Does engine braking consume gas? [Archive] - Beyond.ca - Car Forums

syritis

10-20-2009, 06:07 PM

unless your braking at the last possible second before corners and would like to be in the correct gear for exiting in efforts to reduce your lap times, i can't think of any reason why you would want to wear out your expensive clutch before your inexpensive brake pads.

engine braking is also good for you motor occasionally. apparently the higher vacuum can break up some carbon build ups in the intake.

Sentry

10-20-2009, 06:08 PM

On fuel injected cars, when you let off the gas above a certain RPM (1500-2000) it's not injecting fuel anymore and it's just sucking in air. So no it doesn't use gas.

Any EGT or AF gauge can prove this.

Sentry

10-20-2009, 06:09 PM

Originally posted by syritis
unless your braking at the last possible second before corners and would like to be in the correct gear for exiting in efforts to reduce your lap times, i can't think of any reason why you would want to wear out your expensive clutch before your inexpensive brake pads.
I don't know what kind of downshifting you do buddy, but if you do it properly it won't wear clutch components.

89s1

10-20-2009, 06:09 PM

edit: keep reading the thread.

86max

10-20-2009, 06:10 PM

@ sentry^^ but the engine is still running is it not? So what is combusting in the cylinders to keep it running, just air?

I'm not trying to be an ass, just looking for more clarification.

89s1

10-20-2009, 06:11 PM

Originally posted by syritis
unless your braking at the last possible second before corners and would like to be in the correct gear for exiting in efforts to reduce your lap times, i can't think of any reason why you would want to wear out your expensive clutch before your inexpensive brake pads.

Its called rev matching chief, look it up. :facepalm:

Sentry

10-20-2009, 06:11 PM

The car moving in gear is what keeps the engine running.

89s1

10-20-2009, 06:12 PM

Sentry

10-20-2009, 06:14 PM

Originally posted by 89s1
then it isn't "running" either, it's just being forced through the movements mechanically.
Yeah. But when you step on the gas again or it drops below that RPM point and fuel is injected again it's ready to go.

Sentry

10-20-2009, 06:16 PM

Anyways like I said:

Originally posted by Sentry
Any EGT or AF gauge can prove this.

86max

10-20-2009, 06:16 PM

Are you talking about hybrids?

89s1

10-20-2009, 06:16 PM

Ashers

10-20-2009, 06:18 PM

On my TDI, overrunning (Engine Braking) uses no fuel at all. I know this from the sound... downshift, let off the gas, and the knocking goes away. Give it gas, knocking comes back. AFAIK, all fuel injected cars when overrun shut off all fuel injectors... it only takes a few milliseconds to get the fuel back again. I can probably log the injection quantity using vag-com on both my Golf TDI and my sisters 1.8T to see if this is correct.

Sentry

10-20-2009, 06:18 PM

Originally posted by 86max
Are you talking about hybrids?
No, I'm talking about any fuel injected vehicle since the 90s.

Originally posted by 89s1

by your logic a car uses no fuel whatsoever at idle.
No, what I said is when the engine is ABOVE a certain RPM, like say 1500 or 2000, and it's coasting it doesn't use fuel. When it drops below that it starts to inject again to keep the engine from stalling.

Sentry

10-20-2009, 06:19 PM

Originally posted by Ashers
On my TDI, overrunning (Engine Braking) uses no fuel at all. I know this from the sound... downshift, let off the gas, and the knocking goes away. Give it gas, knocking comes back. AFAIK, all fuel injected cars when overrun shut off all fuel injectors... it only takes a few milliseconds to get the fuel back again. I can probably log the injection quantity using vag-com on both my Golf TDI and my sisters 1.8T to see if this is correct.
See this guy gets it. :D

syritis

10-20-2009, 06:19 PM

Originally posted by Sentry

I don't know what kind of downshifting you do buddy, but if you do it properly it won't wear clutch components.

Depending on the brake bias i have set I do let out the clutch at a lower RPM, to slow the car faster. why not just set it with a higher rear bias and rev match perfectly? so I can down shifting through several gears (like in turn 1 at RCMP) without locking up the rears cuz not every down shift will be perfectly matched especially when you can barely shift as fast as the car slows down.

if you rev up the engine to match RPM then let out the clutch wouldn't that do the complete opposite of what the OP is trying to accomplish?

se7en

10-20-2009, 06:22 PM

okay, just to clarify the Newbs in this thread :P

engine braking using the trans causes unnecessary wear on the opposite side of the gears. What I mean is... the gears are riding on the other side of the tooth when engine braking.

It shouldn't wear your clutch since it isn't slipping either.

When the trans gears get worn on the non drive side, it makes them weaker. In some cases quite a bit since they are only heat treated on the drive side to save money[read: kia/hyundai etc]

If you have ever driven a manual car with a lot of miles, and felt that sloppy transition when going from coasting to accel, you will know what I mean.

So, to sum it all up...

Unless you are a serious tree hugger, and are worrying about asbestos, use your brakes, and wear the most inexpensive part of your car(unless running some exotic pads??) instead of wearing out your trans.

FWIW, rev matching prevents this from happening...obviously because it isn't using the engine to slow the car.

Check with any race driving school instructor if you don't believe me.

se7en

10-20-2009, 06:24 PM

Oother small thing to answer the OP question.

Nope, no gas used on a fuel injected car.

Seriously, just look at the wideband.

If it uses fuel, it isn't very much, since it reads off the scale on my innovate.(over 22:1 air fuel ratio)

89s1

10-20-2009, 06:25 PM

Originally posted by syritis

if you rev up the engine to match RPM then let out the clutch wouldn't that do the complete opposite of what the OP is trying to accomplish?

Honestly???

86max

10-20-2009, 06:27 PM

I did some reading to try and understand this more, found this interesting post:

"Wow, I was checking out the thread and I can’t believe that people are actually arguing over a common-sense concept! Engine braking is transferring the car’s kinetic momentum energy to the energy needed to overcome the engine’s compression cycle. Since the energy is moving in the opposite direction.. from the transmission to the flywheel, to the crankshaft, to the connecting rods, to the pistions, etc… there is no need for an “explosion” from the piston to overcome the next compression cycle.. the energy is already there (car in motion). To make a general statement that more RPM’s means more gas consumed is really looking at this situation blinded. You can actually cut the gas line to the engine and will continue to run at those high RPM’s as long as the car is still moving downhill. Once the car reaches flat ground it will come to a stop since the energy needed to overcome the engine’s compression will no longer be there.
Maybe the confusion with thinking RPM’s with a moving engine = gas consumption is coming from the ancient days of carburetors which are still used today on our gas powered lawnmowers. The concept there is that the gas is drawn into the cylinder by the “venturi effect” where the air intake for the engine passes over the gas line and creates a gas line suction (kind of like blowing over the top of a soda straw you can see the liquid rise up the straw). So, in this kind of engine.. YES, fuel is consumed whether the engine is actually running by combustion or by being a brake since in both cases air is still being drawn into the engine forcing gas to flow in as well.

THIS IS NOT THE CASE with fuel injection engines. With the ignition turned off ie (fuel pump and injectors not running) the only thing that is entering the cylinder if the engine is in motion from braking the car is air itself.. no fuel at all."

Sentry

10-20-2009, 06:30 PM

Originally posted by se7en
Oother small thing to answer the OP question.

Nope, no gas used on a fuel injected car.

Seriously, just look at the wideband.

If it uses fuel, it isn't very much, since it reads off the scale on my innovate.(over 22:1 air fuel ratio)
Yep, and with a pyrometer, burning fuel makes heat. If you coast the EGTs drop to zero quickly until you reach the RPM point where it start injecting again or you touch the gas, then they come back up.

pinoyhero

10-20-2009, 06:31 PM

i dont think so, although rpms rise they are just doing so because of the shift down, the absolute rpm level is less important than the relative increase or decrease assuming the same gear

benyl

10-20-2009, 06:32 PM

1. OEM brakes do not contain asbestos anymore. Some aftermarket pads do.

2. watch your injector duty cycles on decel. on any modern Fuel Injected car, they will go to zero and your AFR will peg totally lean. if you watch the IDCs, they will start to go up again as the RPM reach idle.

What does that mean? A modern fuel injected car uses no fuel on decel.

89s1

10-20-2009, 06:32 PM

Originally posted by Sentry

Yep, and with a pyrometer, burning fuel makes heat. If you coast the EGTs drop to zero quickly until you reach the RPM point where it start injecting again or you touch the gas, then they come back up.

Looks like I'm old school and need to start refreshing the fundamentals I learned from dear old dad way back when.

I stand Corrected. Sentry, I owe you a beer. :thumbsup:

BrknFngrs

10-20-2009, 06:33 PM

^^ While the post does make sense wouldn't that mean that leaving a car idling would result in it running incredibly lean (ie: 100% lean) which would destroy the motor?

edit: i was referring to the long post up top, lots of post were made while I was posting mine.

Sentry

10-20-2009, 06:34 PM

Originally posted by 89s1

Looks like I'm old school and need to start refreshing the fundamentals I learned from dear old dad way back when.

I stand Corrected. Sentry, I owe you a beer. :thumbsup:
Any time. :D

dj_honda

10-20-2009, 06:39 PM

actually, some of the newer cars, the injectors do stay on, but only with a small pulsewidth. and the reasoning is to keep combustion happening so that your catalytic coverter does not cool down to the point of being innefficient. so basically for emissions purposes.

Sentry

10-20-2009, 06:40 PM

dj_honda

10-20-2009, 06:42 PM

Originally posted by Sentry

OBDII and newer cars, right?

yeah i think so.

Kavy

10-20-2009, 09:08 PM

Originally posted by dj_honda

yeah i think so.

You are right.

revelations

10-20-2009, 10:00 PM

Originally posted by dj_honda
actually, some of the newer cars, the injectors do stay on, but only with a small pulsewidth. and the reasoning is to keep combustion happening so that your catalytic coverter does not cool down to the point of being innefficient. so basically for emissions purposes.

I'm running a Scangauge 2 unit in my 02 civic.

It shows 0.0 litres per hour of fuel consumed when I let my foot off the gas while in gear - presumably the amount of fuel
used to keep some combustion going is smaller than the ECU is able to measure in this case as thats what its reporting (eg. it could be 0.04 LPH)

This is a MANUAL TRANSMISSION car BTW.

Sugarphreak

10-20-2009, 11:13 PM

....

Kavy

10-20-2009, 11:53 PM

^
So engine breaking causes no additional wear on the transmission, this is fact because you have never had to replace a transmission.

Brake pads last 100,000km, this is fact because it happened to you.

Your personal experience has lead me to believe your statements are fact.

Additionally it has lead me to believe everyone else who had experiences must be wrong, because they are not you.

Godfuader

10-21-2009, 12:28 AM

Neutral Coasting in the summer (saves fractional gas)
Engine braking in the winter (better than hitting brakes on ice)

ReflexFX

10-21-2009, 12:43 AM

Originally posted by 89s1

Its called rev matching chief, look it up. :facepalm:

How do you downshift rev match without stepping on the gas and wasting it?:poosie:
Then, if you decide not to waste gas and downshift without rev matching, then you're wearing your clutch.

89s1

10-21-2009, 01:15 AM

Originally posted by ReflexFX

How do you downshift rev match without stepping on the gas and wasting it?:poosie:
Then, if you decide not to waste gas and downshift without rev matching, then you're wearing your clutch.

All he mentioned was burning the clutch :dunno:

Kardon

10-21-2009, 01:46 AM

This was a pleasing argument.

alloroc

10-21-2009, 06:47 AM

I play around with mile hypermiling on occasion just for kicks and watch my fuel consumption gauge.

Double clutching and rev matching the down shifts does not make you use as much fuel on long decelerations (1/2 block or more) as neutral coasting. You also do not need to be engine braking as much as you think. Even picking a gear with the revs between 1500 and 3k rpm while slowing down is enough for my gauge to show 0.2 L/100k - this is as low as my OEM gauge will go. Neutral coasting is advantageous down long shallow hills where you will hold your speed. Without any real effort or reducing driving times. The biggest gas saver is short shifting during acceleration.

theken

10-21-2009, 07:42 AM

Transmissions fail from coasting in gear? Wow.

revelations

10-21-2009, 12:07 PM

I dont generally bother with downshifting.

Eg. if I am in 4th gear and coming up to a fresh red light, I will just let off the gas and the fuel will cutoff until the engine returns normal idle rpms at which point I push the clutch in.

Brakes are consumables, clutches and (to a lesser extent) transmissions, not so much.

Kloubek

10-21-2009, 12:24 PM

Personally, when I drive, I use all the tools given to me to drive in a manner which makes me most "at one" with the car.

This means utilizing engine braking.

I've owned 26 cars in my lifetime, and the only transmission failures I've ever experienced were on automatics. I have indeed had to replace a couple of clutches, but that is pretty expected when you drive aggressively like I tend to with sporty cars.

No, I am not claiming my personal experiences necessarily accurately reflect a lack of wear on a transmission... but they are indeed conclusive enough to ensure I will not be changing my driving habits any time soon.

As far as engine braking using up gas or not using up gas - I really could care less. Even if it did, the amount would be negligible considering 95% of driving is while your car is in steady motion. Unless you drive the Deerfoot daily.... in which case only 5% of your driving is steady motion.

Sugarphreak

10-21-2009, 12:34 PM

...

scat19

10-21-2009, 02:36 PM

Originally posted by revelations
I dont generally bother with downshifting.

Eg. if I am in 4th gear and coming up to a fresh red light, I will just let off the gas and the fuel will cutoff until the engine returns normal idle rpms at which point I push the clutch in..

Wow, even the "car savy guys" of beyond can't drive standards.

What if a car came out of no where, and you wanted istant power to switch lanes or something?

4th gear, at 30Km/h, and your RPMS are around 1000. Not going to happen is it.

When down-shifting, rev-match so you don't wear your clutch out.

My car is ALWAYS in gear (except red lights, don't want to wear the clutch spring so it's out in N) for safety and manueverability.

If you did that coast/keep it in 4th without downshifting, you'd fail your advance road test.

And also, to people who downshift without rev-matching - A) it's slow, b) it ruins your clutch, c) learn to drive!

FiveFreshFish

10-21-2009, 02:41 PM

Originally posted by alloroc
0.2 L/100k - this is as low as my OEM gauge will go.

Two of my cars go right down to zero.

Sentry

10-21-2009, 02:46 PM

Originally posted by scat19
My car is ALWAYS in gear (except red lights, don't want to wear the clutch spring so it's out in N) for safety and manueverability.
That reminds me, I think it's a law that you have to keep a manual trans car in gear all the time, no coasting in neutral.

But yeah mine's in neutral at red lights. Your throwout bearing and pressure plate fingers last longer that way since they're not in contact with one another. Plus who wants to sit there holding the clutch down for a minute or two.

scat19

10-21-2009, 03:03 PM

Originally posted by scat19
If you did that coast/keep it in 4th without downshifting, you'd fail your advance road test

Originally posted by Sentry
That reminds me, I think it's a law that you have to keep a manual trans car in gear all the time, no coasting in neutral

:thumbsup:

Gibson

10-21-2009, 05:29 PM

Originally posted by Sentry

That reminds me, I think it's a law that you have to keep a manual trans car in gear all the time, no coasting in neutral.

This is a true fact, a lot of people I talk to don't believe me. It is, however, impossible to enforce so it doesn't really matter at all.

I'm with scat on this...my car is always in gear, down hills, around corners, coming up to stop lights.

I believe the "proper" way to drive manual involves rev-matching and downshifting. Without it, you're not really driving in the correct fashion.

Which reminds me, does anyone know if rev-matching is possible in cars like the Cobalt SS that have no-lift shifting?

FiveFreshFish

10-21-2009, 05:48 PM

Proper driving techniques > additional mechanical wear

sr20s14zenki

10-21-2009, 05:55 PM

Just out of curiosity, can somebody explain why my powerFC shows 0% duty cycle when im in decel? Wouldnt this mean that there is no fueling going to my injectors? or is it just lying? Or perhaps the amount of fuel thats going in is so small it doest register? I dunno, cuz it idles around 1.5% duty cycle....

5000Audi

10-21-2009, 06:12 PM

Originally posted by Gibson

Which reminds me, does anyone know if rev-matching is possible in cars like the Cobalt SS that have no-lift shifting?

pretty sure you can, as the no lift shift just keeps the engine from going to redline, kinda like launch control.. but hitting the gas while in "N" will make the rpms go up..

***EDIT***

oh yeah and btw, my 86 audi has the fuel cut off on decel too.. so its not just "modern cars" and the audi isnt even EFI its just FI

se7en

10-21-2009, 07:15 PM

For the record...and I am not going to post again...

It won't cause your trans to fail. It will however cause it to get more sloppy.

To the above poster who when 480,000 kms on his trans driving 'his' way...I can only imagine how awesome it shifted and transitioned between accel and decel.

Reminds me of the old grain trucks....vrrrrrooooommmmm....pause pause pause brrrrrr(decel).........wait for it......pause pause....vvvvvv----rbrbrbrbr---broooommm....

lol, I had to add some text to sound effects to this one.

Just think about it logically.

I guess if you don't mind it, do it. But if races are wanted to be one.....and no, I don't mean street racing...geez.

Sugarphreak

10-21-2009, 07:37 PM

...

theken

10-21-2009, 08:05 PM

shifters get "sloppy" cause the "gates" (i think that is what they are called) are made of plastic and wear out, thats the side to side motion you feel, nothing to do with coasting in gear

962 kid

10-21-2009, 08:11 PM

Originally posted by sr20s14zenki
Just out of curiosity, can somebody explain why my powerFC shows 0% duty cycle when im in decel? Wouldnt this mean that there is no fueling going to my injectors? or is it just lying? Or perhaps the amount of fuel thats going in is so small it doest register? I dunno, cuz it idles around 1.5% duty cycle....

Read the thread :dunno: fuel cut on decel = no fuel being injected

Originally posted by se7en
For the record...and I am not going to post again...

It won't cause your trans to fail. It will however cause it to get more sloppy.

To the above poster who when 480,000 kms on his trans driving 'his' way...I can only imagine how awesome it shifted and transitioned between accel and decel.

Reminds me of the old grain trucks....vrrrrrooooommmmm....pause pause pause brrrrrr(decel).........wait for it......pause pause....vvvvvv----rbrbrbrbr---broooommm....

lol, I had to add some text to sound effects to this one.

Just think about it logically.

I guess if you don't mind it, do it. But if races are wanted to be one.....and no, I don't mean street racing...geez.

Thank god this is your last post, because you are really clueless
:thumbsup:

sr20s14zenki

10-21-2009, 08:17 PM

Originally posted by 962 kid

Read the thread :dunno: fuel cut on decel = no fuel being injected

Thank god this is your last post, because you are really clueless
:thumbsup: yah I know how efi works hahah. I wanted to see the people that say fuel keeps going, explain it... For a laugh. I was trying to approach it in a humble manner.

962 kid

10-21-2009, 09:33 PM

:facepalm: my bad, I should have caught that haha.

psycoticclown

10-21-2009, 09:44 PM

How about downshifting in an automatic with a manumatic more, is it bad for the tranny?

Ashers

10-21-2009, 09:54 PM

Logged my Jetta today... and guess what? Fuel is shut off during overrun.

Wednesday,21,October,2009,16:43:12:40450
VCDS Version: Release 908.1
Data version: 20091018

--------------------------------------------------------------------------------
--------------------------------------------------------------------------------

Address 01: Engine (06A 906 032 CM)

16:43:07 Group 002: At Idle
1120 /min Idle speed 700-820 rpm
21.8 % Engine load 15-25%
2.46 ms Inj. period 2.0 - 4.0 ms
5.72 g/s Air mass in 2.0-4.5 g/s

Wednesday,21,October,2009,16:53:45:40450
VCDS Version: Release 908.1
Data version: 20091018

Address 01: Engine (06A 906 032 CM)

16:53:34 Group 005: At Idle
2240 /min Idle speed 700-820 rpm
9.8 % Engine Load 15-25%
80.0 km/h Vehicle Speed 0 MPH
Overrun Oper. Cond Idle

16:53:34 Group 002: At Idle
2240 /min Idle speed 700-820 rpm
9.8 % Engine load 15-25%
0.00 ms Inj. period 2.0 - 4.0 ms
4.64 g/s Air mass in 2.0-4.5 g/s

sr20s14zenki

10-21-2009, 10:02 PM

Of course it is. There is no reason to have fuel present when your drivetrain is turning the engine. When your ecu sees that your throttle angle is zero and your rpm are above the set point, it realizes you are in decel. When it sees the proper rpm for idle it triggers the fuel back on because it knows it's idle time. My powerfc actually allows me to adjust those triggers a bit. It allows me to set when to cut fuel and then add it again. Mine is set to cut at 1300 and come on again at 1000. Helps with maf and big ic/turbo reversion issues.

johnboy27

10-22-2009, 11:57 PM

Originally posted by Sugarphreak
^^^^

Ditto...

Why somebody would buy a manual car and then coast to a stop is beyond me.

Depends on the car; but generally yeah they basically shut down when you gear down. I know that my car shuts them off completely while engine braking.

I would say it is fact because of almost non-existant manual transmission failures due to this cause... I can't think of a single person who has ever replaced thier manual tranmission due to this. It actually borders on absudity to even suggest your transmission would fail due to this.

Yeah 100,000km brake pads keep happening to me consistantly accross a half a dozen cars; take what you want from that. I watch most automatics burn through them in a quarter of that distance.
I'm in the same boat, I rarely ever have to replace brake parts or transmission parts. I have 146,000 km's on my stock original brakes, clutch and transmission. I engine brake all the time, rev match and then coast in gear until I am close enough to the stop sign or I have to accelerate at the bottom of a hill.