Honda Car Forum

Dan C wrote:
> On Wed, 23 Jul 2008 06:00:57 -0700, jim beam wrote:
>
>>> As I understand it you are saying that during the period when
>>> 'coasting' to stop no fuel is being admitted to the engine. If this
>>> correct at some point fuel must be readmitted to allow the engine to
>>> idle when the vehicle is at stop. The question is how does the
>>> 'system' determine when fuel is to be readmitted during the coasting
>>> event to prevent the engine from 'stopping' when at rest?
>
>> the computer monitors rpm's and starts re-injecting below a base
>> threshold. older systems, that's about 1500rpm. according to tegger,
>> more modern systems cut it to as low as 750rpm.
>
> Let me get this straight. I think you are claiming that the engine uses
> *NO FUEL* during coasting...., right? So, let's think of an example....
> If I was coming down a large mountain, on the Interstate, at 65mph, and
> was to *COAST* for 20 miles (entirely realistic in some places), you are
> saying that I would not use ANY FUEL? Right?
>
> My take on that is that it's absolutely wrong. The engine is still
> running, even if it's not doing any real "work". It is using fuel.
>
>

nope. the engine is turning because it's in gear and the weight of the
vehicle is pushing it down hill. in this situation, the computer will
inject zero fuel. not one drop. [unless you put your foot on the gas
again of course.]

go to megasquirt.info, dig through until you find the source code, read
it, and there you will see an example of the shut-off, and the
parameters the computer uses to do it.

"Tomes" <ask.me@here.net> wrote in message
news:g665fl$s71$1@registered.motzarella.org...
> "Dave L" ...
>> "Tomes" ...
>>> "Dave L" ...
>>>>
>>>> I read through this thread with amusement and I believe dbu. There is
>>>> a Sunoco gas station here in Baltimore County, MD. It was on York
>>>> Road, by Seminary Avenue in an area called Lutherville. They sell
>>>> Premium at the same cost as mid grade. It used to be a Mobile station
>>>> before they changed maybe over a year ago, but apparently same owner
>>>> since they were doing this when they were a Mobile station. They have
>>>> mechanics bays and a very small convenience section.
>>>>
>>>> Why do they do this? Don't know - maybe to get people to buy gas, get
>>>> to know them and maybe have their car worked on by the mechanic? I
>>>> don't ask, but used to buy gas there in my previous car when I used
>>>> premium. Also had the car worked on by the mechanic before. He's a
>>>> decent mechanic. If you're ever in the area and want to see for
>>>> yourself, swing by. They've been doing this at least for the past 5
>>>> years. And no, I'm not going to take a picture - not worth the time,
>>>> but it is a brand name gas.
>>>>
>>>
>>> Back when I was in HS and College I worked at a Shell station in
>>> Middletown NJ. This was at the time gas was about 50 cents per gallon.
>>> Whenever we ran out of regular [and it happened many times] we were
>>> instructed to lower the price of premium down to the regular price so
>>> the customers wer not pissed off that we had none of their gas. They
>>> were always really happy about this. This was when the price was
>>> regular, 2 cent more for midgrade and 4 cent more for premium.
>>> Tomes
>>
>> Yup, I remember when the spread between regular and premium was much
>> smaller than now. When did gas stations start coming out with mid-grade?
>> I thought it was more recent than the gas being 50 cents.
>>
> Now I am trying to remember better (ouch). I think that the mid-grade was
> the unleaded right when unleaded came out, and the regular and premium
> were leaded. This was 1975-8ish.
> Tomes

Ya got me there. I can't remember what the pumps were that far back. I
wasn't even hear driving yet!

-Dave

On 2008-07-23, Dan C <youmustbejoking@lan.invalid> wrote:
> On Wed, 23 Jul 2008 06:00:57 -0700, jim beam wrote:
>
>>> As I understand it you are saying that during the period when
>>> 'coasting' to stop no fuel is being admitted to the engine. If this
>>> correct at some point fuel must be readmitted to allow the engine to
>>> idle when the vehicle is at stop. The question is how does the
>>> 'system' determine when fuel is to be readmitted during the coasting
>>> event to prevent the engine from 'stopping' when at rest?
>
>> the computer monitors rpm's and starts re-injecting below a base
>> threshold. older systems, that's about 1500rpm. according to tegger,
>> more modern systems cut it to as low as 750rpm.
>
> Let me get this straight. I think you are claiming that the engine uses
> *NO FUEL* during coasting...., right? So, let's think of an example....
> If I was coming down a large mountain, on the Interstate, at 65mph, and
> was to *COAST* for 20 miles (entirely realistic in some places), you are
> saying that I would not use ANY FUEL? Right?
>
> My take on that is that it's absolutely wrong. The engine is still
> running, even if it's not doing any real "work". It is using fuel.

Your take on that is completely wrong. In this case, the engine is
being driven by the transmission. No combustion is taking place. The
engine runs on the energy of the downhill glide until your RPM's get
low enough that the fuel needs to be injected again to keep the engine
running.


--
Joe - Linux User #449481/Ubuntu User #19733
joe at hits - buffalo dot com
"Hate is baggage, life is too short to go around pissed off all the
time..." - Danny, American History X

On Wed, 23 Jul 2008 18:43:20 -0500, Joe wrote:

> On 2008-07-23, Dan C <youmustbejoking@lan.invalid> wrote:
>> On Wed, 23 Jul 2008 06:00:57 -0700, jim beam wrote:
>>
>>>> As I understand it you are saying that during the period when
>>>> 'coasting' to stop no fuel is being admitted to the engine. If this
>>>> correct at some point fuel must be readmitted to allow the engine to
>>>> idle when the vehicle is at stop. The question is how does the
>>>> 'system' determine when fuel is to be readmitted during the coasting
>>>> event to prevent the engine from 'stopping' when at rest?
>>
>>> the computer monitors rpm's and starts re-injecting below a base
>>> threshold. older systems, that's about 1500rpm. according to tegger,
>>> more modern systems cut it to as low as 750rpm.
>>
>> Let me get this straight. I think you are claiming that the engine uses
>> *NO FUEL* during coasting...., right? So, let's think of an example....
>> If I was coming down a large mountain, on the Interstate, at 65mph, and
>> was to *COAST* for 20 miles (entirely realistic in some places), you are
>> saying that I would not use ANY FUEL? Right?
>>
>> My take on that is that it's absolutely wrong. The engine is still
>> running, even if it's not doing any real "work". It is using fuel.
>
> Your take on that is completely wrong. In this case, the engine is
> being driven by the transmission. No combustion is taking place. The
> engine runs on the energy of the downhill glide until your RPM's get
> low enough that the fuel needs to be injected again to keep the engine
> running.

OK. Makes sense I guess.


--
"Ubuntu" -- an African word, meaning "Slackware is too hard for me".
The Usenet Improvement Project: http://improve-usenet.org

On Wed, 23 Jul 2008 06:00:57 -0700, jim beam
<spamvortex@bad.example.net> wrote:

snip
>
>
>>
>> Incidentally rpm and throttle position does not indicate torque
>> reversal (coasting) as you have implied.
>
>then you need to think this situation through one more time - there's no
>situation under which you can have high rpm's and a closed throttle
>unless you're coasting.


I agree I am nit picking now but a closed throttle and high rpm (plus
750-1500 rpm I think you said) is not quite the same as torque
reversal although it is certainly indicative.

This, for me, has been a very intertesting exchange and I thank you
for you explanations and patience.

Todd H. wrote:
> I mean could they make the decision any more freakin difficult...

Toyota Sienna LE 7 passenger
What did it for me was AWD, 266 HP and 245 lb.ft. of torque @ 21/30 MPG...

a

Edward W. Thompson wrote:
> On Wed, 23 Jul 2008 06:00:57 -0700, jim beam
> <spamvortex@bad.example.net> wrote:
>
> snip
>>
>>> Incidentally rpm and throttle position does not indicate torque
>>> reversal (coasting) as you have implied.
>> then you need to think this situation through one more time - there's no
>> situation under which you can have high rpm's and a closed throttle
>> unless you're coasting.
>
>
> I agree I am nit picking now but a closed throttle and high rpm (plus
> 750-1500 rpm I think you said) is not quite the same as torque
> reversal although it is certainly indicative.
>
> This, for me, has been a very intertesting exchange and I thank you
> for you explanations and patience.

The point is that the ecu doesn't *need* to detect "torque reversal" to
know when to shut off fuel. All it needs is RPM and throttle position.

a

Dan C wrote:
> On Wed, 23 Jul 2008 06:00:57 -0700, jim beam wrote:
>
>>> As I understand it you are saying that during the period when
>>> 'coasting' to stop no fuel is being admitted to the engine. If this
>>> correct at some point fuel must be readmitted to allow the engine to
>>> idle when the vehicle is at stop. The question is how does the
>>> 'system' determine when fuel is to be readmitted during the coasting
>>> event to prevent the engine from 'stopping' when at rest?
>
>> the computer monitors rpm's and starts re-injecting below a base
>> threshold. older systems, that's about 1500rpm. according to tegger,
>> more modern systems cut it to as low as 750rpm.
>
> Let me get this straight. I think you are claiming that the engine uses
> *NO FUEL* during coasting...., right? So, let's think of an example....
> If I was coming down a large mountain, on the Interstate, at 65mph, and
> was to *COAST* for 20 miles (entirely realistic in some places), you are
> saying that I would not use ANY FUEL? Right?
>
> My take on that is that it's absolutely wrong. The engine is still
> running, even if it's not doing any real "work". It is using fuel.
>
>


Not at all. think about it - take the engine out of the car and put a
handle on the crank - you can turn it with your own hand! Why is it hard
to believe that thousands of lbs. of moving car can't do that? The
friction of moving turning the engine without fuel is what slows you down
when gearing down. It's often good practise to be in a lower gear and off
the throttle when descending a steep hill - the engine resistance will slow
you or keep you at a constant speed. If there were fuel being fed to the
engine to "keep it running" then there would be no braking effect.

NB: I know this is the case with a manual transmission, but IIRC, there are
instances where an automatic still feeds a tiny amount of fuel during
"rundown".

a