is it possible to get too much air?

[Guest ttoude]

Is it possible to get too much air?

 

For context I'm looking for a flooding problem in the usual places but this kinda crossed my mind when i looked at the aftermarket filter and my ultrashort mount.

 

280 with 81/83 turbo swap (carbon fouled plugs)

[johnc]

Its called "lean" or "vacuum leak".

[Guest ttoude]

By too much air i mean all is sealed well, this question is more of directed toward the effect of aftermarket parts on engine performance ie fuel signal.

 

But i understand your defacto vac leak response, however those bases are covered.

[Daeron]

The short answer is no. If all is sealed well then that means no air is being pulled that is not being metered.

 

Air is metered in one of three ways (at least thats all *I* am aware of) in an electronic FI system: AFM, MAF, or MAP. There are technical terms (MAP I think is speed-density, and MAF is something else) but those are the three devices used.

 

The AFM (for Air Flow Meter) is a flappy box, obstructing a channel. The engine pulls air though that channel, lifting the flappy box, which is specifically counterweighted and attached to a potentiometer. A potentiometer is like a volume knob. The size of the passageway and the counterweight of the flappy box are calculated so that the signal corresponds to a certain volume of air flow, and the computer works with that (and sometimes temperature sensors) to determine fuel need.

 

The MAF (for Mass Air Flow) sensor is a pair of tiny wires that get heated up by electrical current passing through them. These wires are placed strategically into a pod on the side of an aluminum tube. The tube is the size of the air intake tubing and TB for the vehicle, and the air moving past the wires cools them down which changes the current draw. The computer senses this draw, and uses the data to infer the mass of air ingested by the engine. Since this is a more precise measurement of how much air has entered than volumetric metering, MAF is more accurate than AFM.

 

The most modern systems use MAP sensors, (for Manifold Absolute Pressure) and take the pressure readings, the engine RPM, the throttle position (determined by a potentiometer; older AFM systems frequently have throttle positions sqitches which are NOT potentiometers at all, simply three position switches for idle, cruise and WOT) and usually other factors, and multiply them all out against each other, and determine the fuel and spark requirements accordingly.

 

 

SO, to return to your original question: without vacuum or other air leaks, it is impossible to have "too much" air because the air ingested by your engine is used by the computer (or the carburetor for that matter) is used as a baseline to determine everything else.

 

What you CAN have is unmetered air entering your intake tract.

 

The difference between that, and "too much air" is semantic, but it is very profound.

[Tony D]

Actually Daeron, MAP (Speed-Density) systems are relegated to specific manufacturers that started with them originally.

 

MAF is far superior in sensing actual air mass going into the engine, and far more common these days.

 

With MAP you have to use lookup tables for pressure versus temperature and cross to engine speed and throttle position.

 

With MAF, 15 pounds per hour is always the same point on the table. Your fuel mix will only change based on scalars such as if you have rapidly moved the throttle, selected WOT, etc...

 

In the industrial world, Mass Flow is the standard for metrology on critical processes. Same in the automotive world. 15PPH is always 15pph. 225KPa can be any number of air molecules, depending on temperature.

 

And AFM was originally AFC (Air Flow Control), at least that's what VW called it when they went from the original MAP based systems used in their cars from 1968-1975, to the next generation of Flapper Controlled systems, which were eventually supplanted by AFM controlled systems. Each was a progressively better and more precise metering system than the previous generation.

 

As for 'too much air' question, it's never a question of too much air, it's ALWAYS an issue of too little fuel. The engine will pump what it will pump, the media you are adding is fuel. You match fuel flow to air flow---that's what the EFI system does. By definition you can't have too much air, only too little fuel. Fuel is the additive to the fixed volume of air the engien moves. Look at a diesel and you will understand...where's the throttle plate on a diesel?

[Daeron]

Actually Daeron, MAP (Speed-Density) systems are relegated to specific manufacturers that started with them originally.

 

As usual, I open my mouth, only to get my foot stuffed in it

 

I've always considered MAF based to be my preferred, and I have been considering posting to the effect of "I call MAF my favorite, but I can't give a good argument as to why. What are the manifest pros and cons of MAF vs MAP?" but.. I always come to the conclusion I'd be better off just reading up on it independently. Then I proceed to do nothing more than monitor such of the internet as I come across for that material. I know that ideally you run a blended MAF/MAP setup.. but since my "education" in this field has been limited to, well, this posting discussion here, I'm certainly in no position to step to the front of the class and start teaching.

 

Still, I try, and in doing I wind up saying something that needs correcting, despite my good intent. I need a foot-in-mouth emoticon...

[woldson]

If you don't go their, you will never expand your horizon.

 

Besides it gives TonyD a reason to post, so thankyou Daeron!!!

[Daeron]

If you don't go their, you will never expand your horizon.

 

Besides it gives TonyD a reason to post, so thankyou Daeron!!!

 

I know, and I'm cool with my role...

 

 

...theres just only so many ways one can say "Well, yah, THATS what I was trying to say, but he did a better job."

[Tony D]

Some places are not so happy to see a post-'o-mine...

 

I like the little yellow and black froggie. I thinks with colouration like that, he's a nasty little buggar... all poisionous and stuff! Totally lickable!