Miata List Archive

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Mail From: derek (Derek Marshall)

Interesting comments on gas mileage lately. Basically, that is not of great
concern to my use of the Miata since it is not a daily drive; however, it
definitely can be a clue as to how well the engine is working. I mull these
thoughts over as I drive. Something sticks in my mind: Someone said, at 4000
rpm the ECU goes into open loop. Suddenly I realize I don't know what this
means. What is "open loop"? I assume that fuel delivery is at a constant
pressure from the pump (what is that pressure?) and fuel variation is
controlled by the ECU as a timing factor of how long the injectors are open.
If the engine is at "open loop" at 4000 rpm, what is changing as rpm
increases to 7000 rpm? I am missing something here...if the fuel delivery is
maxed out at 4000 rpm, all I can do is deliver more air via the throttle.
Obviously something is not right with this picture. I await elucidation.

Thanks

Derek, '94 red, etc.

This read-only message was archived from a public mail list.
Mail From: pete.delmastro (pete.delmastro

Hi Derek,

In this case, Open Loop means without feedback from the 02 sensor.

Here's my understanding of how this works:

Below 4000 RPM, the engine computer uses inputs from various sensors (mass
air, throttle position, RPM) to determine how much fuel to inject (which is
controlled by fuel pressure and how long the injector is held open). The
reading from the 02 sensor is used to trim, or adjust this based on its
lean/rich indication.

Above 4000 RPM, the feedback from the 02 sensor isn't used (I'm not sure
why) and the amount of fuel is based on input of the other sensors.

I hope that helps,

-- Pete

Original Message:
-----------------
From: Derek Marshall derek at derekmarshall.com
Date: Tue, 23 Sep 2008 08:30:02 -0400
To:
Subject: [Miata] Fuel mileage


Interesting comments on gas mileage lately. Basically, that is not of great
concern to my use of the Miata since it is not a daily drive; however, it
definitely can be a clue as to how well the engine is working. I mull these
thoughts over as I drive. Something sticks in my mind: Someone said, at 4000
rpm the ECU goes into open loop. Suddenly I realize I don't know what this
means. What is "open loop"? I assume that fuel delivery is at a constant
pressure from the pump (what is that pressure?) and fuel variation is
controlled by the ECU as a timing factor of how long the injectors are open.
If the engine is at "open loop" at 4000 rpm, what is changing as rpm
increases to 7000 rpm? I am missing something here...if the fuel delivery is
maxed out at 4000 rpm, all I can do is deliver more air via the throttle.
Obviously something is not right with this picture. I await elucidation.

Thanks

Derek, '94 red, etc.

_______________________________________________
Miata mailing list
Miata at list.realbig.com
list.realbig.com/mailman/listinfo/miata

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Mail From: john.freas (John Freas)

Previously on Fuel mileage, Derek Marshall <derek at derekmarshall.com> said...

Interesting comments on gas mileage lately. Basically, that is not of great
> concern to my use of the Miata since it is not a daily drive; however, it
> definitely can be a clue as to how well the engine is working. I mull these
> thoughts over as I drive. Something sticks in my mind: Someone said, at
> 4000
> rpm the ECU goes into open loop. Suddenly I realize I don't know what this
> means. What is "open loop"? I assume that fuel delivery is at a constant
> pressure from the pump (what is that pressure?) and fuel variation is
> controlled by the ECU as a timing factor of how long the injectors are
> open.
> If the engine is at "open loop" at 4000 rpm, what is changing as rpm
> increases to 7000 rpm? I am missing something here...if the fuel delivery
> is
> maxed out at 4000 rpm, all I can do is deliver more air via the throttle.
> Obviously something is not right with this picture. I await elucidation.


Welcome to the world of emissions control.

In this world, you can make power, or you can be clean. We trade one
against the other constantly in order to make both the customer and the EPA
happy. Actually it's more complicated than that since being clean in one
area dirties up another, but I digress.

In pursuit of a happy EPA we have the catalytic converter which takes in
Non-Methane Hydrocarbons (NMHC), Oxides of Nitrogen (NOx) and Carbon
Monoxide (CO) and converts them as best it can into Carbon Dioxide, Nitrogen
and Water.

To help protect the catalytic converter (which doesn't like unburned fuel)
and ensure it can work properly, and to improve fuel economy we have the
Oxygen Sensor. The Oxygen Sensor, as its name suggests, can detect the
relative amount of oxygen in the exhaust stream and produces a variable
voltage output in response. The amount of oxygen in the exhaust stream is
an indication of how complete the combustion process is, and how rich or
lean the engine is running. Too little oxygen indicates too much fuel. Too
much oxygen indicates too little fuel. We always need some extra oxygen in
the exhaust to use in the catalytic converter. This oxygen sensor input
(Lambda) to the ECU lets the computer modify its fuel delivery in order to
optimize economy and to deliver sufficient oxygen to the catalytic converter
for it to do its job. This is called "Closed Loop Mode" where the ECU
refers to a coded fueling table to start the process, then the oxygen sensor
tells it how it worked out. If it's too rich, the ECU adjusts the fueling
downward from the base fueling that it read from the fueling table. If it
is too lean, it adds a bit of fuel, and so on, trying to get the mixture
just right.

However the oxygen sensor only works when it is heated to a certain
temperature, and can produce confusing inputs during certain events such as
motoring. In addition, there are times when the engine does not need fine
tuning in order to meet emissions regulations (at least in the NA cars), and
so in those situations the engine disregards any input from the oxygen
sensor and just delivers fuel according to the base fuel map (or a modified
map if it has the ability to learn). This is "Open Loop" mode. If the
oxygen sensor fails, the car will go into open loop all the time, however in
order to protect the engine, the base fueling map below 4,000 RPM is
deliberately set on the rich side and so you will notice reduced fuel
economy.

I have been told that the NA cars go into open loop at 4,000 RPM, and I
don't doubt the information. Based on that I conclude that the engine is
able to meet 1989-1997 emission regulations above 4,000 RPM without using a
very sharp pencil on the fueling curves. Since that is not an issue, the
car adopts a power/performance fueling curve at 4,000 RPM and follows it to
red line. That's why everyone says they can feel the car begin to pull
harder above 3,500-4,000 RPM; it just went into open loop. The EPA dropped
the reins and off we go.

For more information on emission controls, catalytic converters and oxygen
sensors, have a look at:
auto.howstuffworks.com/catalytic-converter3.htm

MiataSig -John
------------------------------
John Freas <%20john7690 at comcast.net>
1992 *YELLOW* "Sting<john.freas.home.comcast.net/pix/sting/sting.html>
"
1995 Black R Package
"Spike<geocities.com/clash_girl/Spike_Scrapbook.html>
"
Elizabethtown, Indiana
- Standard Disclaimer
<john.freas.home.comcast.net/disclaimer.html>Applies -
Team LS1,2, SP, the Gap...
I love my Miata
girl<geocities.com/clash_girl/Spike_Scrapbook.html>and my
Miata
Boys <john.freas.home.comcast.net/pix/evan_and_sean.jpg>!
"I have no idea what those dimple things on the windshield frame are for."
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Mail From: flyboy (Berck E. Nash)

On Tue, 23 Sep 2008, John Freas wrote:
> I have been told that the NA cars go into open loop at 4,000 RPM, and I
> don't doubt the information. Based on that I conclude that the engine is
> able to meet 1989-1997 emission regulations above 4,000 RPM without using a
> very sharp pencil on the fueling curves. Since that is not an issue, the
> car adopts a power/performance fueling curve at 4,000 RPM and follows it to
> red line. That's why everyone says they can feel the car begin to pull
> harder above 3,500-4,000 RPM; it just went into open loop. The EPA dropped
> the reins and off we go.

My understanding is a bit different: It goes to open loop at 4,000 RPM
primarily because the primitive ECU simply isn't fast enough to take O2
input and adjust fuel injector pulses above 4,000 RPM. I'm not sure if
that's true or not, but I think that most folks with aftermarket ECU's run
them closed loop all the way to redline. A better fuel/air mixture is not
just more efficient; it's also going to make more power than a rich
mixture. The "pull" over 4,000 rpm is simply the nature of the engine--it
makes more power at higher RPM, peaking at 6,800. It's not very good at
what it does below 4,000 rpm. The folks who whine, "I drove one of those
once, and it was horribly underpowered," were invariably shifting around
3,500 rpm and never got anywhere near the power band.

And Miatas do run plenty rich over 4,000 rpm. Decreased fuel economy over
4,000rpm is the easiest way to notice.

This read-only message was archived from a public mail list.
Mail From: derek (Derek Marshall)

Thanks again for all the thoughtful and useful information about a complex
subject. Is there an ECU upgrade for an NA, normally aspirated, that makes a
worthwhile contribution to performance? Any suggestions?
Derek

-----Original Message-----
From: Berck E. Nash [mailto:flyboy at gmail.com]
Sent: Wednesday, September 24, 2008 10:43 AM
To: John Freas
Cc: Derek Marshall; miata at realbig.com
Subject: Re: [Miata] Fuel mileage

On Tue, 23 Sep 2008, John Freas wrote:
> I have been told that the NA cars go into open loop at 4,000 RPM, <snip>

My understanding is a bit different: It goes to open loop at 4,000 RPM
primarily because the primitive ECU simply isn't fast enough to take O2
input and adjust fuel injector pulses above 4,000 RPM. I'm not sure if
that's true or not, but I think that most folks with aftermarket ECU's run
them closed loop all the way to redline. A better fuel/air mixture is not
just more efficient; it's also going to make more power than a rich mixture.
The "pull" over 4,000 rpm is simply the nature of the engine--it makes more
power at higher RPM, peaking at 6,800. It's not very good at what it does
below 4,000 rpm. The folks who whine, "I drove one of those once, and it
was horribly underpowered," were invariably shifting around 3,500 rpm and
never got anywhere near the power band.

And Miatas do run plenty rich over 4,000 rpm. Decreased fuel economy over
4,000rpm is the easiest way to notice.

This read-only message was archived from a public mail list.
Mail From: Larry (Larry Alster)

Hydra from Flying Miata. Not cheap but runs closed loop all the time. Able
to increase the power a bit but probably not worth the money for just a
stock NA engine.



Larry
?
White Knight????? 1991 Crystal White?? #99 CSP
Silver Bullet??????? 1992 Silverstone???? #17 SM2? FM I+ Turbo
Honey B???????????? 1992 Sunburst Yellow #99 SM2L? JR Supercharger
Whooosh?????????? 2004 Titanium Mazdaspeed MX-5
?
LowCountry Miata? lowcountrymiataclub.net
Masters Miata
RAGS 074

-----Original Message-----
From: miata-bounces at realbig.com [mailto:miata-bounces at realbig.com] On Behalf
Of Derek Marshall
Sent: Wednesday, September 24, 2008 2:27 PM
To: 'Berck E. Nash'; 'John Freas'
Cc: miata at realbig.com
Subject: Re: [Miata] Fuel mileage

Thanks again for all the thoughtful and useful information about a complex
subject. Is there an ECU upgrade for an NA, normally aspirated, that makes a
worthwhile contribution to performance? Any suggestions?
Derek

-----Original Message-----
From: Berck E. Nash [mailto:flyboy at gmail.com]
Sent: Wednesday, September 24, 2008 10:43 AM
To: John Freas
Cc: Derek Marshall; miata at realbig.com
Subject: Re: [Miata] Fuel mileage

On Tue, 23 Sep 2008, John Freas wrote:
> I have been told that the NA cars go into open loop at 4,000 RPM, <snip>

My understanding is a bit different: It goes to open loop at 4,000 RPM
primarily because the primitive ECU simply isn't fast enough to take O2
input and adjust fuel injector pulses above 4,000 RPM. I'm not sure if
that's true or not, but I think that most folks with aftermarket ECU's run
them closed loop all the way to redline. A better fuel/air mixture is not
just more efficient; it's also going to make more power than a rich mixture.
The "pull" over 4,000 rpm is simply the nature of the engine--it makes more
power at higher RPM, peaking at 6,800. It's not very good at what it does
below 4,000 rpm. The folks who whine, "I drove one of those once, and it
was horribly underpowered," were invariably shifting around 3,500 rpm and
never got anywhere near the power band.

And Miatas do run plenty rich over 4,000 rpm. Decreased fuel economy over
4,000rpm is the easiest way to notice.

_______________________________________________
Miata mailing list
Miata at list.realbig.com
list.realbig.com/mailman/listinfo/miata

This read-only message was archived from a public mail list.
Mail From: fallstone (Bruce MacKay)

Just bought a Link Obiwan ECU from FM. Haven't installed it yet (my son the
tech is memorizing the manual first), but Keith Tanner says that we should
notice both dramatically increased drivability as well as a modest power
increase in our naturally aspirated NA (a NA NA?).

The Obiwans were the generation before the Hydra; they're somewhat less
expensive as a result - if you can find one. We were lucky.

FM tells me that the Obiwan will control the FM II turbo quite nicely, thank
you....and buying the ECU in advance does a lot to drop the cost of the
turbo kit when that time comes.

Bruce MacKay

On Wed, Sep 24, 2008 at 2:41 PM, Larry Alster <Larry at miata.net> wrote:

> Hydra from Flying Miata. Not cheap but runs closed loop all the time.
> Able
> to increase the power a bit but probably not worth the money for just a
> stock NA engine.
>
>
>
> Larry
>
> White Knight 1991 Crystal White #99 CSP
> Silver Bullet 1992 Silverstone #17 SM2 FM I+ Turbo
> Honey B 1992 Sunburst Yellow #99 SM2L JR Supercharger
> Whooosh 2004 Titanium Mazdaspeed MX-5
>
> LowCountry Miata lowcountrymiataclub.net
> Masters Miata
> RAGS 074
>
> -----Original Message-----
> From: miata-bounces at realbig.com [mailto:miata-bounces at realbig.com] On
> Behalf
> Of Derek Marshall
> Sent: Wednesday, September 24, 2008 2:27 PM
> To: 'Berck E. Nash'; 'John Freas'
> Cc: miata at realbig.com
> Subject: Re: [Miata] Fuel mileage
>
> Thanks again for all the thoughtful and useful information about a complex
> subject. Is there an ECU upgrade for an NA, normally aspirated, that makes
> a
> worthwhile contribution to performance? Any suggestions?
> Derek
>
> -----Original Message-----
> From: Berck E. Nash [mailto:flyboy at gmail.com]
> Sent: Wednesday, September 24, 2008 10:43 AM
> To: John Freas
> Cc: Derek Marshall; miata at realbig.com
> Subject: Re: [Miata] Fuel mileage
>
> On Tue, 23 Sep 2008, John Freas wrote:
> > I have been told that the NA cars go into open loop at 4,000 RPM, <snip>
>
> My understanding is a bit different: It goes to open loop at 4,000 RPM
> primarily because the primitive ECU simply isn't fast enough to take O2
> input and adjust fuel injector pulses above 4,000 RPM. I'm not sure if
> that's true or not, but I think that most folks with aftermarket ECU's run
> them closed loop all the way to redline. A better fuel/air mixture is not
> just more efficient; it's also going to make more power than a rich
> mixture.
> The "pull" over 4,000 rpm is simply the nature of the engine--it makes more
> power at higher RPM, peaking at 6,800. It's not very good at what it does
> below 4,000 rpm. The folks who whine, "I drove one of those once, and it
> was horribly underpowered," were invariably shifting around 3,500 rpm and
> never got anywhere near the power band.
>
> And Miatas do run plenty rich over 4,000 rpm. Decreased fuel economy over
> 4,000rpm is the easiest way to notice.
>
> _______________________________________________
> Miata mailing list
> Miata at list.realbig.com
> list.realbig.com/mailman/listinfo/miata
>
> _______________________________________________
> Miata mailing list
> Miata at list.realbig.com
> list.realbig.com/mailman/listinfo/miata
>
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Mail From: dillon.boyer (Dillon)

I'm in the process of putting a Megasquirt I ECU in my stock '99, not for
performance so much as an intellectual exercise before I go turbo (at which
point I will need an aftermarket ECU).
I'm hoping that when tuned I will have improved fuel economy.

A pre-assembled Megasquirt I from diyautotune is around $300. A plug and
play kit for an NA is a bit more - check out their site.
It's less capable than a Hydra but it's also a fraction of the price.

On Wed, Sep 24, 2008 at 11:26 AM, Derek Marshall <derek at derekmarshall.com>wrote:

> Thanks again for all the thoughtful and useful information about a complex
> subject. Is there an ECU upgrade for an NA, normally aspirated, that makes
> a
> worthwhile contribution to performance? Any suggestions?
> Derek
>
> -----Original Message-----
> From: Berck E. Nash [mailto:flyboy at gmail.com]
> Sent: Wednesday, September 24, 2008 10:43 AM
> To: John Freas
> Cc: Derek Marshall; miata at realbig.com
> Subject: Re: [Miata] Fuel mileage
>
> On Tue, 23 Sep 2008, John Freas wrote:
> > I have been told that the NA cars go into open loop at 4,000 RPM, <snip>
>
> My understanding is a bit different: It goes to open loop at 4,000 RPM
> primarily because the primitive ECU simply isn't fast enough to take O2
> input and adjust fuel injector pulses above 4,000 RPM. I'm not sure if
> that's true or not, but I think that most folks with aftermarket ECU's run
> them closed loop all the way to redline. A better fuel/air mixture is not
> just more efficient; it's also going to make more power than a rich
> mixture.
> The "pull" over 4,000 rpm is simply the nature of the engine--it makes more
> power at higher RPM, peaking at 6,800. It's not very good at what it does
> below 4,000 rpm. The folks who whine, "I drove one of those once, and it
> was horribly underpowered," were invariably shifting around 3,500 rpm and
> never got anywhere near the power band.
>
> And Miatas do run plenty rich over 4,000 rpm. Decreased fuel economy over
> 4,000rpm is the easiest way to notice.
>
> _______________________________________________
> Miata mailing list
> Miata at list.realbig.com
> list.realbig.com/mailman/listinfo/miata
>
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Mail From: bryanewyatt (Bryan Wyatt)

I wasn't aware that the MS (plug and play) could deal with the return-less fuel system and VICS of the 99-00.? It definitely can't deal with VVT in 01+ cars.? Did I miss something?

-Bryan

--- On Thu, 9/25/08, Dillon <dillon.boyer at gmail.com> wrote:
From: Dillon <dillon.boyer at gmail.com>
Subject: Re: [Miata] Fuel mileage
To: "Derek Marshall" <derek at derekmarshall.com>
Cc: miata at realbig.com, "Berck E. Nash" <flyboy at gmail.com>
Date: Thursday, September 25, 2008, 12:58 AM

I'm in the process of putting a Megasquirt I ECU in my stock '99, not for performance so much as an intellectual exercise before I go turbo (at which point I will need an aftermarket ECU). ?

I'm hoping that when tuned I will have improved fuel economy. ?
A pre-assembled Megasquirt I from diyautotune is around $300. ?A plug and play kit for an NA is a bit more - check out their site.

It's less capable than a Hydra but it's also a fraction of the price.

On Wed, Sep 24, 2008 at 11:26 AM, Derek Marshall <derek at derekmarshall.com> wrote:

Thanks again for all the thoughtful and useful information about a complex

subject. Is there an ECU upgrade for an NA, normally aspirated, that makes a

worthwhile contribution to performance? Any suggestions?

Derek



-----Original Message-----

From: Berck E. Nash [mailto:flyboy at gmail.com]

Sent: Wednesday, September 24, 2008 10:43 AM

To: John Freas

Cc: Derek Marshall; miata at realbig.com

Subject: Re: [Miata] Fuel mileage



On Tue, 23 Sep 2008, John Freas wrote:

> I have been told that the NA cars go into open loop at 4,000 RPM, <snip>



My understanding is a bit different: It goes to open loop at 4,000 RPM

primarily because the primitive ECU simply isn't fast enough to take O2

input and adjust fuel injector pulses above 4,000 RPM. ?I'm not sure if

that's true or not, but I think that most folks with aftermarket ECU's run

them closed loop all the way to redline. ?A better fuel/air mixture is not

just more efficient; it's also going to make more power than a rich mixture.

The "pull" over 4,000 rpm is simply the nature of the engine--it makes more

power at higher RPM, peaking at 6,800. ?It's not very good at what it does

below 4,000 rpm. ?The folks who whine, "I drove one of those once, and it

was horribly underpowered," were invariably shifting around 3,500 rpm and

never got anywhere near the power band.



And Miatas do run plenty rich over 4,000 rpm. ?Decreased fuel economy over

4,000rpm is the easiest way to notice.



_______________________________________________

Miata mailing list

Miata at list.realbig.com

list.realbig.com/mailman/listinfo/miata



_______________________________________________
Miata mailing list
Miata at list.realbig.com
list.realbig.com/mailman/listinfo/miata




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Mail From: dillon.boyer (dillon.boyer

It's not plug and play, so I bought a harness to hack up (you could
build your own harness or hack the factory harness for cheaper if you
trust your wiring/soldering technique). I'm also letting the stock
ECU handle idle and AC control. The MS will have full control over
fuel/timing. This is a "parallel" install as opposed to a full
standalone or piggyback.

You can see my clumsy musings and project write-ups at
disassembly.dillononthecoast.com.

On 9/25/08, Bryan Wyatt <bryanewyatt at yahoo.com> wrote:
> I wasn't aware that the MS (plug and play) could deal with the return-less
> fuel system and VICS of the 99-00. It definitely can't deal with VVT in 01+
> cars. Did I miss something?
>
> -Bryan
>
> --- On Thu, 9/25/08, Dillon <dillon.boyer at gmail.com> wrote:
> From: Dillon <dillon.boyer at gmail.com>
> Subject: Re: [Miata] Fuel mileage
> To: "Derek Marshall" <derek at derekmarshall.com>
> Cc: miata at realbig.com, "Berck E. Nash" <flyboy at gmail.com>
> Date: Thursday, September 25, 2008, 12:58 AM
>
> I'm in the process of putting a Megasquirt I ECU in my stock '99, not for
> performance so much as an intellectual exercise before I go turbo (at which
> point I will need an aftermarket ECU).
>
> I'm hoping that when tuned I will have improved fuel economy.
> A pre-assembled Megasquirt I from diyautotune is around $300. A plug and
> play kit for an NA is a bit more - check out their site.
>
> It's less capable than a Hydra but it's also a fraction of the price.
>
> On Wed, Sep 24, 2008 at 11:26 AM, Derek Marshall <derek at derekmarshall.com>
> wrote:
>
> Thanks again for all the thoughtful and useful information about a complex
>
> subject. Is there an ECU upgrade for an NA, normally aspirated, that makes a
>
> worthwhile contribution to performance? Any suggestions?
>
> Derek
>
>
>
> -----Original Message-----
>
> From: Berck E. Nash [mailto:flyboy at gmail.com]
>
> Sent: Wednesday, September 24, 2008 10:43 AM
>
> To: John Freas
>
> Cc: Derek Marshall; miata at realbig.com
>
> Subject: Re: [Miata] Fuel mileage
>
>
>
> On Tue, 23 Sep 2008, John Freas wrote:
>
>> I have been told that the NA cars go into open loop at 4,000 RPM, <snip>
>
>
>
> My understanding is a bit different: It goes to open loop at 4,000 RPM
>
> primarily because the primitive ECU simply isn't fast enough to take O2
>
> input and adjust fuel injector pulses above 4,000 RPM. I'm not sure if
>
> that's true or not, but I think that most folks with aftermarket ECU's run
>
> them closed loop all the way to redline. A better fuel/air mixture is not
>
> just more efficient; it's also going to make more power than a rich mixture.
>
> The "pull" over 4,000 rpm is simply the nature of the engine--it makes more
>
> power at higher RPM, peaking at 6,800. It's not very good at what it does
>
> below 4,000 rpm. The folks who whine, "I drove one of those once, and it
>
> was horribly underpowered," were invariably shifting around 3,500 rpm and
>
> never got anywhere near the power band.
>
>
>
> And Miatas do run plenty rich over 4,000 rpm. Decreased fuel economy over
>
> 4,000rpm is the easiest way to notice.
>
>
>
> _______________________________________________
>
> Miata mailing list
>
> Miata at list.realbig.com
>
> list.realbig.com/mailman/listinfo/miata
>
>
>
> _______________________________________________
> Miata mailing list
> Miata at list.realbig.com
> list.realbig.com/mailman/listinfo/miata
>
>
>
>