Napboy

is this the same tps system that doesn't work when you switch to aftermarket wheels? if so, is it just controlled by maf readings or are there sensors elsewhere?

BlueFrenzy

Wow I learn something everyday! Thanks Rasputin. I had no such idea that going downhill would under decel would consume zero fuel.

So to add to RWagz question: To be considered deceleration, brakes have to be engaged correct? What about situations where you are going downhill in gear and have little (or none) throttle engaged? Is that still consider a DFCO?

On a side note, I remember reading here that a fellow was out of town and was no where near a gas station. His gas fuel light came on. He ended up coasting the rest of the trip (all downhill) until he reach a gas station (for close to 80km?). Mind you I can get an additional 50-60km of mileage when the light comes on.

truemagellen

think about it this way...your not giving it gas during a deceleration in gear...the computer gives itself it's own gas to keep the engine going

truemagellen

oh I guess it was already answered...well interesting thread everyone! :D

rx8wannahave

Hymee...thanks, now I know.

truemagellen

Hymee wasn't posting on this thread...

did you mean Rasputin?

Johnnyma45

Very useful info here guys. It seems everytime I click on rx8club.com I learn something new, whether it's rev matching or engine decel.

GiN

Throttle Position Sensor, not Tyre Pressure Monitoring System...

Mikelikes2drive

interesting! lets see if this actually helps my mpg...

so when im going to a red light... i should stay in lets say 6th gear until my rpms reach like... 1500 rpms and then shift to nuetral???

Sigma

It is illegal in almost every state.

You live in San Francisco, right? According to the California DMV, it is a violation to coast on a downgrade in Neutral. It's a violation of Vehicle Code 21710 and is a ticketable offense.

Why is it illegal? Because it's inherently dangerous.

Gomez

NO! The best method involves coming down through the gears, foot off the accelerator, using engine braking all the way and applying brakes at the lights. If you put it in neutral and coast, you'll inject fuel when the engine drops to idle. By being in gear and taking your foot off the pedal, your engine will not use any fuel at all. No fuel is injected when the engine is decelerating. Brakes on or off....makes no difference. This has been happening on fuel injected cars for years. My '94 Ford does this.

Gomez.

RX4life

youre a nut... :p

Rasputin

No, DFCO does not need brake activation to work.


I knew that would happen at some point. Although it's easy to differenciate us : Hymee does not have an Hymee avatar!:D

Ellar

Try not to go through life with the attitude that if you've never heard something before, it's automatically a rediculous statement.

MassiveAttack

Come, on, in Alabama it is legal to drive the wrong way down a one-way street if you have a lantern attached to the front of your automobile. Yeah, and that reduces the risk from inherently dangerous to safe?

The fact is, when doing my research on this, it seems that any state that does have a law regarding coasting in neutral specifically states that is illegal to coast on a downgrade in neutral. Is coasting uphill less inherently dangerous?

Well, yes, it is. Coasting isn't going to make you any less likely to avoid an accident (that round thing you hold on to and the middle pedal still work fine), but it could make you more likely to accelerate, thereby creating an unsafe situation. So, the risk has nothing to do with the gear your car is in or the ability to return it to gear in a timely fashion, but to prevent runaway vehicles that could potentially overheat their brakes.

Frankly, if this hill you're talking about has just enough of a downgrade to overcome rotational friction, but not enough to accelerate your car, I say go for it. Just don't tell the police what you were doing...

--Massive

cletus

On my old car with one of the instananeous gas usage readouts, I'd get roughly 40mpg coasting out of gear (in neutral) at about 40mph. If I coasted in gear, it would peg the reading out at 200+mpg. Another simple way to look at it is your accessories have to be powered somehow. Altenator, A/C, PS, these all need power. So, if you are in neutral, the engine is have to consume enough fuel to make enough power to run these. In gear, you are using gravity/kinetic energy to do this.

It's illegal here in GA too. Still not exactly sure how they could know you were to ticket you though.

DaGnome

Ok... this is a statement I'd never thought I'd hear in a technical discussion of engine performance. :D

rx8wannahave

Gosh...thanks again, I think I can hit 20mpg now that I know I was wasting gas all this time.

I'll post if I see a difference!

expo1

After watching the Robin Williams movie " The World According to Garp" I would never coast

Rasputin

Expect a 0.5% improvement at best. And if you can measure it, please let me know which fuel measurment device you use, I would become the official importer for Europe or buy out the company that makes it....

Raevik

Let's not be overdramatic. We've got some real zealots on this forum. Who cares if it's a ticketable offense....99% of us drive over the speed limit from time to time, right? Talk about hypocrisy.

I don't think the poster who brought it up was looking for a driving lesson on safety. The question was regarding fuel economy and mechanical impact of coasting, and it's been answered.

Sigma

The point wasn't that some of us do or don't do it. The point was that the poster claimed that it wasn't illegal, when it is in fact illegal in most states.

If the comment was about speeding, and someone said "Speeding isn't Illegal" I would expect someone to correct them on that as well. Whether you speed yourself or not has no bearing on the factualness of the illegality of the act. Saying "Idiot, speeding is illegal" doesn't mean nor make any implication that the person stating it doesn't speed themselves; they're only correcting an incorrect statement.

Sigma

Go to a track, accelerate very quickly, put the car in neutral, and try to make it around a particular group of sharp turns without any power to the wheels. Then do the same with the car in gear and come back with the results.

I think you'd be surprised by how much more control you have over the car when it's in gear and you can modulate the throttle than when you do not. People's reliance on "that round thing and the middle pedal" (forgetting about the other one or two pedals that are also down there) is exactly why people can't evasively drive anymore and MANY accidents occur that could easily have been prevented if people knew to do more than "stomp on middle pedal and twist wheel".

And the rhetort is going to be "If it's so dangerous to drive in Neutral, then why is it only illegal to coast while going downhill and not while driving on level ground" -- and, in some states, it is in fact illegal to coast in Neutral period, whether downhill, uphill, or level ground; meaning that it does not, in fact, have to do solely with overheating brakes.

rx8wannahave

Does fingers and a calculator count? LOL

I've been tracking my fuel economy since I got my 8 in December but I've always used the coasting method thinking that it helped fuel economy. Now that I've seen the light...I'll have to check again.

LOL...what? LOL...I know you did not say I would save a significant amount of fuel economy but .5%....it's not worth the effort...LOL

All this time I thought I would get another 1mpg out of this, LOL...but I'll try it anyway and see what happens.

MassiveAttack

Yeah, but when you're coasting on the highway or around your neighborhood or such you're not running your engine at >50% of redline RPM as you would be on the track. Modulating the throttle isn't going to help much going 50mph in 6th gear. I'm not saying you don't have more control with the ability to control the throttle, but if you're going to be coasting to "relax" the engine and fuel pump, I'd doubt that you choose to be in the appropriate gear to do any emergency acceleration, either. Heck, in that case, it would take MORE time to shift to the appropriate gear than if you had it in neutral to start with.

BTW, I don't think I'd be suprised how much more control I have over the car when it's in gear...

Yes, in some states it is illegal to coast in neutral. In some it isn't (except for the nearly universal downgrade no-coasting). In some, it's illegal to coast with the clutch disengaged, regardless of whether the transmission is in gear or in neutral. Frankly, it's pretty easy to see that these laws are targeted primarily at those driving big, heavy trucks (moving vans, semis, etc). For passenger cars, I just can't see any reasonable argument that would say that coasting in neutral is, in itself, "inherently dangerous". I think changing lanes on the highway puts lives in greater peril, but to each his own...

--Massive