Air filter and mpg.

I just heard on a local car show that a dirty air filter only affects
performance. It does not lower miles per gallon.

On Sat, 10 Sep 2005, tomkanpa wrote:

> I just heard on a local car show that a dirty air filter only affects
> performance. It does not lower miles per gallon.

You can hear all kinds of funny jokes and fairy tales on car-related shows
on the radio...both National and local.

On 10 Sep 2005 11:08:10 -0700, "tomkanpa" > 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?

-- Christian

On Mon, 12 Sep 2005, Christian M. Mericle 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.

On Mon, 12 Sep 2005, Daniel J. Stern wrote:

> On Mon, 12 Sep 2005, Christian M. Mericle 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? Performance is usually measured as the maximum
output from the engine. A dirty filter will clearly reduce max output.

But MPG? On a car equipped with MAF and oxygen sensors? The only
difference with a dirty filter would be a small power loss due to the
extra energy required to pull the air through the filter -- but would this
be measurable?


>

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.

> On a car equipped with MAF and oxygen sensors?

Even on a car equipped with MAF and O2S.

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.

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.

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.

But what do I know? I only used to work on the design of MAF sensors, fuel
injection design systems, ignition timing controllers, knock detection.

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.

> But what do I know? I only used to work on the design of MAF sensors, fuel
> injection design systems, ignition timing controllers, knock detection.

Then you'd know that Ford vehicles (for example) outdate BARO via
the MAF reading at wide open throttle and that BARO is
extrapolated based of stored values in the PCM which equate to
what the volumetric efficiency should be at WOT, when things
don't match because of a restricted air filter, you get a skewed
BARO reading and incorrect fuel control.

You'd also know the many GM vehicles use both a MAF and a MAP
sensor and that the MAP sensor updates BARO at wide open throttle
and again, based upon calculations stored, will result in a
skewed BARO reading due to the pressure drop across the
restricted air filter.

But what do I know? I -still- fix IM-240 CO and CO/HC failures
on MAF equipped vehicles that are caused by 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?)

Of course since this is a Chrysler newsgroup and since (so far)
most Chrysler vehicles use MAP sensors only and that the MAP
sensor again is used at wide open throttle to up-date the BARO
reading, a restricted air filter will cause incorrect fuel
delivery.

"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! So then MPG in
the city compared to Highway MPG is a false reading as it should be
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.


>
> 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.
>
> 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.
>
> But what do I know? I only used to work on the design of MAF sensors, fuel
> injection design systems, ignition timing controllers, knock detection.
>

Whoever wrote:

>
>
> 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.
>

Not necessarily. Most ECMs try to run near their factory default
cailibration with the throttle position sensor as the primary input, and
use the O2 sensors and MAF or MAP sensors to apply correction factors.
Often, they tend to be a little less efficient as bigger and bigger
correction factors are needed. The effect may be small, but not absent.