MAF operation ?

[tripleoption]

Howdy folks. At the risk of sounding like a fool, I'm going to ask a question. How does the MAF compensate for cooler air temperatures? Obviously, the air going into the engine is cooler in January than it is in July, and cooler air is more dense. The volume of the cylinders at ignition does not change, so either there is more air (in terms of mass) or more gas in the mixture, right?

Tell me what I'm forgetting. Thanks.

 

[Alec]

I don't know exactly how the MAS senses air flow, but it has a few wires that the air rushes past. The MAS senses air flow and volume, not density. The IAT, intake air temp sensor measures the temperature of the intake charge. Then the computer decides how dense the air is. The denser the air, the more fuel is added. This is one reason at a constant rpms, mileage will go down in winter because more fuel is being used.

 

[tripleoption]

Okay. So, does the ratio of air to fuel in the mixture change? It doesn't sound like it does. It sounds like the volume of air in the cylinder goes down and the volume of gas in the cylinder goes up, but the mass ratio between them stays the same.

Has anyone monkeyed with this ratio at all? (Maybe that's what the chips do?)

 

[Alec]

The computer is constant varying the ratio of air to fuel for max power and economy. Mine ranges from 13.0 to about 16.5. The stoichiometric value is 14.7:1.

 

[tripleoption]

Outstanding. Thank you, Alec. That's a word I have not heard in a long time...stoichiometric. I think I'll let my mind wander from this point. Once again, you 'da man. You get a gold star from me.

 

[MrShorty]

omega engineering supplies the mass flow meters we use in our laboratory. The link describes the basic operating principle of their mass flow meters. Essentially, the MAF measures the amount of heat removed from the sensor. When set up properly, this heat is directly related to the mass (or moles) and not density