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hey guys... jsut a quick question here, im tryin to cut down on gas expenditure and basically wanna save as much as possible.. so i occasionally switch from D to the N (drive to neutral) a friend of mine told me that doing that too often will screw up ur transmission box and thought id get some feedback on the matter. if so then wht can i do ? thanks
 

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I don't think that saves gas. All it does is disengage the power going to the wheels. The engine is still churning away. I could be wrong.
 

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hey guys... jsut a quick question here, im tryin to cut down on gas expenditure and basically wanna save as much as possible.. so i occasionally switch from D to the N (drive to neutral) a friend of mine told me that doing that too often will screw up ur transmission box and thought id get some feedback on the matter. if so then wht can i do ? thanks

I can't see that hurting the transmission....your only switching gears..I would assume the only wear and tear would be putting into drive rolling?

Anyway, I don't think this would make a shred of gas mileage savings..

- Mark
 

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This reminds me of extreme hypermile techniques. From Wikipedia:
Generally, the recommended way to hypermile is using only the common techniques. However, extreme hypermilers have been known to use controversial and illegal techniques:

  • drafting behind trucks, decreasing awareness of the road ahead and increasing the possibility of a rear-end collision
  • driving far below the speed limit at times, disrupting the normal flow of traffic
  • taking sharp curves at high speeds to avoid losing energy to braking
  • coasting with the engine off, with the resulting loss of power steering and power brakes
  • passing or rolling through red lights or stop signs in areas of low traffic
  • over-inflating tires to reduce rolling resistance, sometimes to twice the manufacturer's specifications or more
I only do one of these... :D

I don't see any mention of coasting in neutral for normal or extreme hypermile techniques. You may save some gas, but it may be too small to see in one tank full.
 

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Discussion Starter #5
well yeah the car would b coasting at around 60 or 90 , but i dnno. im just tryn to figure smthn out here :)
 

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The worst wear on a transmission is slippage. Slippage is the slipping of clutch material against one another as the clutches fight to match the speeds of two transmission elements, whatever they may be. This kind of slippage normally happens during shifts of any kind, as the new gear ratio needs to be "enforced" within the transmission (engine RPM changes to reflect the new relationship with the road speed).

Every time you shift into D, you provoke a "shift". You induce slippage. You promote wear of the clutch material. Whatever small mileage improvement you get from removing the small parasitic drag of the torque converter on the engine with the vehicle at rest, you probably will end up paying in transmission wear in the long run and more.
 

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Oh, if you are doing this at speed, remember that transmission fluid pressure is provided by an internal pump that is usually driven by the input side, ie. engine RPM. Running 60 mph with the engine at idle RPM is probably not a great idea for an automatic transmission.

It's one of the reasons why towing a RWD car with the rear wheels on the ground is not a good idea unless you disconnect the driveshaft.
 

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It's a fact that while in neutral, the engine uses fuel to keep it at idle speed. Left in D, all fuel is shut off as the revs build using NO fuel. So leaving it in drive uses less fuel.
 

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It's a fact that while in neutral, the engine uses fuel to keep it at idle speed. Left in D, all fuel is shut off as the revs build using NO fuel. So leaving it in drive uses less fuel.
Not in all scenarios. Fuel cutoff on deceleration is only used in some situations where RPMs and gear ratio permit. Most of the time this will not occur (seems to need RPM to be significantly above ~2200 RPM and this only lasts until a few hundred RPM above idle). If you have a modified exhaust path you will certainly hear the transition into this mode. It's an awesome sound on an injected V8!!

But as you mentioned this can only occur in gear (not just [D]).

Besides, leaving it in [D] will allow for the transmission to overrun when necessary with minimal engine drag so there shouldn't be any perceptible improvement over having the engine drop to idle in neutral with the car moving.


(also, with electronic controls, you will notice that engine RPM will actually hover a few hundred RPM above idle when the car is at speed but in neutral... this is likely incorporated into the PCM as a way to maintain enough rotation to the power steering pump and alternator and A/C, not to mention possibly trying to save the transmission. So the gain, if any, becomes increasingly minimal)
 

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Sorry to interrupt your thread here DarkShocker.

TTA, as always your info is impressive. Question for you: Ford advertises for their new trucks in an effort to improve fuel economy, the moment you release the gas pedal all fuel shuts off...How do you think they got around what you wrote above? not challenging what you wrote, just curious.
 

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if you want to improve your car's gas mileage, the answer is simple -- make sure that your car's fuel system is clean from the inside.

check if it's fuel filter is clean. if it needs to be replaced, replace it.:driving:

also, check the ignition system of your car because a perfectly conditioned ignition can help you save gas. i've read it somewhere before. :)
 

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I honestly don't know what's unique about Ford's fuel shutoff. You got my curiousity going, so I google'd it and came up with this entry:

http://media.ford.com/article_display.cfm?article_id=28869

Vague marketing-type stuff. In it, I can't really read anything that sounds unique and "revolutionary".

Fuel-cutoff was even used on my 1987 GTA... for years, I was intrigued by the change in the exhaust note at certain times during deceleration (as well as seeing some unexplained RPM behaviour related to torque converter clutch operation). I couldn't explain why deceleration in D (not [D] or "OD", which provides less engine braking on GM trannies) produced occasional surges... the RPM would hold while the car decelerated, then occasionally the TCC felt like it unlocked and the RPM dropped a bit while the exhaust note changed a tiny bit (still engine-braking, due to the overrun clutch applied in D) then would climb a bit again as the TCC locked again and the sound would be detectable again... and so on as the car slowed. Hooking up a scan software showed that the injector pulse-widths were being commanded to 0 during these periods, confirming injector shut down. (the cycling on-off of this shutoff was probably to prevent excessive cool-down of the cat converter, I guess)

Same with my WS6... rev above 2200 or so in gear, let off and wait a second or two MAX and the exhaust note changes. Scan software shows a dramatic drop in injector pulse width but not "0" like on my GTA, but on the other hand the "cutoff" here will hold until a hair before idle (say, around 1000 RPM) at which point the injectors come back to life. The difference in pulse width is VERY noticeable versus when you begin deceleration from a point below 2000 RPM, as is the exhaust note.

Have a listen to the following recording I made back in the early 2000s... it's not terribly exciting but it shows what I hear in the cabin in normal driving.
http://www.tripletransam.com/WS6/media/ws6rev_1.mp3
Note at 0:15 I think I'm in second gear and fuel cutoff kicks in as I've started deceleration from around 2300 RPM or so. At 0:17 you'll hear me get very lightly back on the gas pedal and there is a resulting POP from the exhaust system as unburnt fuel from the injector restart ignites in the hot exhaust. You can hear fuel cutoff end at 0:32 as the engine reaches *just* above idle. Etc.

You can also hear it here... including both times when I get back on the gas ("pop"). The reactivation at the end of the video is noticeable.
http://www.youtube.com/watch?v=CGlS4VT9WI0

So what's the big deal with Ford's implementation? I honestly don't know... except that the Ford transmissions I've experienced (4R70W, etc.) don't use any overrun clutches. GM 4-speed auto trannies when left in OD or [D] (depending on model and year) will allow the full 1-2-3-4 progression, with little engine braking in any of the higher gears... when in 3 or D, they lockout the overdrive gear and only allow 1-2-3 BUT they also apply an overrun clutch in 3rd. This keeps the engine RPM higher and provides engine braking, at the expense of fuel consumption of course. Anyway, the 4R70Ws I drove all allow the RPM to plummet to near idle when you let off the gas. Cutting fuel at this point would cause an immediate stall... there'd be very little transmission of road movement to the engine to keep it rotating.

So maybe Ford "engineering" (I use the term loosely) implemented a way to get their transmission to "lock up" and keep the engine rotating on strong deceleration while allowing normal free-running at low throttles, and allowing for a quick smooth transition between full "lock up" during deceleration and unlocking (partial or otherwise) during acceleration. For sure this would need complex and tight timing to avoid clunking or hesitation. Maybe this is where the big deal is: allowing Ford to integrate something that's been out for 25 years with their drivetrain design. Just a wild guess.
 

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Unless things have changed, you might have a hard time getting it back into gear while moving at any significant speed. It's one of those "protect the transmission at all costs" programming deals. Sometimes you have to pull over and almost stop.
 

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instead of playing with the tranny
watch your starts and stops
combine trips to drive less
 

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Also, coasting in neutral, whether with automatic or standard transmission is generally not a good idea as you might suddenly need power (throttle response) in an emergency. You don't want to bumble around to get it ba k in gear.
 
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