You only got increased air flow at WOT. Must of the time the air flow
was limited by the throttle opening, not the air filter. I doubt if
the difference in overall restricition was more than a few tenths of a
psi even at wide opoen throtttle.
Assuming the new filter really did flow better than the stock, the
difference in pressure drop through the intake is going to be on the
order of hundredth of psi except at wide open throttle. It is true
that with a lower pressure drop in the intake system before the
throttle plate, you would have increased air flow for a particualr
throttle opening. However, increased air flow also implies more power.
So to maintian the same speed as before you installed the less
restrictive intake, you would just open the throttle a tiny amount
less, resulting in the same overall flow through the system, for a
particualr speed. I am confident you would not be able to tell the
difference in throttle openning to acheive the same power level just
becasue you changed the air intake. As far as the engine and the fuel
injection system is concerned, until you are wide open throttle, the
air filter is largely irrelevant as long as it is in reasonable
condition. Feedback fuel injection systems are designed to compensate
for changes far more significant that minor changes in the intake
tract pressure drop. Just going from Denver to LA would present a much
greater change in the pressure seen at the face of the throttle plate
than a simple air filter change. In closed loop mode, the PCM adjusts
the amount of fuel injected to achieve a certain air/fuel ratio.
Unless you change the response of the system to the O2 sensor
readings, the desired A/F ratio is not going to change. During closed
loop mode the PCM "learns" parameters it uses to correct other inputs
when running in open loop mode, so that as sensors drift over time,
the system can compensate. Changing the air filter to a less
restricitive design might change the reading of the throttle position
sensor for a given power level, but this would be compensated for by
the PCM after a few minutes of closed loop operation. At any rate, the
TPS is not used directly to determine the amount of fuel injected. Its
function is to indicate gross changes in the throttle positions. This
allows the PCM to anticipate changing conditions. It functions more
like an accelerator pump or dashpot than a direct fuel control.
The only time the potential increase in air flow trough the
replacement air filter should have made a difference was at wide open
throttle. Otherwise it was doing nothing except slightly altering
where the overall air flow into the engine was limited.
The fact that you reset the PCM is significant. To bad you no longer
have the car. It would be interesting to reinstall the OEM air filter
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