Coasting with an Auto

[SVOboy]

Originally Posted by Compaq888

your tranny must be designed differently than mine. I'm still getting good mpg with coasting in D. Whenever you let your foot off the gas the tranny goes automatically into neutral, the reason the car slows down so much is it's connected to the engine. When you put the lever in N you actually disengage the tranny from the engine and you get a longer coast because your engine is not slowing down the tranny.

It's actually pointless to just stick it in N and coast because the engine still injects fuel. If you're going to stick it to N you better shut off the engine to save fuel. On my car if it's in D and I coast the fuel injection shuts off till like 1000-1100rpm then comes on to prevent the engine from stalling.

You can find out a lot by reading a FSM for your car. If you have one look in the Electronic control section.

From the sound of it your car is a freak. My car does not do this. Anyway, in an automatic, from my understanding, the engine is never actually really connected to the tranny unless isn't fully locked up. My tranny does shift automatically into neutral, but it'll drop revs as the torque converter does it's thing to act independently of the engine.

Rick has said neutral coasting is much better than in gear on his auto, I think it's up to everyone to figure that up for themselves.

[Compaq888]

Originally Posted by SVOboy

From the sound of it your car is a freak. My car does not do this. Anyway, in an automatic, from my understanding, the engine is never actually really connected to the tranny unless isn't fully locked up. My tranny does shift automatically into neutral, but it'll drop revs as the torque converter does it's thing to act independently of the engine.

Rick has said neutral coasting is much better than in gear on his auto, I think it's up to everyone to figure that up for themselves.

neutral coasting prolongs the coast but where I drive even If I did put it in N I would run out of space. Even when I leave it in D I have to brake because there is just too many cars. When I coast like 1/4 mile from the light then by the time I make it there it's green and I just continue. I think having an auto is stupid unless it has the manumatic feature on it.

[psyshack]

In the Accord the best coast is N ice off. Then its a draw between N coast ice on. And D coast ice on.

With ice on N coast you can bet Im ripping off a coast as if ice was off. EXCEPT I may be running the A/C. Yes I do run the A/C alot in the summer months.

With ice on in D Im light timing and have a very short coast. A/C on or off.

If Im not going to have a good light timing or something else comes up then Im ice off and stay off at the light.

I love to bust really long ice off N coast. The Accord is a coasting fool!

[mtbiker278]

I've been trying both coasting in D and coasting in N witht he engine on. So far I'm starting to believe that coasting in D saves some gas, but not much compared to N. I have the same problem as Compaq where there's really not enough room to coast effectively. I've tried engine off coasting a couple times and didn't like the feeling. The number one issue I have is the power steering cuts out. The first time I did it I freaked myself out cause I though my steering locked up or something like when you take the key out of the ignition. Thank god it was only a very small arching stop.

Until I get a scangauge or a service manual to figure out whether or not my injectors shut off I think I'm going to stick to engine off coasting.

[ketel0ne]

I read this whole posts and like some other posts, there is not really an answer to the question as to whether coasting in auto in N with the engine on and no throttle then shifting to D is bad.

I have seen where it has been stated that people do not see an increase in an auto between coasting in D or N, well I know for sure my Yaris will coast faster with it in N, on a steep downhill in D the car holds to about 60 or 65 for a long time. In N it goes upwards of 70 almost immediatly. In D I don
t have to slow down the coast at all, in N I would be doing 90 or better by the bottom of the hill (mountain).

So is the N to D no throttle safe?

[Compaq888]

Originally Posted by ketel0ne

I read this whole posts and like some other posts, there is not really an answer to the question as to whether coasting in auto in N with the engine on and no throttle then shifting to D is bad.

I have seen where it has been stated that people do not see an increase in an auto between coasting in D or N, well I know for sure my Yaris will coast faster with it in N, on a steep downhill in D the car holds to about 60 or 65 for a long time. In N it goes upwards of 70 almost immediatly. In D I don
t have to slow down the coast at all, in N I would be doing 90 or better by the bottom of the hill (mountain).

So is the N to D no throttle safe?

Depends on a lot of things. Your transmission being the primary. You can try it once. if you don't like how it acts don't do it again.

[SVOboy]

Liking how it acts has nothing to do with how safe it is.

Anyway, it's fine. Giving in throttle is what causes issue because you're putting stress on the transmission. At idle it's just slipping around like auto transmissions slip slip slip.

[Gary Palmer]

Originally Posted by ketel0ne

I read this whole posts and like some other posts, there is not really an answer to the question as to whether coasting in auto in N with the engine on and no throttle then shifting to D is bad.

I have seen where it has been stated that people do not see an increase in an auto between coasting in D or N, well I know for sure my Yaris will coast faster with it in N, on a steep downhill in D the car holds to about 60 or 65 for a long time. In N it goes upwards of 70 almost immediatly. In D I don
t have to slow down the coast at all, in N I would be doing 90 or better by the bottom of the hill (mountain).

So is the N to D no throttle safe?

On an automatic, I would strongly recommend not shifting into neutral, then shifting back to drive. Every time you shift, it requires a number of clutch's, which are small disc's really, to released and recompressed. Each time they get compressed, they get a small amount of wear. With the number in their, the wear isn't worth any gain in fuel efficiency, in my perspective.

Addititonally, in most automatic's, if something happened to cause the engine to turn off, then the automatic doesn't have any way of re-engaging, because the solenoids work off of oil pressure, which is generated by a turning pump, which runs off of the engine. If the automatic is in gear and the engine dies, then the transmission will keep the engine and the pump turning, so that you still have the load of the engine on the car, to help slow it down. If you have it in neutral and that happens, then you have no load, which is bad, bad!

[omgwtfbyobbq]

I was thinking, if the auto really does cut fuel when coasting, then breaking up driving into small P&G intervals should really help out with FE. The driver could pick a target speed, and window, so depending on how much of the time they pulse and how much they glide, pumping losses could be reduced by that ratio. I'm thinking something like a 20% increase in FE could be attained with this technique in an auto, but it really depends on whether the injectors shut off. Does anyone know how I can test this, for cheap?
I've seen the fancy induction tach the smog places uses, but is there a low tech solution that can tell me if there is a signal or not?

[SVOboy]

Hmm, just hook a light up to your injector's switched ground and if it's not flashing then the injector ain't turnin' on.