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Discussion Starter · #1 ·
Just thought I'd post this note due to the fact that I did it with our 2004 one day thinking I'd just save a tiny drop of fuel down a very long incline by coasting. Some of the old Saab cars actually had a freewheel feature built in, man the old 96 was a hoot, I always wanted one but at the time could not afford any car.

Back to the XC90 with AWD and DSC, when I shifted into neutral and the car started to coast, something in the system thought the car was out of control and man I have to tell you, I thought the drivetrain was about to be ripped out from under me. I think the brakes were being applied or something and I quickly shifted back into drive and we continued. My wife gave me THE LOOK like WTF are YOU doing NOW.

So basically if you do shift into neutral while underway, be prepared for a potentially huge repair bill.

best,

P
 

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Something similar happened to me in my first V70R a few days after I bought it. I decided to shift into neutral while coming to a stop and all these service required messages started appearing on my dash and the car went into limp mode.. it scared the hell out of me! I pulled over, restarted the car and everything was fine again. Now I drive a manual R =)

I've never had any issues shifting into neutral on the roll in any of my previous cars.
 

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must be specific to automatics?

Sent from my rooted, rommed Galaxy Nexus....
 

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Discussion Starter · #4 ·
My advice to any XC90 owner, is to "don't do it". Maybe GrecianVolvo can put some daylight on this issue, but I think it has something to do with the Directional Stability Control system, maybe thinking the car is out of control or something.

I tried to climb a steep hill in the snow one day with the DSC system activated and it was a real mistake. The wheel slippage made the system think the vehicle was out of control and it shut me down in a real bad location, i felt like a cat hanging on the drapes half-way between the floor and the ceiling, and the car then slid backwards with all 4 wheels locked and narrowly missed hitting a tree. Later I learned to turn off the DSC system and let those wheels spin freely to gain the maximum climbing capability and was able to get up the hill.

Not accustomed to having a car second guess why I want to spin the tires, and then take action to compensate for it.

Best,

P
 

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That's odd that you folks have been having problems - on mine I will occasionally shift into N, turn off the engine, turn it back on, and back into D while the car is moving at freeway speeds, and I've never encountered a problem.

I do that every now and then because the fuel gauge occasionally displays empty when I know there is fuel in the tank - this is how I reset it.
 

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interesting, howd you figure that was the way to reset?

Sent from my rooted, rommed Galaxy Nexus....
 

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Not saying I recommend to reset it that way, but I'll notice that while the engine's cranking, the dash loses power which should be normal. However, after power is restored to the dash after the engine starts, sometimes the fuel gauge stays in the "powered off" position at empty. If I remember to check before I start driving, then I can just turn off and restart the engine while parked and it resets it.

Otherwise, when I glance down when I'm on the freeway, I'll do the routine while the car is moving. Not recommended, because while the engine is off you have NO POWER STEERING but the vacuum pump should be able to provide a good reserve for your power brakes. AGAIN, NOT RECOMMENDED.

That being said, I have never encountered any problems doing this while the car is moving.

Also in response to Mr. P - modern cars (and by modern, I mean the vast vast majority of fuel-injected cars) actually shut off the fuel injectors when coasting with your foot off the gas. When you pop it in neutral to coast you will actually use MORE fuel because now the injectors have to fire to maintain the engine idle. I have no definitive proof of this on the Volvo, but on my Subaru if I plug my laptop in and watch the injector duty cycle, I can prove this.
 

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Also in response to Mr. P - modern cars (and by modern, I mean the vast vast majority of fuel-injected cars) actually shut off the fuel injectors when coasting with your foot off the gas. When you pop it in neutral to coast you will actually use MORE fuel because now the injectors have to fire to maintain the engine idle. I have no definitive proof of this on the Volvo, but on my Subaru if I plug my laptop in and watch the injector duty cycle, I can prove this.
So in the subaru at least when coasting you are in effect engine braking (the engine most still be rotating in order for it fire once you step on the gas or come to a stop), v shifting into neutral and coasting. I wonder how much loss you have in engine braking compared to shifting into neutral and free wheeling, does that make up for the fuel burned while in neutral? In a manual car there is a discernible difference in the decel rate if you let your foot off the gas (with out shifting into neutral, or disengaging the clutch) to coast v. shifting into neutral to coast. Also, have you checked on the Subaru to see what the duty cycle is with the engine just idling? I hate things measured in percentages because, unless you know how the percentage is calculated you only have a relative scale.
 

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Saab's interest in free-wheeling (non-braking) engines was centered around the fact that their early engines were two-cycle, i.e., ...no fuel = no lubrication. If one braked with his two-cycle engine down a very long slope ... he could arrive at the hill's bottom sans engine! The one-way clutch you could hold in the palm of your hand ... not large enough for the duty.
 

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Not saying I recommend to reset it that way, but I'll notice that while the engine's cranking, the dash loses power which should be normal. However, after power is restored to the dash after the engine starts, sometimes the fuel gauge stays in the "powered off" position at empty. If I remember to check before I start driving, then I can just turn off and restart the engine while parked and it resets it.

Otherwise, when I glance down when I'm on the freeway, I'll do the routine while the car is moving. Not recommended, because while the engine is off you have NO POWER STEERING but the vacuum pump should be able to provide a good reserve for your power brakes. AGAIN, NOT RECOMMENDED.

That being said, I have never encountered any problems doing this while the car is moving.

Also in response to Mr. P - modern cars (and by modern, I mean the vast vast majority of fuel-injected cars) actually shut off the fuel injectors when coasting with your foot off the gas. When you pop it in neutral to coast you will actually use MORE fuel because now the injectors have to fire to maintain the engine idle. I have no definitive proof of this on the Volvo, but on my Subaru if I plug my laptop in and watch the injector duty cycle, I can prove this.
Just FYI., my fuel gauge would do the same thing to me late last year and after several months of having to reset the fuel gauge (when it would read empty) by turning the car off, the entire ECM failed and it went into limp mode and got all sorts of error messages. I was 800 miles from home btw and had it towed to a local dealership who replaced the ECM and havnt had the problem since.:rolleyes:
 

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Back to pengc99's bizarre and dangerous ritual of turning off the engine while moving...
have you ever tried to turn the steering wheel with the engine off ?
When my alternator died and it needed a tow home, the front wheels were turned quite a bit and the engine wouldn't fire up again to get it on the flatbed. Most cars steering will turn with some added difficulty but this was ridiculously hard to turn. Thought it might even do some damage.
Makes me wonder how the electric steering on a lot of new vehicles handles this situation.
 

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Turning most cars w/o the help of power steering is not that bad once you get them up to speed. At the speeds of being put on a tow truck or parked most of the resistance is from the tire:ground interface. On the cars with E-power steering I assume that there is still a mechanical link between the wheels and steering wheel, so I would imagine it would be tolerable. I do not look forward to the day when the steering wheel is nothing more than an optical encoder and then a linear motor turns the wheels, but it is coming just like throttle cables. The need to save weight to save fuel is ever present.
 

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Back to pengc99's bizarre and dangerous ritual of turning off the engine while moving...
have you ever tried to turn the steering wheel with the engine off ?
When my alternator died and it needed a tow home, the front wheels were turned quite a bit and the engine wouldn't fire up again to get it on the flatbed. Most cars steering will turn with some added difficulty but this was ridiculously hard to turn. Thought it might even do some damage.
Makes me wonder how the electric steering on a lot of new vehicles handles this situation.
I have driven plenty of cars with no power steering before so I was prepared for the dramatic increase in steering effort without the power assist.
 

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Our Saab 96 was not a 2 cycle and had freewheel. Please explain.
 
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