"Caroline" <caroline10027remove@earthlink.net> wrote in
news62Ic.1179$sV2.224@newsread2.news.atl.earthli nk.net:

> "Jim Yanik" wrote
> "Lattes" wrote
>>> http://cgi.ebay.com/ebaymotors/ws/eB...m&rd=1&item=79
>>> 09
>> > 446934&category=33656
>>
>> I would not waste my money on this.
>> It's a device(resistor) to alter the O2 sensor's input to the ECU to
>> give "more performance".
>
> The URL above does not work.
>
> Are you referring to either of the other two URLs that the original
> poster (Lattes) gave? Namely:
>
> http://tinyurl.com/2vy2r which says, among other things, "This is a
> resistor that will plug into your AIT (air intake temp) sensor and
> modify your AIR/Fuel ratio and slightly change your engine timing to
> run stronger and with increased power."
>
> http://tinyurl.com/2bt6f a.k.a. an "intake twister."
>
> If you're referring to the device at Ebay auction site
> http://tinyurl.com/2vy2r , then this device modifies the air intake
> temperature output signal to the ECU. This signal causes the ECU to
> modify the fuel injector basic discharge duration. See
> http://tinyurl.com/22d46 for more info.
>
> The AIT sensor signal with the ECU comprises an open loop. That is,
> air intake temperature changes, the AIT sensor signal changes, and the
> ECU reads the changed AIT sensor signal. The ECU then commands a
> different fuel injector discharge. There's no feedback to tell the ECU
> whether it correctly adjusted the fuel injector discharge in response
> to the changed AIT.
>
>
>

Wouldn't the (OBD-II,since OBD-I has no AIT,AFAIK)primary O2 sensor loop
RE-correct the fuel input to maintain proper mixture,nullifying the AIT
correction?

IOW;the AIT mod changes(adds fuel?) the fuel input,enriching the
mixture,the O2 sensor detects the rich condition,and leans it out by
reducing the fuel input.(to get more power,one has to have more fuel-AIR
mixture,not just more fuel)

Colder,denser air is effectively more air,thus enabling the addition of
more fuel.That;s why cold air intakes give more power,they effectively
increase the amount of fuel-AIR charge to the cylinders.
Fooling the ECU into thinking the air is more dense(colder=more dense)when
it is truly not would only screw up the mixture,making it less optimum.

I suspect the AIT input is for when the engine has not warmed up to
operating temp,when it operates from the pre-programmed map.
--
Jim Yanik
jyanik-at-kua.net

 

"Jim Yanik" <jyanik@abuse.gov> wrote
> "Caroline" <caroline10027remove@earthlink.net> wrote
> > "Jim Yanik" wrote
> > "Lattes" wrote
> >>> http://cgi.ebay.com/ebaymotors/ws/eB...m&rd=1&item=79
> >>> 09
> >> > 446934&category=33656
> >>
> >> I would not waste my money on this.
> >> It's a device(resistor) to alter the O2 sensor's input to the ECU to
> >> give "more performance".
> >
> > The URL above does not work.
> >
> > Are you referring to either of the other two URLs that the original
> > poster (Lattes) gave? Namely:
> >
> > http://tinyurl.com/2vy2r which says, among other things, "This is a
> > resistor that will plug into your AIT (air intake temp) sensor and
> > modify your AIR/Fuel ratio and slightly change your engine timing to
> > run stronger and with increased power."
> >
> > http://tinyurl.com/2bt6f a.k.a. an "intake twister."
> >
> > If you're referring to the device at Ebay auction site
> > http://tinyurl.com/2vy2r , then this device modifies the air intake
> > temperature output signal to the ECU. This signal causes the ECU to
> > modify the fuel injector basic discharge duration. See
> > http://tinyurl.com/22d46 for more info.
> >
> > The AIT sensor signal with the ECU comprises an open loop. That is,
> > air intake temperature changes, the AIT sensor signal changes, and the
> > ECU reads the changed AIT sensor signal. The ECU then commands a
> > different fuel injector discharge. There's no feedback to tell the ECU
> > whether it correctly adjusted the fuel injector discharge in response
> > to the changed AIT.
>
> Wouldn't the (OBD-II,since OBD-I has no AIT,AFAIK)primary O2 sensor loop
> RE-correct the fuel input to maintain proper mixture,nullifying the AIT
> correction?

First, I thought OBD-II was not required until car model year 1996. So my
Chilton's manual for 1984-1995 Civics must be focusingon OBD I emissions
controls. Chilton's indicates that 1988-1995 Civics have an AIT sensor. The
Autozone site at http://tinyurl.com/22d46 suggests the same. Also,
http://www.honda.co.uk/owner/ConcertoManual/index.html indicates the 1991
Concerto (whose engine I believe is identical to the 199 Civic's engine) has an
AIT sensor.

Second, I agree that the O2 sensor kicks in at some point (e.g. after the car
has warmed up and is moving at stead speed) and also modifies the fuel injector
basic discharge duration.

I think "RE-correct" is the correct word here, but "nullify" is not. That is,
suppose the air intake temperature changes. From my reading, the ECU will
respond, and adjust accordingly, the fuel injector basic discharge duration.
Then the O2 sensor reads from the exhaust whatever oxygen content results from
(1) the new air intake temperature and (2) any new discharge duration. The O2
sensor sends its signal reflecting this. This signal doesn't eliminate or
diminish in any way the AIT signal (or any ECU correction response from this
signal), but it may cause further correction of the fuel injector basic
duration.

Two sentences from Chilton's (and Autozone at http://tinyurl.com/22d46 ) keep
leaping out at me:
____
ELECTRONIC CONTROL UNIT (ECU) [for 1991 Civics, among others]
The unit contains memories for the basic discharge duration at various engine
speeds and manifold pressures. The basic discharge duration, after being read
out from the memory, is further modified by signals sent from various sensors to
obtain the final discharge duration.
____

http://www.honda.co.uk/owner/CivicManual/pdf/11-20.pdf has the exact same words
(from "contains" on) for 1995-1997 Civics.

> IOW;the AIT mod changes(adds fuel?) the fuel input,enriching the
> mixture,the O2 sensor detects the rich condition,and leans it out by
> reducing the fuel input.(to get more power,one has to have more fuel-AIR
> mixture,not just more fuel)

My impression is it's a balancing act.

As you're probably aware, control systems like the PGM-FI system are difficult
to characterize in "step-by-step" fashion. ECU's don't respond slowly and to a
single input at any instant. ECUs are reading input from several sensors at any
time.

From my reading on Civics, I do agree only one input is also feedback (in the
closed-loop sense): The oxygen sensor's.

> Colder,denser air is effectively more air,thus enabling the addition of
> more fuel.That;s why cold air intakes give more power,they effectively
> increase the amount of fuel-AIR charge to the cylinders.

I agree the AIT sensor signal most likely reflects this.

I'm hesitating a little because there are practical limits as to how cold the
air can be before one has to worry about whether the air-fuel mixture will even
ignite. The colder the air is, the harder it is to ignite, in general. So, yes,
colder air is denser, permitting more fuel to be packed in with it, but only up
until ignition problems enter the picture.

> Fooling the ECU into thinking the air is more dense(colder=more dense)when
> it is truly not would only screw up the mixture,making it less optimum.

I agree.

I don't know what the overall effect of this Ebay auction device for the AIT
sensor is, but I'd sure be concerned it will screw up something in the car.
Perhaps first the catalytic converter, as I understand (that's the car repair
novice in me speaking) it is vulnerable to "too rich" operating conditions.

> I suspect the AIT input is for when the engine has not warmed up to
> operating temp,when it operates from the pre-programmed map.

I think the AIT input is used all the time, but in general and practically
speaking, when the car is warmed up and cruising at steady speed, any ECU
changes to fuel injector duration are mostly (but not exclusively) due to the O2
sensor.

For example, suppose a person is driving down a Colorado Rockies mountain, and
the air temperature changes markedly. It seems to me the AIT will change the
ECU fuel injector signal, but only in "gross" fashion. That is, the AIT signal
is X at the top of the mountain (50 degrees F) and Y at the bottom of the
mountain (65 degrees F). Once the car is at the bottom and stays at this lower
elevation, where the temperature is pretty steady at about 65 degrees F, the AIT
sensor signal does not change.

Is the car flip-flopping between open loop (no O2 sensor signal) and closed loop
(O2 sensor signal) while driving down such a mountain? I think so, but this
might vary from one make's ECU design to another's. All I can say with
confidence and from my reading is that, in general, when the car is warmed up
and running at steady speed, the car is in closed loop; the oxygen sensor's
signal dominates the ECU's decision-making. But the second someone hits the
accelerator or brake, all bets are off. The car may revert to open loop, by
design.

The only really clear, specific documentation I have for this is Chilton's, the
Autozone site, and the UK manual site. Otherwise, I'm drawing on a lot of
textbook control systems design experience.

 

"Caroline" <caroline10027remove@earthlink.net> wrote in
news:aSgIc.1926$sV2.339@newsread2.news.atl.earthli nk.net:

> "Jim Yanik" <jyanik@abuse.gov> wrote
>> "Caroline" <caroline10027remove@earthlink.net> wrote
>> > "Jim Yanik" wrote
>> > "Lattes" wrote
>> >>> http://cgi.ebay.com/ebaymotors/ws/eB...Item&rd=1&item
>> >>> =79 09
>> >> > 446934&category=33656
>> >>
>> >> I would not waste my money on this.
>> >> It's a device(resistor) to alter the O2 sensor's input to the ECU
>> >> to give "more performance".
>> >
>> > The URL above does not work.
>> >
>> > Are you referring to either of the other two URLs that the original
>> > poster (Lattes) gave? Namely:
>> >
>> > http://tinyurl.com/2vy2r which says, among other things, "This is a
>> > resistor that will plug into your AIT (air intake temp) sensor and
>> > modify your AIR/Fuel ratio and slightly change your engine timing
>> > to run stronger and with increased power."
>> >
>> > http://tinyurl.com/2bt6f a.k.a. an "intake twister."
>> >
>> > If you're referring to the device at Ebay auction site
>> > http://tinyurl.com/2vy2r , then this device modifies the air intake
>> > temperature output signal to the ECU. This signal causes the ECU to
>> > modify the fuel injector basic discharge duration. See
>> > http://tinyurl.com/22d46 for more info.
>> >
>> > The AIT sensor signal with the ECU comprises an open loop. That is,
>> > air intake temperature changes, the AIT sensor signal changes, and
>> > the ECU reads the changed AIT sensor signal. The ECU then commands
>> > a different fuel injector discharge. There's no feedback to tell
>> > the ECU whether it correctly adjusted the fuel injector discharge
>> > in response to the changed AIT.
> >
>> Wouldn't the (OBD-II,since OBD-I has no AIT,AFAIK)primary O2 sensor
>> loop RE-correct the fuel input to maintain proper mixture,nullifying
>> the AIT correction?
>
> First, I thought OBD-II was not required until car model year 1996. So
> my Chilton's manual for 1984-1995 Civics must be focusingon OBD I
> emissions controls. Chilton's indicates that 1988-1995 Civics have an
> AIT sensor. The Autozone site at http://tinyurl.com/22d46 suggests the
> same. Also, http://www.honda.co.uk/owner/ConcertoManual/index.html
> indicates the 1991 Concerto (whose engine I believe is identical to
> the 199 Civic's engine) has an AIT sensor.

My mistake;I had thought my GSR lacked the AIT(IAT in the Haynes manual)
>
> Second, I agree that the O2 sensor kicks in at some point (e.g. after
> the car has warmed up and is moving at stead speed) and also modifies
> the fuel injector basic discharge duration.
>
> I think "RE-correct" is the correct word here, but "nullify" is not.
> That is, suppose the air intake temperature changes. From my reading,
> the ECU will respond, and adjust accordingly, the fuel injector basic
> discharge duration. Then the O2 sensor reads from the exhaust whatever
> oxygen content results from (1) the new air intake temperature and (2)
> any new discharge duration. The O2 sensor sends its signal reflecting
> this. This signal doesn't eliminate or diminish in any way the AIT
> signal (or any ECU correction response from this signal), but it may
> cause further correction of the fuel injector basic duration.
>
> Two sentences from Chilton's (and Autozone at http://tinyurl.com/22d46
> ) keep leaping out at me:
> ____
> ELECTRONIC CONTROL UNIT (ECU) [for 1991 Civics, among others]
> The unit contains memories for the basic discharge duration at various
> engine speeds and manifold pressures. The basic discharge duration,
> after being read out from the memory, is further modified by signals
> sent from various sensors to obtain the final discharge duration.
> ____
>
> http://www.honda.co.uk/owner/CivicManual/pdf/11-20.pdf has the exact
> same words (from "contains" on) for 1995-1997 Civics.
>
>> IOW;the AIT mod changes(adds fuel?) the fuel input,enriching the
>> mixture,the O2 sensor detects the rich condition,and leans it out by
>> reducing the fuel input.(to get more power,one has to have more
>> fuel-AIR mixture,not just more fuel)
>
> My impression is it's a balancing act.
>
> As you're probably aware, control systems like the PGM-FI system are
> difficult to characterize in "step-by-step" fashion. ECU's don't
> respond slowly and to a single input at any instant. ECUs are reading
> input from several sensors at any time.
>
> From my reading on Civics, I do agree only one input is also feedback
> (in the closed-loop sense): The oxygen sensor's.
>
>> Colder,denser air is effectively more air,thus enabling the addition
>> of more fuel.That;s why cold air intakes give more power,they
>> effectively increase the amount of fuel-AIR charge to the cylinders.
>
> I agree the AIT sensor signal most likely reflects this.
>
> I'm hesitating a little because there are practical limits as to how
> cold the air can be before one has to worry about whether the air-fuel
> mixture will even ignite. The colder the air is, the harder it is to
> ignite, in general. So, yes, colder air is denser, permitting more
> fuel to be packed in with it, but only up until ignition problems
> enter the picture.

I believe too cold of an air temp prevents proper atomization of the fuel
charge,thus more difficult ignition.
>
>> Fooling the ECU into thinking the air is more dense(colder=more
>> dense)when it is truly not would only screw up the mixture,making it
>> less optimum.
>
> I agree.
>
> I don't know what the overall effect of this Ebay auction device for
> the AIT sensor is, but I'd sure be concerned it will screw up
> something in the car. Perhaps first the catalytic converter, as I
> understand (that's the car repair novice in me speaking) it is
> vulnerable to "too rich" operating conditions.
>
>> I suspect the AIT input is for when the engine has not warmed up to
>> operating temp,when it operates from the pre-programmed map.
>
> I think the AIT input is used all the time, but in general and
> practically speaking, when the car is warmed up and cruising at steady
> speed, any ECU changes to fuel injector duration are mostly (but not
> exclusively) due to the O2 sensor.
>
> For example, suppose a person is driving down a Colorado Rockies
> mountain, and the air temperature changes markedly. It seems to me the
> AIT will change the ECU fuel injector signal, but only in "gross"
> fashion. That is, the AIT signal is X at the top of the mountain (50
> degrees F) and Y at the bottom of the mountain (65 degrees F). Once
> the car is at the bottom and stays at this lower elevation, where the
> temperature is pretty steady at about 65 degrees F, the AIT sensor
> signal does not change.

Perhaps the AIT input is to get the mix into an approximate range,where the
O2 sensor can fine-tune the mix for optimum? I think once the car warms
up,the under-hood temps will swamp out such air temp changes when driving
thru differing climes.The AIT would only be useful if a REALLY drastic temp
change occurred.

>
> Is the car flip-flopping between open loop (no O2 sensor signal) and
> closed loop (O2 sensor signal) while driving down such a mountain? I
> think so, but this might vary from one make's ECU design to another's.
> All I can say with confidence and from my reading is that, in general,
> when the car is warmed up and running at steady speed, the car is in
> closed loop; the oxygen sensor's signal dominates the ECU's
> decision-making. But the second someone hits the accelerator or brake,
> all bets are off. The car may revert to open loop, by design.
>
> The only really clear, specific documentation I have for this is
> Chilton's, the Autozone site, and the UK manual site. Otherwise, I'm
> drawing on a lot of textbook control systems design experience.
>
>
>

Apologies for not editing down this replay,but I wanted to retain the whole
thing for clarity.

--
Jim Yanik
jyanik-at-kua.net

 

"Jim Yanik" <jyanik@abuse.gov> wrote
> Perhaps the AIT [air intake temperature] input is to get
> the mix into an approximate range,where the O2 sensor
> can fine-tune the mix for optimum?

From my reading of the manuals, I think this is as good a way as any to put it.

> I think once the car warms
> up,the under-hood temps will swamp out such air temp changes when driving
> thru differing climes.The AIT would only be useful if a REALLY drastic temp
> change occurred.

I think you're probably right.

 

Jim Yanik wrote:
> "Caroline" <caroline10027remove@earthlink.net> wrote in
> news:aSgIc.1926$sV2.339@newsread2.news.atl.earthli nk.net:
>
>
>>"Jim Yanik" <jyanik@abuse.gov> wrote
>>
>>>"Caroline" <caroline10027remove@earthlink.net> wrote
>>>
>>>>"Jim Yanik" wrote
>>>>"Lattes" wrote
>>>>
>>>>>>http://cgi.ebay.com/ebaymotors/ws/eB...Item&rd=1&item
>>>>>>=79 09
>>>>>>446934&category=33656
>>>>>
>>>>>I would not waste my money on this.
>>>>>It's a device(resistor) to alter the O2 sensor's input to the ECU
>>>>>to give "more performance".
>>>>
>>>>The URL above does not work.
>>>>
>>>>Are you referring to either of the other two URLs that the original
>>>>poster (Lattes) gave? Namely:
>>>>
>>>>http://tinyurl.com/2vy2r which says, among other things, "This is a
>>>>resistor that will plug into your AIT (air intake temp) sensor and
>>>>modify your AIR/Fuel ratio and slightly change your engine timing
>>>>to run stronger and with increased power."
>>>>
>>>>http://tinyurl.com/2bt6f a.k.a. an "intake twister."
>>>>
>>>>If you're referring to the device at Ebay auction site
>>>>http://tinyurl.com/2vy2r , then this device modifies the air intake
>>>>temperature output signal to the ECU. This signal causes the ECU to
>>>>modify the fuel injector basic discharge duration. See
>>>>http://tinyurl.com/22d46 for more info.
>>>>
>>>>The AIT sensor signal with the ECU comprises an open loop. That is,
>>>>air intake temperature changes, the AIT sensor signal changes, and
>>>>the ECU reads the changed AIT sensor signal. The ECU then commands
>>>>a different fuel injector discharge. There's no feedback to tell
>>>>the ECU whether it correctly adjusted the fuel injector discharge
>>>>in response to the changed AIT.
>>>
>>>Wouldn't the (OBD-II,since OBD-I has no AIT,AFAIK)primary O2 sensor
>>>loop RE-correct the fuel input to maintain proper mixture,nullifying
>>>the AIT correction?
>>
>>First, I thought OBD-II was not required until car model year 1996. So
>>my Chilton's manual for 1984-1995 Civics must be focusingon OBD I
>>emissions controls. Chilton's indicates that 1988-1995 Civics have an
>>AIT sensor. The Autozone site at http://tinyurl.com/22d46 suggests the
>>same. Also, http://www.honda.co.uk/owner/ConcertoManual/index.html
>>indicates the 1991 Concerto (whose engine I believe is identical to
>>the 199 Civic's engine) has an AIT sensor.
>
>
> My mistake;I had thought my GSR lacked the AIT(IAT in the Haynes manual)
>
>>Second, I agree that the O2 sensor kicks in at some point (e.g. after
>>the car has warmed up and is moving at stead speed) and also modifies
>>the fuel injector basic discharge duration.
>>
>>I think "RE-correct" is the correct word here, but "nullify" is not.
>>That is, suppose the air intake temperature changes. From my reading,
>>the ECU will respond, and adjust accordingly, the fuel injector basic
>>discharge duration. Then the O2 sensor reads from the exhaust whatever
>>oxygen content results from (1) the new air intake temperature and (2)
>>any new discharge duration. The O2 sensor sends its signal reflecting
>>this. This signal doesn't eliminate or diminish in any way the AIT
>>signal (or any ECU correction response from this signal), but it may
>>cause further correction of the fuel injector basic duration.
>>
>>Two sentences from Chilton's (and Autozone at http://tinyurl.com/22d46
>>) keep leaping out at me:
>>____
>>ELECTRONIC CONTROL UNIT (ECU) [for 1991 Civics, among others]
>>The unit contains memories for the basic discharge duration at various
>>engine speeds and manifold pressures. The basic discharge duration,
>>after being read out from the memory, is further modified by signals
>>sent from various sensors to obtain the final discharge duration.
>>____
>>
>>http://www.honda.co.uk/owner/CivicManual/pdf/11-20.pdf has the exact
>>same words (from "contains" on) for 1995-1997 Civics.
>>
>>
>>>IOW;the AIT mod changes(adds fuel?) the fuel input,enriching the
>>>mixture,the O2 sensor detects the rich condition,and leans it out by
>>>reducing the fuel input.(to get more power,one has to have more
>>>fuel-AIR mixture,not just more fuel)
>>
>>My impression is it's a balancing act.
>>
>>As you're probably aware, control systems like the PGM-FI system are
>>difficult to characterize in "step-by-step" fashion. ECU's don't
>>respond slowly and to a single input at any instant. ECUs are reading
>>input from several sensors at any time.
>>
>>From my reading on Civics, I do agree only one input is also feedback
>>(in the closed-loop sense): The oxygen sensor's.
>>
>>
>>>Colder,denser air is effectively more air,thus enabling the addition
>>>of more fuel.That;s why cold air intakes give more power,they
>>>effectively increase the amount of fuel-AIR charge to the cylinders.
>>
>>I agree the AIT sensor signal most likely reflects this.
>>
>>I'm hesitating a little because there are practical limits as to how
>>cold the air can be before one has to worry about whether the air-fuel
>>mixture will even ignite. The colder the air is, the harder it is to
>>ignite, in general. So, yes, colder air is denser, permitting more
>>fuel to be packed in with it, but only up until ignition problems
>>enter the picture.
>
>
> I believe too cold of an air temp prevents proper atomization of the fuel
> charge,thus more difficult ignition.

shouldn't really be an issue. most modern production cars inject onto
inlet valves that are designed to run hotter than in the old days.
liquid gas on hot metal = very good evaporation!

in addition, the compression stroke raises the temperature of the
fuel/air charge very effectively. i can't recall the numbers now, but
remember, diesels work on the principle of the compressed air being hot
enough to ignite the fuel instantly it's injected. compression in a
gasoline engine is not as highas a diesel so compression temperature
rise is less, but the same principles apply.

"difficult" ignition happens when there is something like an injector
problem where droplets of fuel are entering the cylinder that are too
large to evaporate quickly enough. /that/ causes all kinds of nastiness.

>
>>>Fooling the ECU into thinking the air is more dense(colder=more
>>>dense)when it is truly not would only screw up the mixture,making it
>>>less optimum.
>>
>>I agree.
>>
>>I don't know what the overall effect of this Ebay auction device for
>>the AIT sensor is, but I'd sure be concerned it will screw up
>>something in the car. Perhaps first the catalytic converter, as I
>>understand (that's the car repair novice in me speaking) it is
>>vulnerable to "too rich" operating conditions.
>>
>>
>>>I suspect the AIT input is for when the engine has not warmed up to
>>>operating temp,when it operates from the pre-programmed map.
>>
>>I think the AIT input is used all the time, but in general and
>>practically speaking, when the car is warmed up and cruising at steady
>>speed, any ECU changes to fuel injector duration are mostly (but not
>>exclusively) due to the O2 sensor.
>>
>>For example, suppose a person is driving down a Colorado Rockies
>>mountain, and the air temperature changes markedly. It seems to me the
>>AIT will change the ECU fuel injector signal, but only in "gross"
>>fashion. That is, the AIT signal is X at the top of the mountain (50
>>degrees F) and Y at the bottom of the mountain (65 degrees F). Once
>>the car is at the bottom and stays at this lower elevation, where the
>>temperature is pretty steady at about 65 degrees F, the AIT sensor
>>signal does not change.
>
>
> Perhaps the AIT input is to get the mix into an approximate range,where the
> O2 sensor can fine-tune the mix for optimum? I think once the car warms
> up,the under-hood temps will swamp out such air temp changes when driving
> thru differing climes.The AIT would only be useful if a REALLY drastic temp
> change occurred.

afaik, air temp is monitored all the time. depends on the system i
guess because as you say, some seem only to respond to gross changes,
but in theory, air temp /should/ be monitored all the time - it affects
air density and density affects the amount of fuel that needs to be
injected.

>
>
>>Is the car flip-flopping between open loop (no O2 sensor signal) and
>>closed loop (O2 sensor signal) while driving down such a mountain? I
>>think so, but this might vary from one make's ECU design to another's.
>>All I can say with confidence and from my reading is that, in general,
>>when the car is warmed up and running at steady speed, the car is in
>>closed loop; the oxygen sensor's signal dominates the ECU's
>>decision-making. But the second someone hits the accelerator or brake,
>>all bets are off. The car may revert to open loop, by design.
>>
>>The only really clear, specific documentation I have for this is
>>Chilton's, the Autozone site, and the UK manual site. Otherwise, I'm
>>drawing on a lot of textbook control systems design experience.
>>
>>
>>
>
>
> Apologies for not editing down this replay,but I wanted to retain the whole
> thing for clarity.
>

http://www.amazon.com/exec/obidos/AS...620766-9100633

is a great book on all kinds of stuff like this.

 

jim beam <nospam@example.net> wrote in
news:bMydnbak9eLzXmzd4p2dnA@comcast.com:

> Jim Yanik wrote:


>>
>> Perhaps the AIT input is to get the mix into an approximate
>> range,where the O2 sensor can fine-tune the mix for optimum? I think
>> once the car warms up,the under-hood temps will swamp out such air
>> temp changes when driving thru differing climes.The AIT would only be
>> useful if a REALLY drastic temp change occurred.
>
> afaik, air temp is monitored all the time. depends on the system i
> guess because as you say, some seem only to respond to gross changes,
> but in theory, air temp /should/ be monitored all the time - it
> affects air density and density affects the amount of fuel that needs
> to be injected.

Except that the O2 sensor would be the final determiner of how much fuel
gets added.


--
Jim Yanik
jyanik-at-kua.net

 

IMHO, the main effect of air temp sensor modifications like this is
not on air/fuel ratio but rather on ignition timing. When the intake
air is cold, the engine is less likely to "knock" (or "ping",
"detonate", whatever you like to call it). Therefore you can use more
ignition advance, which would normally provide more power. (As a
general rule, on most engines, the ignition timing is set somewhat
retarded from optimum because of the danger of knocking).

So, if you fit a device like this that fools the engine into thinking
the air is very cold, it will apply more ignition advance which will
probably produce more power. But, it gives a very much greater risk of
catastrophic knock, which can effectively destroy the engine! Normally
there is a certain amount of safety reserve built in and so generally
you would get away with it, but things like this give me the *******,
they really do.

When the engine is cold, a false low AIT reading will probably delay
closed-loop AFR control and the engine will run slightly richer. But
the engine will enter closed-loop sooner or later and return to lambda
= 1 at part load, regardless of the outside air temp. At full load the
engine will generally be set to run at optimum lambda anyway
(typically 0.9) and adding any extra fuel is unlikely to be of
significant benefit.

As far as the air swirler thing is concerned, you may like to visit
http://homepage.ntlworld.com/cains1/...turbulence.htm for
advice on why not to bother with them!

Tony

(replace "nospam" with "fuel" to reply)

 

"Tony Cains" <nospam@tjcains.freeserve.co.uk> wrote
> IMHO, the main effect of air temp sensor modifications like this is
> not on air/fuel ratio but rather on ignition timing. When the intake
> air is cold, the engine is less likely to "knock" (or "ping",
> "detonate", whatever you like to call it). Therefore you can use more
> ignition advance, which would normally provide more power. (As a
> general rule, on most engines, the ignition timing is set somewhat
> retarded from optimum because of the danger of knocking).
>
> So, if you fit a device like this that fools the engine into thinking
> the air is very cold, it will apply more ignition advance which will
> probably produce more power.

Your theory sounds good enough, re wanting to change the timing at cooler engine
temperatures, but from the manuals the actual engine control design does not
appear to work quite this way.

For circa 1990s Hondas, the manuals say engine load, engine RPM, vehicle speed
and coolant temperature are fed into the ECU and then determine "basic ignition
timing." For 1995-1997 Civics, the manuals say ignition timing depends on engine
speed, manifold pressure, and coolant temperature. See for example, "Ignition
Timing" at http://www.honda.co.uk/owner/CivicManual/pdf/11-20.pdf .

Now these aren't VTEC engines, so maybe VTEC takes into account AIT in adjusting
timing.

> But, it gives a very much greater risk of
> catastrophic knock, which can effectively destroy the engine! Normally
> there is a certain amount of safety reserve built in and so generally
> you would get away with it, but things like this give me the *******,
> they really do.

I have the same feeling here, though it's based only on an impression and
textbook engineering and not much actual experience fooling with actual engine
controls.

 

"Caroline" <caroline10027remove@earthlink.net> wrote in message news:<1hWIc.7893$kK.4737@newsread3.news.atl.earthl ink.net>...
>
> Your theory sounds good enough, re wanting to change the timing at cooler engine
> temperatures, but from the manuals the actual engine control design does not
> appear to work quite this way.
>
> For circa 1990s Hondas, the manuals say engine load, engine RPM, vehicle speed
> and coolant temperature are fed into the ECU and then determine "basic ignition
> timing." For 1995-1997 Civics, the manuals say ignition timing depends on engine
> speed, manifold pressure, and coolant temperature. See for example, "Ignition
> Timing" at http://www.honda.co.uk/owner/CivicManual/pdf/11-20.pdf .
>
> Now these aren't VTEC engines, so maybe VTEC takes into account AIT in adjusting
> timing.
>
Agreed, it almost certainly depends on the engine. I actually set up
engine management systems for a living, and all the ones I work on
take AIT as an input to ignition timing. But these are on very new
vehicles and certainly some older vehicles with less sophisticated
management systems may well not take AIT into account.

Of course, the manual doesn't always give the full details of how the
system works either. The complete description for the management
systems I work with runs to 3500 pages - which is obviously highly
condensed for the vehicle workshop manual!

Tony

 

"Tony Cains" <nospam@tjcains.freeserve.co.uk> wrote
C wrote
> > Now these aren't VTEC engines, so maybe VTEC takes into account AIT in
adjusting
> > timing.
> >
> Agreed, it almost certainly depends on the engine. I actually set up
> engine management systems for a living, and all the ones I work on
> take AIT as an input to ignition timing. But these are on very new
> vehicles and certainly some older vehicles with less sophisticated
> management systems may well not take AIT into account.
>
> Of course, the manual doesn't always give the full details of how the
> system works either.

You better believe I would have bet beaucoup dollars on this before reading your
post. :-)

> The complete description for the management
> systems I work with runs to 3500 pages - which is obviously highly
> condensed for the vehicle workshop manual!

I would have guessed more than 3500 pages... ;-)

I've also been figuring the last few months (since I started studying the
details of auto emissions controls) that most of the information about each
model's design is most certainly proprietary.

(I did some control systems design work in grad school, with a touch of bona
fide consulting but as importantly, with occasional chatter with some Ford
emissions control system design-specialized engineers. They're the ones who gave
me some exposure to the practical side of emissions control design.)