fuel is absolutely cut off when engine braking, what causes that sudden increase in RPMs?

I've never seen a car that behaves as you describe. Are you sure your foot is 100% off the gas, and nothing in your transmission is slipping? When I push the clutch while engine braking, the engine just drops to idle. In every vehicle I've driven. Which is quite a few.

It drops to idle because of all the fuel that has been going into the bang-holes and not being used. Engine braking is bad, because you put wear on the muffler bearings.

 

[d0ofy]

Originally posted by: jagec

Originally posted by: d0ofy
I engine brake pretty often. When I press the clutch when engine braking the RPMs shoot up 1K+. If the fuel is absolutely cut off when engine braking, what causes that sudden increase in RPMs?

I've never seen a car that behaves as you describe. Are you sure your foot is 100% off the gas, and nothing in your transmission is slipping? When I push the clutch while engine braking, the engine just drops to idle. In every vehicle I've driven. Which is quite a few.

It's a fairly new Mazda3 if anyone has one and wants to try it. To clarify, the engine shoots up for about a second then drops to idle.

 

[RichUK]

Originally posted by: d0ofy

Originally posted by: RichUK

Originally posted by: d0ofy
I engine brake pretty often. When I press the clutch when engine braking the RPMs shoot up 1K+. If the fuel is absolutely cut off when engine braking, what causes that sudden increase in RPMs?

Inertia

EDIT: Also i am pretty sure you cannot engine brake under idle anyway. Not that i have tried.

I have actually done that a few times. Idle on my car is around 750 and I've dipped below 500 before while braking. The moment I pressed the clutch the engine corrected up to above idle then rested at idle.

Thats weird because i can understand the dip in revs when you slip the clutch. Or have bad changes. But not under engine braking. Then again i rarely ever engine brake.

 

[spidey07]

Originally posted by: d0ofy
It's a fairly new Mazda3 if anyone has one and wants to try it. To clarify, the engine shoots up for about a second then drops to idle.

Let me guess?

Drive by wire?

 

[Tom]

Originally posted by: randay

Originally posted by: Tom
Yes, I know. My point is, assuming some cars use something like this, then it isn't true that all cars with EFI cut off fuel delivery entirely during engine braking, which a great deal of posts in this thread insists is the case.

I can't believe that after all we've been through in this thread, people are still spewing random facts with nothing to back it up. unbelievable!

LOL, you don't consider a US Patent as good a source as ATOT ?

 

[RichUK]

Originally posted by: DivideBYZero

Originally posted by: jagec

Originally posted by: d0ofy
I engine brake pretty often. When I press the clutch when engine braking the RPMs shoot up 1K+. If the fuel is absolutely cut off when engine braking, what causes that sudden increase in RPMs?

I've never seen a car that behaves as you describe. Are you sure your foot is 100% off the gas, and nothing in your transmission is slipping? When I push the clutch while engine braking, the engine just drops to idle. In every vehicle I've driven. Which is quite a few.

It drops to idle because of all the fuel that has been going into the bang-holes and not being used. Engine braking is bad, because you put wear on the muffler bearings.

:laugh:

Too funny

 

[d0ofy]

Originally posted by: spidey07

Originally posted by: d0ofy
It's a fairly new Mazda3 if anyone has one and wants to try it. To clarify, the engine shoots up for about a second then drops to idle.

Let me guess?

Drive by wire?

That it is... does that explain it?

 

[Tom]

Originally posted by: Zenmervolt

Originally posted by: Tom
Yes, I know. My point is, assuming some cars use something like this, then it isn't true that all cars with EFI cut off fuel delivery entirely during engine braking, which a great deal of posts in this thread insists is the case.

Unless you're buying cars made in a third-world country, all modern FI vehicles have a fuel cut-off under engine braking. It's a "free" way for the auto maker to increase fuel mileage for a vehicle.

There are differing methods for resuming fuel injection when the threshold RPM has been breached, but any modern FI car will cut off fuel under deceleration.

The pattent only addresses the brief (less than one second) transition period from normal fuel flow to fuel cut-off. It actually proves that any car using your patent does have a 100% cut-off mode since the pattent covers only the transition to and from complete fuel cut-off.

ZV

Your own reply corroborates my statement. And disproves the opposite claim. Even if the duration is brief, which is information you supply, not me, then the fact is a car with such a system would consume fuel, perhaps a very small amount, during engine braking.

And before you interject that the amount is trivial, by the same token this entire discussion is about a trivial difference in fuel consumption, except for those lucky few who only ever drive downhill.

 

[spidey07]

Originally posted by: d0ofy

Originally posted by: spidey07

Originally posted by: d0ofy
It's a fairly new Mazda3 if anyone has one and wants to try it. To clarify, the engine shoots up for about a second then drops to idle.

Let me guess?

Drive by wire?

That it is... does that explain it?

I'm not a super knowledgable car guy, but my acura does something similar, it will even rev match your up shifts for you. For example when upshifting the ECU will hold the throttle open even if I am not pressing throttle to maintain the correct RPM.

My guess is the ecu is opening the throttle a little bit. Since you have a manual it might think you are trying to shift and it is getting the RPMs up to where the need to be. Again, my TL does this.

 

[Raduque]

Originally posted by: Regs

Originally posted by: jagec

Originally posted by: Regs

Originally posted by: KLin
As long as the engine is running, it's consuming fuel.

Fact. If your car was ever cut off from fuel it would stall. Idle is on most cars at 1200-1600 RPM.

Those are two of the worst "facts" I've ever heard:laugh:

So, if I grab a car out of the junkyard that has a completely dry fuel tank, push it down a hill in second, and pop the clutch, the pistons will not move one iota and the engine will promptly leap out of the hood in a huge oily mess? Funny, I've RUN out of a gas while driving, and the car just slowly coasts to a stop, preserving power steering and brakes as long as I keep it in gear. If I put gas in it, I can restart the engine by rolling it down a hill and popping the clutch.

Also, most cars idle below 1000RPM.

Ok - 600 rpm - 1,000 rpm for a passenger car. I believe my Honda runs a little over 1k which is great because I can run my AC without stalling. 600-1000 is enough to run the water pump , power steering and alternator. On a side note, running the car out of fuel could cause vapor lock, but you're right, it wont pop out of the hood in a oily mess. lol. But the question was if the car would consume gas rolling down a hill. At least I thought it was. Maybe I didn't get it.

I have absolutely no input on the overall topic (I coast to a stop on a flat area but run through the gears with the clutch pressed the whole time), but I just have to say: My Accord idles at 850, but my Oldsmobile when I had it idled at 500rpm. I had to use a vacuum canister to run my power brakes


Actually, now that I think about it, I'm pretty sure my accord has a complete cutoff between 1k and like 3k under engine braking - it's a pretty perceptible jerk when you go back on-power between that range.

 

[randay]

Originally posted by: Tom

Originally posted by: Zenmervolt

Originally posted by: Tom
Yes, I know. My point is, assuming some cars use something like this, then it isn't true that all cars with EFI cut off fuel delivery entirely during engine braking, which a great deal of posts in this thread insists is the case.

Unless you're buying cars made in a third-world country, all modern FI vehicles have a fuel cut-off under engine braking. It's a "free" way for the auto maker to increase fuel mileage for a vehicle.

There are differing methods for resuming fuel injection when the threshold RPM has been breached, but any modern FI car will cut off fuel under deceleration.

The pattent only addresses the brief (less than one second) transition period from normal fuel flow to fuel cut-off. It actually proves that any car using your patent does have a 100% cut-off mode since the pattent covers only the transition to and from complete fuel cut-off.

ZV

Your own reply corroborates my statement. And disproves the opposite claim. Even if the duration is brief, which is information you supply, not me, then the fact is a car with such a system would consume fuel, perhaps a very small amount, during engine braking.

And before you interject that the amount is trivial, by the same token this entire discussion is about a trivial difference in fuel consumption, except for those lucky few who only ever drive downhill.

One can also be just as anal and argue that at the moment in question, the car is not engine braking but transitioning from engine braking to Idling or accelerating.

Also you don't have to be lucky "to ever drive downhill" the world isn't flat you know, besides, engine braking can occur on flat ground, even uphill.

 

[Tom]

Originally posted by: randay

Originally posted by: Tom

Originally posted by: Zenmervolt

Originally posted by: Tom
Yes, I know. My point is, assuming some cars use something like this, then it isn't true that all cars with EFI cut off fuel delivery entirely during engine braking, which a great deal of posts in this thread insists is the case.

Unless you're buying cars made in a third-world country, all modern FI vehicles have a fuel cut-off under engine braking. It's a "free" way for the auto maker to increase fuel mileage for a vehicle.

There are differing methods for resuming fuel injection when the threshold RPM has been breached, but any modern FI car will cut off fuel under deceleration.

The pattent only addresses the brief (less than one second) transition period from normal fuel flow to fuel cut-off. It actually proves that any car using your patent does have a 100% cut-off mode since the pattent covers only the transition to and from complete fuel cut-off.

ZV

Your own reply corroborates my statement. And disproves the opposite claim. Even if the duration is brief, which is information you supply, not me, then the fact is a car with such a system would consume fuel, perhaps a very small amount, during engine braking.

And before you interject that the amount is trivial, by the same token this entire discussion is about a trivial difference in fuel consumption, except for those lucky few who only ever drive downhill.

One can also be just as anal and argue that at the moment in question, the car is not engine braking but transitioning from engine braking to Idling or accelerating.

Also you don't have to be lucky "to ever drive downhill" the world isn't flat you know, besides, engine braking can occur on flat ground, even uphill.

When some one points out a discrepancy in a group's accepted belief, it is common to ridicule the deliverer of the bad news, rather than accept that one's belief was erroneous.

Hence, your use of the word, anal.

1. Engine braking occurs because the engine's power output is lowered causing the engine 's rpm to drop which in turn slows the vehicle. That process does not require the fuel to be completely shut off. Shutting the fuel off to some of the cylinders would cause engine braking, during which time the remaining cylinders would still be consuming fuel.

2. I didn't say engine braking requires going downhill.

 

[Vic]

This thread makes Baby Jesus cry.

 

[randay]

Originally posted by: Tom

Originally posted by: randay

Originally posted by: Tom

Originally posted by: Zenmervolt

Originally posted by: Tom
Yes, I know. My point is, assuming some cars use something like this, then it isn't true that all cars with EFI cut off fuel delivery entirely during engine braking, which a great deal of posts in this thread insists is the case.

Unless you're buying cars made in a third-world country, all modern FI vehicles have a fuel cut-off under engine braking. It's a "free" way for the auto maker to increase fuel mileage for a vehicle.

There are differing methods for resuming fuel injection when the threshold RPM has been breached, but any modern FI car will cut off fuel under deceleration.

The pattent only addresses the brief (less than one second) transition period from normal fuel flow to fuel cut-off. It actually proves that any car using your patent does have a 100% cut-off mode since the pattent covers only the transition to and from complete fuel cut-off.

ZV

Your own reply corroborates my statement. And disproves the opposite claim. Even if the duration is brief, which is information you supply, not me, then the fact is a car with such a system would consume fuel, perhaps a very small amount, during engine braking.

And before you interject that the amount is trivial, by the same token this entire discussion is about a trivial difference in fuel consumption, except for those lucky few who only ever drive downhill.

One can also be just as anal and argue that at the moment in question, the car is not engine braking but transitioning from engine braking to Idling or accelerating.

Also you don't have to be lucky "to ever drive downhill" the world isn't flat you know, besides, engine braking can occur on flat ground, even uphill.

When some one points out a discrepancy in a group's accepted belief, it is common to ridicule the deliverer of the bad news, rather than accept that one's belief was erroneous.

Hence, your use of the word, anal.

1. Engine braking occurs because the engine's power output is lowered causing the engine 's rpm to drop which in turn slows the vehicle. That process does not require the fuel to be completely shut off. Shutting the fuel off to some of the cylinders would cause engine braking, during which time the remaining cylinders would still be consuming fuel.

2. I didn't say engine braking requires going downhill.

And could you link me to the US Patent that you are referring to for point 1 and 2? I seem to have missed the post backing up your "facts".

 

[DivideBYZero]

Originally posted by: Vic
This thread makes Baby Jesus cry.

Is baby Jesus still rolling? Then he's using fuel.

 

[jagec]

Originally posted by: Tom
Your own reply corroborates my statement. And disproves the opposite claim. Even if the duration is brief, which is information you supply, not me, then the fact is a car with such a system would consume fuel, perhaps a very small amount, during engine braking.

And before you interject that the amount is trivial, by the same token this entire discussion is about a trivial difference in fuel consumption, except for those lucky few who only ever drive downhill.

Again proving that you didn't read the patent. It consumes fuel right BEFORE engine braking, and right AFTER, but none, zero, zilch, DURING any engine braking of nontrivial duration.

Weren't you one of the people arguing that the plane wouldn't take off, too? Are you just a physics troll?

 

[randay]

Originally posted by: DivideBYZero

Originally posted by: Vic
This thread makes Baby Jesus cry.

Is baby Jesus still rolling? Then he's using fuel.

No he is not rolling, he is in neutral. He is not using any fuel. If he wasnt using any fuel you would have to keep starting your baby jesus up again from the locked and upright position.

 

[DivideBYZero]

Originally posted by: Tom

Originally posted by: randay

Originally posted by: Tom

Originally posted by: Zenmervolt

Originally posted by: Tom
Yes, I know. My point is, assuming some cars use something like this, then it isn't true that all cars with EFI cut off fuel delivery entirely during engine braking, which a great deal of posts in this thread insists is the case.

Unless you're buying cars made in a third-world country, all modern FI vehicles have a fuel cut-off under engine braking. It's a "free" way for the auto maker to increase fuel mileage for a vehicle.

There are differing methods for resuming fuel injection when the threshold RPM has been breached, but any modern FI car will cut off fuel under deceleration.

The pattent only addresses the brief (less than one second) transition period from normal fuel flow to fuel cut-off. It actually proves that any car using your patent does have a 100% cut-off mode since the pattent covers only the transition to and from complete fuel cut-off.

ZV

Your own reply corroborates my statement. And disproves the opposite claim. Even if the duration is brief, which is information you supply, not me, then the fact is a car with such a system would consume fuel, perhaps a very small amount, during engine braking.

And before you interject that the amount is trivial, by the same token this entire discussion is about a trivial difference in fuel consumption, except for those lucky few who only ever drive downhill.

One can also be just as anal and argue that at the moment in question, the car is not engine braking but transitioning from engine braking to Idling or accelerating.

Also you don't have to be lucky "to ever drive downhill" the world isn't flat you know, besides, engine braking can occur on flat ground, even uphill.

When some one points out a discrepancy in a group's accepted belief, it is common to ridicule the deliverer of the bad news, rather than accept that one's belief was erroneous.

Hence, your use of the word, anal.

1. Engine braking occurs because the engine's power output is lowered causing the engine 's rpm to drop which in turn slows the vehicle. That process does not require the fuel to be completely shut off. Shutting the fuel off to some of the cylinders would cause engine braking, during which time the remaining cylinders would still be consuming fuel.

2. I didn't say engine braking requires going downhill.

1: Ahah!! YES!!! Proof that a car is STILL USING FUEL WHEN MOVING!!!

Never mind the firing sequence. Never mind the injector pulse bandwidth. THE CAR IS STILL FLOODING THE BOOM-PIPES!

All of you are owned and are wasting teh dollaRz. Yo ushould put it in NUTRAL and COAST all you can for MACSIMEM fuel shavings!!!

lol!

 

[Vic]

Originally posted by: DivideBYZero

Originally posted by: Vic
This thread makes Baby Jesus cry.

Is baby Jesus still rolling? Then he's using fuel.

:laugh:

 

[Nyati13]

Originally posted by: spidey07

Originally posted by: d0ofy

Originally posted by: spidey07

Originally posted by: d0ofy
It's a fairly new Mazda3 if anyone has one and wants to try it. To clarify, the engine shoots up for about a second then drops to idle.

Let me guess?

Drive by wire?

That it is... does that explain it?

I'm not a super knowledgable car guy, but my acura does something similar, it will even rev match your up shifts for you. For example when upshifting the ECU will hold the throttle open even if I am not pressing throttle to maintain the correct RPM.

My guess is the ecu is opening the throttle a little bit. Since you have a manual it might think you are trying to shift and it is getting the RPMs up to where the need to be. Again, my TL does this.

My Subaru has throttle-by-wire also and does the auto rev match for upshifts. When I clutch in on an upshift the RPMS will drop really quickly, and then 'bounce' back up to the proper RPM for the next gear at whatever speed I'm going. I haven't seen it 'bounce' the revs up, but the Mazda might also be trying to auto-rev match for downshifts, which the Subaru doesn't do ( I don't think it does, but it's new, and I haven't driven that hard yet.)

 

[dave518]

I know you all hate what I said earlier but can someone tell me what keeps the cylinders moving if you are in neutral and there is no gas being combusted?

 

[randay]

Originally posted by: dave518
I know you all hate what I said earlier but can someone tell me what keeps the cylinders moving if you are in neutral and there is no gas being combusted?

Nothing would keep the cylinders moving, the engine would stop. But I have a feeling you are not understanding what we are talking about. When engine braking you will be in gear, not neutral. The transmission will be turning over the engine in this case, while no combustion occurs. If you put the car into neutral while coasting the ECU kicks the fuel injectors into gear and gives enough gas to keep the engine at idle so that the engine doesn't stop.

 

[91TTZ]

Originally posted by: dave518
I know you all hate what I said earlier but can someone tell me what keeps the cylinders moving if you are in neutral and there is no gas being combusted?

We're talking about engine braking. Your car is not in neutral when engine braking.

 

[spidey07]

Originally posted by: randay

Originally posted by: dave518
I know you all hate what I said earlier but can someone tell me what keeps the cylinders moving if you are in neutral and there is no gas being combusted?

Nothing would keep the cylinders moving, the engine would stop. But I have a feeling you are not understanding what we are talking about. When engine braking you will be in gear, not neutral. The transmission will be turning over the engine in this case, while no combustion occurs. If you put the car into neutral while coasting the ECU kicks the fuel injectors into gear and gives enough gas to keep the engine at idle so that the engine doesn't stop.

To make it more clear...

Car and wheels are turning, wheels turn drive shaft, since we're in gear the drive shaft is turning the transmission, the transmission is turning the flywheel/crankshaft (we're in gear, effectively locking the motor and the wheels), of course that is moving the pistions up and down. Ever pull the cord on a lawn mower? Feel that resistance? That's the compression of the motor/piston, this takes work. With engine breaking that work of turning the crankshaft carries a signficant amount of resistance (you can't just turn the crank without being met with serious resistance, you're trying to compress air to 8-10 times it's normal density, that's hard, that's serious work). To put it briefely, grab the crankshaft of a motor and try to turn it one full rotation by hand, that should give you and idea.

I'm trying to really simplify it here so all the experts can give me a little bit of rope.

-edit-
randy, I'm just reinforcing your point.

 

[dug777]

Originally posted by: dave518
I know you all hate what I said earlier but can someone tell me what keeps the cylinders moving if you are in neutral and there is no gas being combusted?

:laugh:

You aren't for real are you? :laugh: