Air filter and mpg.

The grandparent post described an open-loop situation and was equating this to fuel injection using a MAF sensor.

So, what you are saying is that the mathematics done by the PCM are somehow limited?

Remember, we are talking about putting LESS fuel into the engine.

...has nothing to do with your incorrect statements, which you are now refusing ownership of. Interesting.

Oh, gee, yeah, gosh, what a silly statement for me to make. Glad you caught me on that one. Obviously, the ECM has an unlimited ability to compensate for any variable you care to name. No limits at all. *eyeroll*

What you are doing, Mr. Whoever, is yacking-off: typing to hear your keyboard rattle.

And you accuse me of using hand-waving arguments?

Once again, you quote me out of context and use wild exaggeration to try to make a point. My point was that the result of a dirty air filter is that to maintain the correct A/F mixture, the amount of fuel to be injected should be REDUCED.

Yes, I was a little careless in my writing, clearly: there are limits to the PCM's mathematics. But to think that the small differences due to a dirty air filter could not be with the range of calculations is frankly, ridiculous.

And to put it as simply as I can, the resulting situation is that the throttle position sensor is shouting "MORE FUEL! MORE FUEL!" and the MAF sensor is screaming "LESS FUEL! LESS FUEL!" What does the PCM do in the case of conflicting sensors? Depends on the programming. Since leaning out an engine is potentially destructive, most PCMs will err on the side of biasing the actual mixture closer to the default value, resulting in a richer-than-optimum mixture and lower efficiency (but a protected engine). At SOME point, its also going to result in an error code, because the PCM can't tell if its looking at a restricted intake or a sensor fault.

Its more a limit to what software can safely do in the case of conflicting or abnormal combinations of sensor inputs.

Yes, I do.

I quote only what you write. If you dislike what I quote, you should've written something different.

Wild exaggeration? What wild exaggeration would that be?

Yes, it should. Now, consider: When the ECM sees conflicting demands (for less fuel from the MAF, for more fuel from the TPS), what happens?

Yes, you were. Also in your thinking.

But what about the O2 sensor? Dirty filters are not a transient effect so the PCM should adjust the mixture bias based on the O2 sensor reading.

Just a thought: no-one has commented on my suggestion that there are much greater differences in pressure drop across the filter from when it is brand new to the first thousand miles than between end of service life and some time after that. Clearly, the PCM has to and does accommodate this.

Y'mean the one that's ignored during open-loop acceleration? Or some other O2 sensor?

That's because it was, as you yourself admitted, nothing more than an ignorant guess. You'll have to do better than ignorant guesses if you want people to comment on what you say.

YOU MUST NOT DO THAT

...otherwise somebody will bite your head off.

Write 100 lines "I must not be careless in writing"...

DAS

For direct contact replace nospam with schmetterling

Yes, I mean the one that affects LONG TERM TRIM. And hence affects the amount of fuel injected during open loop conditions.

All right. Let me assert that it is true. What's your response?

Sorry to jump into this, but it seems like you are missing one thing in your assertion that MPG doesn't suffer.

In the previous "one clean-filtered car vs. one dirty-filtered car" example, you are not accounting for both cars doing the SAME WORK. In this case, it must be assumed (because Daniel doesn't have all day to write a voluminous and legally exacting example) that both cars are keeping neck and neck throughout the trip. Whenever the dirty car struggles and requires additional throttle angle over that of the clean car (here's a tip: any non-slowing event), dirty boy's fuel delivery volume is GREATER than clean boy's.

The dirty car has an efficiency problem which, strictly from an A/F ratio standpoint, can be corrected with an ECM and sensors. WHEN corrected, more fuel is required to achieve an identical power output vs an identical setup equipped with a clean air filter.

Toyota MDT in MO

Nope, that's not what I'm saying. Did you see the part where I mentioned that (for instance) Ford MAF sensors up-date BARO readings at wide open throttle. If as you claim you were involved in the design of such systems, you'd know that wide open throttle represents -increased- pressure, not reduced pressure as your reply states.

To a point, problem is, they do not have infinite ability to compensate, and when they're lied to, problems occur.

Really? You read the post?

And if he's using a Macintosh...

Bill Putney (To reply by e-mail, replace the last letter of the alphabet in my address with the letter 'x')

Bzzt! When in open-loop mode, the O2S is ignored, therefore it has NO effect on the amount of fuel injected during open-loop conditions. You were obviously telling a fib when you claimed to have once designed EFI systems and MAF sensors.

"Is not."

Naw, that's when Macintologists start preaching the Gospel According to Jobs.

-DS (uses Macs...they're my computers, not my religion. They're still just better, though! ;-) )

Y'know, Whoever is really not doing himself any favours by delaying his response to the post below, for his stalling is giving me time to think of other means by which clogged air filters reduce fuel economy. For example, most vehicles sold in North America have automatic transmissions. Dirty air filter --> less airflow through engine --> less power at any throttle opening --> driver must push accelerator down farther to attain a given acceleration --> automatic trans kicks down out of top gear and torque converter unlocks more often --> reduced fuel economy.

Are we havin' fun yet?

And a modern transmission, adapting itself to the driving style it thinks it's seeing, starts getting even quicker to downshift...