Air filter and fuel economy

[jimbo231]

This might sound like a stupid question but i've always heard a dirty air filter will cause poor fuel economy. I was wondering why that is? Won't the maf sensor make the car to use less fuel is it's getting less air from a clogged filter?

 

[alohamonte]

will cause the engine to run rich - too much gas not enough air - which will caused the unburnt gas to be wasted as it goes out the tailpipe

 

[1998Exp]

You may not be able to get full power if the obstruction is heavy, but the effect of a dirty filter on a fuel-injected enginer will be minimal in normal driving conditions.

The filter manufacturers possibly want you to believe that all manner of bad things happen if you don't replace your air filter every x number of miles, but the fact is that the MAF measures the air flow and adjust the fuel amount accordingly.

will cause the engine to run rich - too much gas not enough air - which will caused the unburnt gas to be wasted as it goes out the tailpipe

 

[2TimingTom]

It won't run richer- the MAF and O2 sensors will adjust fuel based on how much air is coming in.

The reason is that since the engine is essentially nothing more than a big air pump, any restriction in the pump's path (either intake or exhaust) causes the pump to work harder to get the same result. Sucking air through a filter that is dirty requires more effort than a clean filter.

 

[alohamonte]

the engine is not "working harder" its not getting enough air for efficent combustion. so it's actually working less.

 

[Slowy]

breathe through 1" pvc, then breathe through a coffee stirrer
which one are you working harder to breathe through?

 

[2TimingTom]

the engine is not "working harder" its not getting enough air for efficent combustion. so it's actually working less.

But yet you're demanding the same performance out of the engine.

And that straw example above is perfect. If you could measure how many calories you are burning while breathing normally vs breathing through a coffee stirrer- which one do you think you would be burning more calories doing?

 

[apuszczalowski]

Basically, in the simplest wording.....

The engine has to burn more fuel with a dirty air filter to get the same results as it would with a cleaner (more open) air filter.

The straw example explains it best. Take a deep breath then blow through a normal straw. Now, take a deep breath and blow through a coffee stirrer, more work to do the exact same thing