Air filter and mpg.

David wrote:

> "Whoever" > wrote in message
> ocaldomain...
>
>>
>>On Mon, 12 Sep 2005, Daniel J. Stern wrote:
>>
>>
>>>On Mon, 12 Sep 2005, Whoever wrote:
>>>
>>>
>>>>>>>I just heard on a local car show that a dirty air filter only affects
>>>>>>>performance. It does not lower miles per gallon.
>>>
>>>>>>Doesn't lower performance usually equal lower MPRG?
>>>
>>>>>Only in the real world, not in the make-believe world of idiot car-talk
>>>>>radio show hosts who care more about laughing at their own dumb jokes
>>>>>than they do about providing good information.
>>>
>>>>Are you sure about this?
>>>
>>>Naw, ya caught me, I'm just makin' **** up as I go along. Yes, I'm sure
>>>of
>>>it. It's basic and very easy to understand.
>>>
>>>
>>>>Performance is usually measured as the maximum output from the engine. A
>>>>dirty filter will clearly reduce max output.
>>>>But MPG?
>>>
>>>Yes, MPG. Reduced airflow through the filter --> reduced airflow through
>>>the engine --> reduced power --> you push your foot down further to
>>>accelerate --> TPS tells ECM "More coal on the fire!" --> lower MPG.
>>
>>And I call BS. If the car has a MAF sensor, the amount of fuel that is
>>injected is a function of the mass of air that is inducted into the
>>engine. Result: engine runs at same A/F ratio, economy is unchanged.
>
>
> well if this stupid statement was correct, then a vehicles miles per gallon
> consumption should be the same regardless of load and speed!


No, not true. I agree with you that the statement isn't correct, but not
for this reason. His argument is that the throttle itself is nothing but
a restriction to air flow, so if you add restriction to the air FILTER
and compensate by opening the throttle further, then the MAF and O2
sensors will correct everything back to normal and mileage should be the
same as if there were no air filter restriction and more at the
throttle. If the A/F ratio was strictly computed from sensor readings,
he would definitely be correct. But A/F ratios are started from a fixed
baseline depending on RPM and throttle position, and then biased away
from the pre-set table by O2 and MAF sensor readings, thus there is
still some effect from a dirty air filter, because the bias offset has
to be larger. Its much the same with a carbureted car- the carburetor
*ideally* only cares about the speed of air flowing thru the venturi,
not the absolute pressure above the throttle plates because the float
bowl is also exposed to the same pressure. But we all know it doesn't
*quite* work that way.

On Tue, 13 Sep 2005, David wrote:

>
> "Whoever" > wrote in message
> ocaldomain...
>>
>>
>> On Mon, 12 Sep 2005, Daniel J. Stern wrote:
>>
>>> On Mon, 12 Sep 2005, Whoever wrote:
>>>
>>>>>>> I just heard on a local car show that a dirty air filter only affects
>>>>>>> performance. It does not lower miles per gallon.
>>>
>>>>>> Doesn't lower performance usually equal lower MPRG?
>>>
>>>>> Only in the real world, not in the make-believe world of idiot car-talk
>>>>> radio show hosts who care more about laughing at their own dumb jokes
>>>>> than they do about providing good information.
>>>
>>>> Are you sure about this?
>>>
>>> Naw, ya caught me, I'm just makin' **** up as I go along. Yes, I'm sure
>>> of
>>> it. It's basic and very easy to understand.
>>>
>>>> Performance is usually measured as the maximum output from the engine. A
>>>> dirty filter will clearly reduce max output.
>>>> But MPG?
>>>
>>> Yes, MPG. Reduced airflow through the filter --> reduced airflow through
>>> the engine --> reduced power --> you push your foot down further to
>>> accelerate --> TPS tells ECM "More coal on the fire!" --> lower MPG.
>>
>> And I call BS. If the car has a MAF sensor, the amount of fuel that is
>> injected is a function of the mass of air that is inducted into the
>> engine. Result: engine runs at same A/F ratio, economy is unchanged.
>
> well if this stupid statement was correct, then a vehicles miles per gallon
> consumption should be the same regardless of load and speed!

No, I neither said nor implied that. Engine (and car) efficiencies depend
on how they are operated. Load and speed clearly have an impact.

> specifically 23 MPG regardless of driving type, WOT or otherwise. Or are you
> saying the MAF has ESP and can tell the injectors to inject the exact amount
> of increased fuel before the throttle plate is opened to introduced the
> increased airflow? I guess we should really not even have a throttle peddle
> in the car as the MAF seems to do everything for us.

The MAF sensor measures air flow. The provide an inaccurate measure of
air flow. Your statement is nonsenical -- according to you a TPS can measure
throttle opening before it is opened!

There are plenty of reasons to have a TPS, irrespective of measuring air
flow into the engine.

>
>

On Tue, 13 Sep 2005, aarcuda69062 wrote:

> In article
> domain>,
> Whoever > wrote:
>
>> And I call BS. If the car has a MAF sensor, the amount of fuel that is
>> injected is a function of the mass of air that is inducted into the
>> engine. Result: engine runs at same A/F ratio, economy is unchanged.
>>
>> You seem to be assuming that the amount of fuel injected is a direct
>> function of throttle position. I don't think it is: I think it is a
>> function of the air mass flow as measured by the MAF sensor.
>
> Are you suggesting that the TPS has no authority over fuel
> delivery?
>
>> Think about what you are suggesting: tell me, do they adjust cars to run
>> in Denver these days? I don't think so with modern cars.
>
> Of course "they" adjust cars to run in Denver these days, it's
> just done in the engineering department by the OEM instead of a
> service shop. Just because it's handled by the PCM doesn't mean
> it isn't being done.

So, what you are saying is that the PCM can handle reduced pressure due to
reduced atmosperic pressure, but not reduced pressure due to a dirty air
filter?

What the heck do you think a closed loop system with O2 sensors, is
designed to do? It is designed to keep air/fuel ratios at the optimum
point -- and it adjusts for external factors such as atmospheric pressure
and dirty air filters

>
>
> There was an interesting number of posts a week or so ago by a
> Ford dealership tech on i-ATN regarding Fram air filters causing
> all manner of driveability problems because the element size is
> much smaller than what the system was designed for.
> (hmmm... wonder why?)

We are talking economy, not performance.

On Mon, 12 Sep 2005, Whoever wrote:

> > Reduced airflow through the filter --> reduced airflow through the
> > engine --> reduced power --> you push your foot down further to
> > accelerate --> TPS tells ECM "More coal on the fire!" --> lower MPG.
>
> And I call BS. If the car has a MAF sensor, the amount of fuel that is
> injected is a function of the mass of air that is inducted into the
> engine.

....and what the O2S says. And what the TPS says.

> You seem to be assuming that the amount of fuel injected is a direct
> function of throttle position.

Nope, I'm making no such assumption. You, on the other hand, are positing
that injector pulsewidth is a direct and sole function of MAF readings.

> Think about what you are suggesting: tell me, do they adjust cars to run
> in Denver these days?

Think about what *you* are suggesting: Tell me, is the MAF the only sensor
on the engine?

> But what do I know?

Good question.

On Tue, 13 Sep 2005, Whoever wrote:

> There are plenty of reasons to have a TPS, irrespective of measuring air
> flow into the engine.

Yes, especially since measuring airflow into the engine is not one of the
reasons to have a TPS.

On Tue, 13 Sep 2005, Steve wrote:

> David wrote:
>
>> "Whoever" > wrote in message
>> ocaldomain...
>>
>> >
>> > On Mon, 12 Sep 2005, Daniel J. Stern wrote:
>> >
>> >
>> > > On Mon, 12 Sep 2005, Whoever wrote:
>> > >
>> > >
>> > > > > > > I just heard on a local car show that a dirty air filter
>> > > > > > > only affects
>> > > > > > > performance. It does not lower miles per gallon.
>> > >
>> > > > > > Doesn't lower performance usually equal lower MPRG?
>> > >
>> > > > > Only in the real world, not in the make-believe world of idiot
>> > > > > car-talk
>> > > > > radio show hosts who care more about laughing at their own dumb
>> > > > > jokes
>> > > > > than they do about providing good information.
>> > >
>> > > > Are you sure about this?
>> > >
>> > > Naw, ya caught me, I'm just makin' **** up as I go along. Yes, I'm
>> > > sure of
>> > > it. It's basic and very easy to understand.
>> > >
>> > >
>> > > > Performance is usually measured as the maximum output from the
>> > > > engine. A
>> > > > dirty filter will clearly reduce max output.
>> > > > But MPG?
>> > >
>> > > Yes, MPG. Reduced airflow through the filter --> reduced airflow
>> > > through
>> > > the engine --> reduced power --> you push your foot down further to
>> > > accelerate --> TPS tells ECM "More coal on the fire!" --> lower MPG.
>> >
>> > And I call BS. If the car has a MAF sensor, the amount of fuel that is
>> > injected is a function of the mass of air that is inducted into the
>> > engine. Result: engine runs at same A/F ratio, economy is unchanged.
>>
>>
>> well if this stupid statement was correct, then a vehicles miles per
>> gallon consumption should be the same regardless of load and speed!
>
>
> No, not true. I agree with you that the statement isn't correct, but not
> for this reason. His argument is that the throttle itself is nothing but a
> restriction to air flow, so if you add restriction to the air FILTER and
> compensate by opening the throttle further, then the MAF and O2 sensors
> will correct everything back to normal and mileage should be the same as
> if there were no air filter restriction and more at the throttle. If the
> A/F ratio was strictly computed from sensor readings, he would definitely
> be correct. But A/F ratios are started from a fixed baseline depending on
> RPM and throttle position, and then biased away from the pre-set table by
> O2 and MAF sensor readings, thus there is still some effect from a dirty
> air filter, because the bias offset has to be larger. Its much the same
> with a carbureted car- the carburetor *ideally* only cares about the speed
> of air flowing thru the venturi, not the absolute pressure above the
> throttle plates because the float bowl is also exposed to the same
> pressure.

No. I ti sabsolutley different to a carburetted car -- a carburetter is an
open-loop device. There is no compensation for changes in pressure, and
other factors.

You describe the MAF and O2 sensors compensating for the differences. Just
because the bias offset may be bigger, why would that make the engine any
less efficient? It's just an adjustment to the amount of fuel injected to
keep the A/F ratio correct.

Essentially, what you and other are arguing is that, with a dirty filter,
the A/F ratio will be wrong, despite a closed-loop system and despite air
flow being measured by a MAF sensor.

On Tue, 13 Sep 2005, Daniel J. Stern wrote:

> On Mon, 12 Sep 2005, Whoever wrote:
>
>>> Reduced airflow through the filter --> reduced airflow through the
>>> engine --> reduced power --> you push your foot down further to
>>> accelerate --> TPS tells ECM "More coal on the fire!" --> lower MPG.
>>
>> And I call BS. If the car has a MAF sensor, the amount of fuel that is
>> injected is a function of the mass of air that is inducted into the
>> engine.
>
> ...and what the O2S says. And what the TPS says.
>
>> You seem to be assuming that the amount of fuel injected is a direct
>> function of throttle position.
>
> Nope, I'm making no such assumption. You, on the other hand, are positing
> that injector pulsewidth is a direct and sole function of MAF readings.

No. I did not say that.

>
>> Think about what you are suggesting: tell me, do they adjust cars to run
>> in Denver these days?
>
> Think about what *you* are suggesting: Tell me, is the MAF the only sensor
> on the engine?

Ah, that's right, don't respond to my question.

Clearly, the MAF sensor is not the only sensor. Did I say it was? Did I
say the fuel injected is solely a function of the MAF sensor reading? If
you think so, then I suggest you take some lessons in comprehension.

Anyway, please explain why the O2 sensor readings are not used to adjust
the A/F ratio to take account of variations such as dirty filters?

There is one other factor, which is that the difference in pressure drop
between a brand new filter and one that has been used for a 1000 miles is
probably far greater than the difference than that filter after 1000 miles
and after it has passed its proper life. But I will be frank and tell you
that I am guessing here.

On Tue, 13 Sep 2005, Whoever wrote:

> We're talking economy, not performance.

The two are inexorably linked, despite your handwaving. Let's put it in
real-world terms: Mr. Green and Mr. Black live on the same block in
Englewood, a suburb of Denver. They both work at Beau-Jo's in Idaho
Springs, 44 miles away, and they drive identical cars. Mr. Green changes
his air filter on schedule, while Mr. Black tends to let it slide until
the car is running noticeably poorly.

Both Mr. Green and Mr. Black take the same route to and from work every
day. They take Quincy Ave. East to I-25 Northbound (an uphill onramp),
I-25 North (a gentle uphill climb) to 6 West (an uphill flyover) to 70
West, at which point the remaining 19 miles of the trip are a fairly steep
climb.

Because Mr. Black neglects his air filter, airflow through his engine --
and therefore power -- at any given throttle opening is less, so he must
push the accelerator further down to accelerate and climb the hills. On
the onramps that require rapid merging, and on the uphill climbs, he
frequently pushes the accelerator down both to the point where the ECM
looks at the TPS and says "Oh! Rapid acceleration! OK, let's get that
acceleration enrichment subroutine online. More pulse width!", and to the
point where the ECM looks at the TPS and says "Oh! We're at WFO!" and goes
into open-loop operation.

Because Mr. Green maintains his air filter, airflow through his engine --
and therefore power -- is not reduced, so he needn't push the accelerator
down as far as Mr. Black. Therefore, less acceleration enrichment and
less open-loop operation.

Now, the $64,000 question:

WHO BURNS MORE FUEL?

Whoever wrote:

> No. I ti sabsolutley different to a carburetted car -- a carburetter is
> an open-loop device. There is no compensation for changes in pressure,
> and other factors.

Really? Are you SURE you want to stick with that statement? For all
carbs? For all factors? ;-) I claim that carbs (at least the 4 I own)
are actually pretty WELL compensated for the case of a dirty air filter,
because the float bowl sees the same lowered pressure (caused by the
dirty filter) as does the venturi, and therefore its compensated.... but
not necessarily PERFECTLY, which is the same as for software operating
highly skewed away from the basic lookup tables.
>
> You describe the MAF and O2 sensors compensating for the differences.
> Just because the bias offset may be bigger, why would that make the
> engine any less efficient? It's just an adjustment to the amount of fuel
> injected to keep the A/F ratio correct.

You're right, and it stays CLOSE. But, depending on the programming of
the PCM, there will be a skewing of the A/F ratio.


>
> Essentially, what you and other are arguing is that, with a dirty
> filter, the A/F ratio will be wrong, despite a closed-loop system and
> despite air flow being measured by a MAF sensor.
>

Depending on the programming of the PCM, that is true to varying degrees.

On Tue, 13 Sep 2005, Whoever wrote:

> Anyway, please explain why the O2 sensor readings are not used to adjust
> the A/F ratio to take account of variations such as dirty filters?

Because the driver's foot has crammed the accelerator to the floor to
accelerate because his air filter is plugged up, so the engine's in open
loop. Next dumb question?

> But I will be frank and tell you that I am guessing here.

And I will be Daniel and tell you that you're full of it.