Best habit to shift gears on MT and fuel economy

[supramkivtt2jz]

Originally Posted by N1rve

Under 3000!? I get my car in the 3-4k range...right now I'm averaging 27 MPG LOL

...and i shift at 2500. i get 35+ mpg hwy and 28ish around town

[Pete156]

Originally Posted by strat61caster

http://en.wikipedia.org/wiki/Energy-...ing_or_gliding



The technology has been around for at least 20 years. You bet your ass the fuel injectors stop injecting fuel when coasting in gear, or at least a significantly reducedamount.

Here's a paper from 2009 where the abstract talks about how (5 years ago) modern vehicles use almost zero fuel whilst coasting:
http://papers.sae.org/2009-01-0416/

I tried to find the original paper proving fuel shutoff was possible and beneficial but no luck.

"Significantly reduced" and "almost" are not equivalent to Zero, Zilch, Nada, NO FUEL WHATSOEVER.

This is my only point. There is some amount of fuel being used while coasting in gear, regardless of how little.

[strat61caster]

Originally Posted by Pete156

This is my only point. There is some amount of fuel being used while coasting in gear, regardless of how little.

Ah, I misunderstood. I thought you were defending the following post:

Originally Posted by Pete156

Sorry, but you are wrong about coasting in gear. When you coast in gear, you do consume gas. If you didn't, your engine would stop running. The amount of fuel is indeed much less, but the engine is still burning fuel while coasting in gear. Even an engine driven by the wheels burns gas.

Which I took to mean that you did not believe that coasting in gear resulted in fuel savings. It most certainly does. Glad we're on the same page.

[chrisl]

Originally Posted by Pete156

"Significantly reduced" and "almost" are not equivalent to Zero, Zilch, Nada, NO FUEL WHATSOEVER.

This is my only point. There is some amount of fuel being used while coasting in gear, regardless of how little.

And that is incorrect. With the majority of modern cars (possibly all of them), the injectors are turned off when coasting in gear. The engine becomes an air pump. There's no reason why you would need to be burning any fuel - the engine is kept running by the driveline.

[Photonic]

Originally Posted by chrisl

And that is incorrect. With the majority of modern cars (possibly all of them), the injectors are turned off when coasting in gear. The engine becomes an air pump. There's no reason why you would need to be burning any fuel - the engine is kept running by the driveline.

I was just sayin this then pete made me go ...wtf ...so I deleted it and now im sayin it again cuz I figured maybe it was just on my old 240.

Injector Pulse width is 0 Milliseconds in gear and 0 throttle. ...look at your fuel and timing maps. pretty sure all cars use this same type of idle air protocol and its why you usually have some tyoe pf idle air control valve to compensate for this fact when the car is in neutral and unable to maintain RPM due to driveline.

The computer recognizes a stall condition and switches to an idle protocol and begins injecting fuel

[dssence]

Originally Posted by Photonic

I was just sayin this then pete made me go ...wtf ...so I deleted it and now im sayin it again cuz I figured maybe it was just on my old 240.

Injector Pulse width is 0 Milliseconds in gear and 0 throttle. ...look at your fuel and timing maps. pretty sure all cars use this same type of idle air protocol and its why you usually have some tyoe pf idle air control valve to compensate for this fact when the car is in neutral and unable to maintain RPM due to driveline.

The computer recognizes a stall condition and switches to an idle protocol and begins injecting fuel

hmm kay , so what would be the best habit when you reach to a red light. I always shift my manual to neutral when I'm coming to a stop. In that case I will be consuming more fuel? .. what would be the best thing to do.
I don't understand when you guys say to cruise in gear, if had to cruise in gear you would have to keep the clutch pressed for the car engine not to turn off. Help me here.

[Photonic]

Neutral = has to be added. Stay in gear until you need the engine to idle. again coasting in gear = 0 injector activity as long as you do this.

But really ...its not that big a deal o.O. ..other factors affect your gas mileage so much more you may not even "notice" the benefit ..but there "is one"

its like making your car lighter. yes ...removing your floor mats DOES ...save weight. But you could remove your spare tire instead *shrug*. This is kind of like that ..yes it uses no fuel to coast in gear ..but just doing it up to stoplights?? thats like pulling those floor mats out for weight reduction.

[dssence]

Originally Posted by Photonic

Neutral = has to be added. Stay in gear until you need the engine to idle. again coasting in gear = 0 injector activity as long as you do this.

Kay I understand I've seen some technical data about the injectors using pulse width modulation and with an oscillopscope it's being a square wave. And when they're in neutral it keeps pulsating so fuel is being pumped.
So this principle applies to injectors in cars not with old carburator cars, right?
Now so if I had to come to a stop in a red light I should have to keep the clutch pressed,stop and while keeping the clutch pressed leave the gearbox in 1st gear? I would end up screwing up the clutch life this way.

[Pete156]

Originally Posted by chrisl

And that is incorrect. With the majority of modern cars (possibly all of them), the injectors are turned off when coasting in gear

And they start pumping again if I engage the clutch coasting in gear?

[Photonic]

Originally Posted by dssence

Kay I understand I've seen some technical data about the injectors using pulse width modulation and with an oscillopscope it's being a square wave. And when they're in neutral it keeps pulsating so fuel is being pumped.
So this principle applies to injectors in cars not with old carburator cars, right?
Now so if I had to come to a stop in a red light I should have to keep the clutch pressed,stop and while keeping the clutch pressed leave the gearbox in 1st gear? I would end up screwing up the clutch life this way.

no ..leave the clutch out lol ....you want the wheels connected to the engine ..the wheels are turning the engine as an air pump ...if you put the clutch in the injectors pulse just like any normal idle to keep the engine running

[Photonic]

Originally Posted by Pete156

And they start pumping again if I engage the clutch coasting in gear?

Yes ... if you push in the clutch it is the same as neutral ..how can the engine not drop to 0 without the wheels connected to the tranny and flywheel ... it has to add gas ...

[cycleboy]

I'm still getting ~31mpg after 14K miles.

A lot of that has to do with my typical drive:

1 mile of 35mph city streets, 33 miles of 65-75mph open highway, 1 mile of 45mph city streets. In the afternoon, do it in reverse. Do this 5X per week.

But, it also has to do with how I drive. I usually shift it in the 4-5K range, except the occasional times having fun when I take it up to 6K+. Once I'm at cruising speed, I tend to put it in a gear that keeps the revs in the mid 3's (so 5th gear for ~45mph, 6th gear for 75mph). This is sort of like overdrive on an auto. Your revs drop and you have no acceleration, but better mileage and quieter. If I need to accelerate, downshift!

I think if I was DD'ing it like I am but always shifting north of 6K and leaving it in gears where it is high in the rev range (and powerband), I'd probably have some sucky mileage.

[dssence]

Originally Posted by cycleboy

I'm still getting ~31mpg after 14K miles.

A lot of that has to do with my typical drive:

1 mile of 35mph city streets, 33 miles of 65-75mph open highway, 1 mile of 45mph city streets. In the afternoon, do it in reverse. Do this 5X per week.

But, it also has to do with how I drive. I usually shift it in the 4-5K range, except the occasional times having fun when I take it up to 6K+. Once I'm at cruising speed, I tend to put it in a gear that keeps the revs in the mid 3's (so 5th gear for ~45mph, 6th gear for 75mph). This is sort of like overdrive on an auto. Your revs drop and you have no acceleration, but better mileage and quieter. If I need to accelerate, downshift!

I think if I was DD'ing it like I am but always shifting north of 6K and leaving it in gears where it is high in the rev range (and powerband), I'd probably have some sucky mileage.

Can you clear something up for me , will this car adjust fuel more efficiently if I shift gear in the order of 4-5K range like you said? versus shifting in the 2-3k range? . I know the D4S has 1 injector and a port injector how do those 2 work in symmetry. If I would come up to know the rpm's where the injectors are working more efficiently would be a huge step forward. If anyone does know

[SalM]

Originally Posted by N1rve

Under 3000!? I get my car in the 3-4k range...right now I'm averaging 27 MPG LOL

This 10000000000% . Im ranging about 24-26 MPG